Posner, M.I., Rueda, M.R. & Kanske, P. (2007). Probing the mechanisms of attention. In J.T. Cacioppo, J.G. Tassinary & G.G. Berntson (eds), Handbook of Psychophysiology, Third Edition. Cambridge U.K.: Cambridge University Press (pp 410-432). 1B Probingthe Mechanisms of Attention MICHAELI. POSNER, M, ROSARIO RUEDA,& PHILIPP KANSKE ABSTR/TCT time, Hebb (1949) called attention to the importance of networks of neural areas (cell assemblics and phase This chapter emphasizes the manlr methods currently sequences)in building conscious reprcsentation of stimbeing employed to study brain networks related to attcnulus input (see Posner & Rothbart, 2004 fbr a levie',v of tion. We seek to sct current studies into a historical backHebb's contribution). In the last fifty years there has been ground of efforts to understand how the brain selects steadyprogress in the development of methods that allow among stimuli and resolves competing responses. We us to probe the mechanismsof attcntion at a ph-ysiological examine attention as an organ system with netrvorks of level. It is the developmentof these mcthods and their use neural areas rclatcd to several major functions such as to probe attentional networks that seemsmost relevant to maintaining the alert state, orienting to sensory events the curent handbook. and resolving conflict bet$'eenresponses.We consider the In this chapter we first trace history of the developmcnt anatomy and circuitry of these networks and examine of mcthods that allow study ofattcntional separatelyfrom the rolc of genesand experiencein their normal developothercognitive functions. We cxamine the methods used to mcnt and of various pathologies.Finally we examine how link attention to underlying brain mechanisms including our currcnt knorvledgeof the psychophysiologyof attenstudies of lesionedpatients, recording ofelectrical activity tion illuminates traditional issucsin cognition about how noninvasivelyin humans orby use of implanted electrodes attenlronopcrates. and efforts to understand the genes related to attcntion. The field of attention is one of thc oldest in psycholThese include the use of microelectrodes in aler.tanimals og]. At the turn of the twentieth ccntury Titchener (1909) beginning in the 1970s and early studies of neuroimag"thc called attention hcart of the psychologicalenterprisc." ing using hcmodynamic methods starting in the 1980s. Attention is relatively easy to define subjectively as in the After our historical review, we examinc curcnt studies "Everyone classical definition of William Jameswho said: within cognitive psychology to get an idea of the luncknou,s u'hat attention is. It is thc taking possessionof the tions of net.t'"orksin vigilance, visual search,and cognitive mincl in clear and vivid form of one our of what seem sevcontrol tasks. We then examine thc anatomical net$'orks cral simultaneous obiects or trains of thought." (James, that underlic thesc functions using wher-reverpossible thc 1890,p. 403). However, this subjective definition does not combined methods that have developcd ovcr thc lasLhalf prof ide hints that might lead to an understandingof mechcentury to explore neural networks. We then consider evianisms of attention that can illuminate its physical basis deuceofhow genesand experienceshapethc dcvclopment in terrns ofundcrlying physiological processnor clarify its of attentional networks. At the end wc rctum to some of normal dcvclopment and pathologies.For thcse goals it is the major questions in cognition that concern attention useftll to think about attention as an organ system \\,ith and rcvicw their current state. its own anatomy and circuitry that develops in early life under the control of genesand experience.This will be the Iocus of our chapter. M O D E R NH I S T O R Y Thc modern history of attcntion as an organ can be started with the important stucliesof Maruzzi and Magoun 'l950s (19,+9)on thc reticular activating system.About the same D. O. Hebb (1949)arguedthat all stimuli had tu'o eflects. One of these, following the studies of Mamzzi and Magoun, involved the reticular activaling system and The au!ho^i would likc to ihankPnrf. Mary K. Rothbart for herpanic, worked to keep the cortex luned in the \\,aking state, ipatiou in this research and colleagues ar lhe Universitv of Oregon and the Sackler Inslilr.rle at Weill Medical Collcge of Cornell Universiiy. whereas the other uscd the great sensory pathu,ays and 410 411 P R O B I NTGH EM E C H A N I S MOSFA T T E N T I O N providcd information about the nature of the stimulating event. In the early 1950s,Colin Cherry (Chcrry 1953) initiated an cpic senes of experiments designcd Lo cxamine how sub.jcctsselected stimuli that were presented simulLaneously lo each ear. A major result was that rapid prese[tation of pairs of digits one to each ear, led people to recall of all digits presented to thc right ear first, followed by all presentedto the left. Broadbcnt(1958)summarizedthese and other results by suggesting that a peripheral shortterm memory syslcm buffers sensoryinput prior to a filter, u,hich selectsa channel of entry (in this casean ear) and sendsinformation to a limited capacity perceptual system. A second linc of attention research that emerged from studies conducted in the Second World War involvcd thc study of sustained attention during vigilance tasks (Mackworth & Mackq'orth, 1956). During continuous tasks subjectstendcd to miss more signals as the task continued. Changesin the EEG suggcstcdthat there was an increascin a sleep-likestate. 1950s One ofthe big developmentsof the 1960sinvoh'ed the ability to averageelectrical signals from the scalp to develop th(] cvent-rclated potential, as a series of electrical events timc locked to the stimulus. The technique was applied to the stu.lyof.rttention.In 1965Sutton (Suttonet al., 1965) reported that surprising or uncxpectedcognitive events,of the typc lhal might be closely inspectedproduccd a strong positive rvave in the scalp potential called the P 300. This component has and continues to play an important role in attention research(Donchin & Cohen, 1967;Rugg & Coles, 1995). At about the same time Gray Waltcr rcportcd that the brain prodrrcccla marked DC shift during the period follor.r'inga rvarning and prior to a target, this rvas called the contingent negativevariation andwasviewed as a sign that alerling was t.rking place (Walter et al., 1964).Reaction time improved markedly ovcr thc lirsl 500 milliseconds follorving thc u,arning and often, errors increased with rvarning intenal, producing a tradcoff between speedancl accu:acy.This linding suggestedthat $,aming effects did not improve the accmal of information but instead made it faster to attend to thc input and thus sped the response (Posner;1978). superior colliculus and parietal lobe. Their findings suggested the importance of both of these arcas to a shift of visual attention. It had bcen known for many )rcars that patients with lesions of the right parietal lobe could suJFer from a profound neglect of spaceopposite the lesion. The "attention findings of related cells" in the posterior parietal lobe of alcn monkcys suggcstedthat thcsc cells might bc responsible for the clinical syndrome. An impressiveresult from the microelectrode work, was that the time course of parietal cell activity seemed to follou'a visual stimulus by 80-100 milliseconds.Beginning in the 1970s,Hillyard (van Voorhis & Hillyard, 1978) and other investigatorsexplored the use of scalp electrode to examine time differences betrveenattended and unattended visual locations. They found that. the N 1 and P2 components of the visual cr,cnt related potential sho\\,ed changesduc to attcntion starting at about 100 milliseconds after input. Theselinding shou'edlikell' convergence of the latencl' of psychological processesas measured b-v ERPs in human subjectsand cellular proccssesmeasured in alert monkeys. This finding was a very important development for mental chronometry becauseit suggestedthat scalp recordings could accurately reflect the underlying temporal stmcture of brain activity. 1980s Posner(1980) studied the use of a cue in an othenvise empty visual field as a way of moving atteDtion to a targct. Electrodes near the eyes \\,ere used to insure thcrc were no eye movements and because only one response u'as required there was no \!ay to prepare the response differently depending upon thc cuc, making it clcar that whatever changes were induced by the cue \\,ere covert and not due to motor adjustment of the eyesor hand. It q'as found that co\,eft shifts could enhance the speed of responding to the target even in a nearly empty field. within half a second,one could shift attention to a visual event and, rvhen it indicated a likely target at another location, movc attcntion to cnhancc proccssing aL the new location. It was shorvn (Shulman, Rcmington, & Mcclean, 1979)that responsetimes to probesat intermediatelocations wcre enhancedat intermediate times as though altcntion actually moved through the space and that it $'as possiblc to preparc to movc thc cyes to one location while moving attcntion covcrtly in the opposite direction (Pos ner, 1980). Whether attention moves through the intermediate space and how free covert attention is from thc 1970s eyemovement s!stems are still disputed matters (LaBerge, Thc r.r'orkoi Hubel and Wiesel (1968) using microclcc- 1995;RizzolatticLal., 1987),suggcstingthc limitation of trodes to probc the structure of the visual system began purcly behavioral sLudies. At the time, it rvas also hard to understand hor.v a in the earlv 1960s.Horvevei before this method could be applied to attention it \\'as necessaryto adapt the micro- movement of attention could possibl,vbe executeclb-vneu electrode technique to alcrt animals. This was accom- rons. Subsequentlyjt urasshovn that the population vecpJishedin thc earl1 1970sby Evarrs(1968)and appliedby tor of a set of neurons in the motor system of a monMountcastle(1978)and Wurtz, Goldberg,and Robinson ke-vcould cann'out what rvould appear behavioralll, as (1980)to examinemechanismsof visual attention in lhe a mental rotation (Georgopoulosct at., 1989).OK,After 412 thart finding, a covert shift of attention did not seem too far-fc t checi. It had been rcported that patients u,ith lesions of the parietal lobe could make same-different judgments concerning objects that theywere unable to report conscioLlsly (Volpe, LeDoux, & Gazzaniga,1979).It rvaspossibleto fbllou,this rcsult in more analytic cognitive studies.What did a right parietal lesion do that made accessto material on the leli sidc dilEcult or impossible for consciousnessand )et still lefi the information available for otherjudgments? This puzzle qas partially ansu'ered by the systematic study ofpatients with diffcrcnt lesion locations in the parietal lobc, thc pulvinar and the colliculus. Theselesions all tendcd to shorv neglect of thc sidc of space opposite the lesion. But in a detailed cognitive analysisit was clear that they diffcrcd in shorving deficits in spccific mental operations involvcd in shifting attention (Posner, 1988). These sludicssuppofieda limited form ofbrain localization.The hlpothesis was lhat different brain areas executed indir,idual mental operations or computations such as disengaging from the current focus of attention (parictal lobe), moving or changing the index ofattcntion (colliculus), and engaging thc subsequenttarget (pulvinar). If this hypothcsis were correct it might explain why Lashley thought the u,hole brain was involved in mental tasks.Perhapsits not the whole brain, but a widely dispersednetwork of quitc localized ncural areas. POSN E R ,R U E D A&, K A N S K E during hemodynamic imaging (scc Dale et a1.,2000, for a revie$,).In somc areasof attention there has becn extensivevalidation of thesealgorithms (Heinze et al., I 99,1)and thev allou'precise data on thc scquenceof activations dur. ing the selectionof visual stimuli (seeHillyard, Di Russo, & Marlinez, 2004 for a review). The combination of spatial localization rvith hemodynamic imaging and tcmporal precisions tsom electrical rccording has provided an approach to the networks underlying attention. At the turn of the century the ovcrall sequenceof the human genome had been accomplished (Venter et al., 2001).Although humans have a common genome thcrc are differences among individuals, in many genes (polymorphisms). Thesediffcrcnccs make itpossible to examinc pafiicular genesrelated to individual diflercnces in beharior and in brain activity (Goldbcrg & Weinberger, 200,1; Mattay & GoJdberg,200'1). COGNITIVE STUD!E5 The cognitive approach to attention provides a varicty of models and conceptual framcworks for braiu stutlies. Per. haps the most generalissueis whetherto think ofattention as one thing or as a number of somewhat separatc issues. A classic distinction in the 6cld is to divide attention by considering separatelythc intensive and selectiveaspects (Kahneman, 1973). Attentional states varv. Thcy include slor,,'wave sleep, coma, rapid eye movement sleep, and degreesof wakefulnessthat mayvaryover the courseof the 1990s to Date day (dirurnal rhvthm), time on task or following rvarairgs. ln the late 1980s, thc Washington University School of Thesestatcscan be contrastedwith selectivcat-tcntionthat Mcdicine was developing a PET center led by Marc involvesthe mechanismsin committing resourcesto some Raichle. These studies helped establish neuroimaging as particular event. a mcans of cxploring brain activity during cognitivc funcIn this chapter rve follou' a division of attention into tious in general and the study of attcntion in particular. three distinct netu'orks: one of these involves a changc (Posner& Raichlc, 1994, 1998).In general,these stud- of state and is called alerting. Thc othcr two are closely ies have shown that most cognitive tasks, including those involved with the selection and arc called orienting and that are designcd to separate mechanisms of afiention, executi!'econtrol (Posner& Petersen,1990).Alerring deals have activatcd a small number of r.videlyscattered neu- with the intensive aspcct of attention related to how the ral areas. Some peoplc have argued that these areas arc organism achievesand maintains thc alcrt statc. Orient, specificfor domains of function like languagc,facc percep- ing deals with selectivemechanisms operating on sensory tion, or episodic memory (Kanwisher & Duncan, 2004).In input. The idea that new senso{, stimuli lcad to an orithe area of attention it has been more frequent to consider enting reflex goes back to the classic studies of Sokolov the mental operations or computations carried out by a (1963) on peripheral changes underlying thc oricnting particular arca (Corbetta & Shulman, 2002; Posncr,2004). rcflcx, but rnuch new has been learncd about the br.rin s]'sThese two idcas are not mutually exclusive.It is certainl_y tems involved. Thc cxecutive network deals $'i1h conJlict possible to talk about the set of areas that are involved among competing responsesand related to issucs such as in language and at the samc t-imemaintain that the areas the developmentof self-regulationnot only of thoughts but cal-ll out different computations $,ithin that domain. also of feelings and behavior (Rueda, Posner,& Rothbart, Thc findings from neuroimaging that cognitive tasks 200,1).Although in much of our behavior all of thcse netinvolvc a number of different anatomical areashas led to works arc involved simultaneously, the distinction allows an emphasis on tracing the time dynamics of these areas us to ref iew somewhat different literatures. during tasks inl'olving attention. Becauseshifts of attention can be so rapid it is difficult to follow thcm q,ith ALERTING hemodynamic imaging. To fill this role, algorithms have bcen developed (Scherg & Berg, 1993) to relate the scalp The state ofwakefulness and arousal is influenced bv interdistribution recorded fiom high density electrical or mag- nal and externalsignals (Hackley& Valle-Inclan,1998). netic sensors on or near thc skull to brain areas active Intrinsic or tonic alertnessclearly changcsover the coLtrse P R O 3 I NT GH EM E C H A N I S MOSFA T T E N T I O N lr' of the day from sleep to waking and uithin the \\aking statc from sluggish to highly alen. Originally these effects ',verethought to involve a single mechanism, the reticular activating system,but current researchconsidersthe interpla-vof a number of midbrain neural modulators such as norepinephrineand dopamineto bc invoh'ed.In all tasks involving long periods of proccssingthe role of changesof statc may bc imporlant. Thus vigilance or sustainedattention cffccts probably rest at least in part on changes in tonic alerting system. The presentation of an external stimulus can also increase alertness.The clearest case can be obsen'ed as a rcduction in rcaction times in tasks in rvhich a r.varning signal is presented prior to a target. This cffect is patly automatic as it can occurwith an auditory accessorye1,cnt, rvhich cloesnot predict a target. It is partly due to voluntan'arctionsbasedon the inforrnation about the time ofthc upcoming targct. Thcseeffectscanbe obsenedas a general DC shift in electrical activity of thc EEG called the contingent negati\,evariation (Walter et al., 1964).However,more spcci6c ncgativc shifts ma.,'alsobe seenin particular stnlctures depending upon the target or activity rcquired il the task (Rosler,Hcil, & Rodc4 1997). Alertnessreflectsthestate of theorganismforprocessing infbrmation and is an important condition in all tasks. Tt is also possiblctlistinguish effects of alertnesson sensory input from its elfecton moLorsystems(Sanders,1998). ORIENTING When examining a visual scenethcre is the generalfeeling that all information about it is available. Hoq,ever,careful cxpcrimcntal studies (Rensink, O'Regan& Clark, 1997; Rock & Clrttman, 1981)havc shown that this is not the case.Important semantic changescan occur in the sccnc ',vithout any repor'tofthe obsen er provided they take place arvay fiom the focus of attention and cues that are normaily effective in producing a shift of attention such as luminance changes or movemcnt arc suppressed.Thesc lindings, callcd changcblindness,underlie the importance of atlcntion shiftsfor normal conscjousperccptiol. The study of visual orienting has often involved the usc ofvisual scarch tasksin which a particular object is de6led as a target (Treisman & Gelade, 1980).Visual search has becn uscd to sludy limits to the amount of information containcdin:r scenethat is passedon to highcr processing (Broadbent,1958;Treisman& celade, 1980).A r.vidcly used metaphor for this capacity limit (Cavanagh,2004) \,ie\\'sattention oricnting as a spotlight that enablcsexamination of detailsrvith:n the spollightu'hilereducingrthat can be reportedoutsidethe spotlight. When the target dilfurs in a single element foom all the background rcacLion timcs generally are similar irrcspectivc of the numbcr of clements as though thcy pop ollt from the background. Hor.vcver,when the target and background havc attributes in common reaction times generally increase linearly with the number of background elementslconjunctiorlsearch.(Trcisman & Galade,1980).Thc 413 idea ofconjunction searchsuggestsa single focus of attention that is moved at all over thc visual display. Indccd when the array is large, evc movements are a major vchi, cle for moving the focus of attcnlion from one location to arother. Horvever',similar results can be obtaincd even t'hen the eyes are fixed and this underlies the idca that attentjon can be viewcd as a covert spotlight. Severalrccent studies suggestthe cxistence of multiplc spotlights(Yantis,1992;Kramer & Hahn, 1995).Arvhand Pashler(2000)were able to demonstratethatjust an extcn, sion in sizeof the spotlightis not sumcientto explainall of thc extart data. Ho$'ever,it scemsthat the size of thc selection region can vary extensivelyin corrcspondenceto what is demanded by the task (Klcin & McCor-rnick,1989).The minimal selectionregionwithina fixationcanbe describcd as a co\rert aclrit-ylimit (Intriligator & Cavanagh, 2001). Cavanagh(2004)arguesfor another limitation he calls coding singulariiy. Within the selectionregion it is not possible to fnrthcr scmtinize details, instcad a single label is passed on fbr the entire region (Nakayama, 1990).Of course coding singularity is thc basisfor the acuity limiL but the acuity limit determincs the minimum selection region. Visual orienting is an important model becausc of the closecoordination betrveenovert motor atctivit-yand intcrnal covert selection. Overt and coverl shifts of attention often go together. Shifts in gazc seem to be preccdcd by covcrt orienting of attention. This tight linkagc betu,een covert and overt oricnting is supportcd by neuroimaging data showing extensiveoverlap in the corresponding brain regions. The behavioral and imaging clata support the oculomotorreadinesshypothesis(Klcin, 1980;seealso "pre-motor theory" Rizzolatli ct al., 1987) stating that cndogenouscovert orienting is the preparation of an eye movement.Ho\.\'ever,the two predictions arising trom this hypothesis, faster eye mo\€ments to attended locations and facilitated detection of events at locations to which an cyc movement is being prepared, havc not been completelysuppofted(Klein,2004;Hunt & Kingsronc,2003). It is possible that endogenous covert and ovcrt {)rienting are isolable systems. Klein (2004) formulatcs three "Thcre conclusions: is a tight linkage bctr.vccnsaccade cxccution and covert visual orienting . . . ovefi and covert orienting are exogenouslyactivated by similar stimulus conditions (and) endogenous covert orienting of attention is not mediated by endogenouslygeneratedsaccaclic programming." AlLhoughhead or eyc movcments can achicvc overt orienting, most researchon overt orienting has concentratcd on one t1pe of eyemovement, namely saccades.If subiects are required to perform a saccadcto .r peripheral targct, the saccadicrcaction time is shortencd r.vhena Sxation or anoLhcrpcripheral signal is turncd off shortly abour 100 200 ms, belbre the targct appears (gap effect) (Schiller, Sandell,& Maunsell,1987).Klein and colleagues(Klein & Kingstone, 1993;Taylo4,Kingstone, & Klein, 1998) pro, posed a three-component-moclel explainingthis pattern: An offsct of any stimulus in the cnvironment can incrcase alertnessby functioning as a warning signal. As depicted 414 above, reaction times decreasewith incrcasing alertness. Also, becauseof the disappearanccof a signal the oculomotor svstem u'ill be exogcnously disengagedand there has to bc an endogenousdisengagementof the oculomotor system as in the natural environment objects offixation rarely disappears. A task that is widely used to study endogcnous control of overi orienting is thc anti-saccadetask in rvhich a saccadeaway from a target is 1<lbc performed. Hor,"ever, Klein (2004) points out that this procedure is "messy" as it includes more than onc endogenousorienting computation. The endogenous attcntional computation as well as the er-rdogenous execution of the saccadehas to be pertbrrned. Additionally, an exogenouslycontrolled saccade to the target has to be inhibited. The oculomotor capture paradigm (Theeuweset al., 1998)explicitlyenablesexploration of thc interaction between exogenousand endogcnous orienting. Results of this rcsearch and the evidence provided above suggesta competition of endogenousand exogenous signals for control of the oculomotor system (Klcin,2004). Another important charactcristic of the orienting netu'ork is an inhibitory function. Inhibition in generalin cognilive tasksis inferred from an increasein reaction time or an increasederror rate. In orienting tasks when a peripheral cue is prcsentcd more than 300 ms beforc a target, inhibition takes placc at the location of the cue and reaction time at that location increases.This effect callcd inhibition of return (IOR) (Posner& Cohen, 198.1)suggested that the initial exogenousshift of attention to the cued location has been tcrminated and a retum to that location is nou'inhibited. IOR can alsobe obsenedin tasksin which r-rot only one peripheral cue is presentcd as described abovc (single cue procedure) but also when a center cue is presented between thc presentation of the peripheral cue and thc targct (double-cue procedure). Fuentes and colleagues (Fuentes, Vivas, & Humphreys, 1999) demonstratc that when more complex stimuli are presentedat the cued location, and thus inhibited, they were less likely to elicit scmantic priming compared to primes presentcd at an uncued location. These authors also applicd Eriksons fJankerparadigm(Erikson& HofTrnan,1972,1973),r,hich consistsof the presentationof a centralstimulus(e.g.,an arro$,) accompanied by either congmous (anorvs poir-rting in thc same direction) or incongr-uous(arrows point' irg in the opposite direction) stimuli. When the llankers arc prcsented at the cued location, contrary to the usual results, congruous flankers produced longer RTs compared to incongr-uousflankers. Fucntes (2004) called this effect inhibitory tagging, a mechanism temporalJyinhibiting "the links between thc aclivalcd representations of inhibitcd stimuli and their appropriate response." Data from parietal anci schizophrenic patients show that IOR and inhibitory tagging, although both aflecting stimuli al already explored regions are scparate inhibitory mechanisms (Vivas,Humphreys, & Fuentes,2003;Fuenteset al., 2000). IOR fulfills an important function as it prcvents rcexamination of locations that have already been explored POSNER R,U E D A&, K A N S K E (Klein, 2000).As alertnessis incrcasedu'ith changing em'ironmental conditions, it seemsas if orienting and alerting bias the organism for lovelty and change. EXECUTIVEATTENTION An important vehicle lbr studying cxecutive attention is to inducc conflict betiveen rcsponse tendencies particularly where the person is to executethe subdominant responsc while suppressingthe dominant tendency(Botvinick et al., 2001).For examplc,in the Strooptask,a dominantbccause welllearncd rcsponse (reading a color,,vord) has to be oppressed in favor of a less dominant response (naming the color a word is printcd in). The flanker task r,''ould bc another exarnplein $'hich a target stimulus is surrounded eithcr by congruent or incongruc[t fl.rnkers for a conJlicting responsesituation. Executiveattention is also rcquired il qror commission, in working mcmory tasks (Barddeler', 1993)or in problem solving. Executive attcntion has been examined by dcvcloping neural netrvork models. A Lhcoreticalmodel dealing u,ith executive,controlling functions of attention has beerrpresented by Cohen, Aston-Jones, and Gilzcnrat (2004) b-v modifying an earlier model of the Stroop task (Cohen, Dunbar, & McClelland, 1990). The model is made up of units, lvhich are organized in two path\\,ays,a color nam ing pathway and a u'ord pathway. Each pathway con tains stimulus units projecting to associativeunits, which projcct to verbal response units. If thc conncctions arc stronger in the word pathway the modcl will be biased towards reading the word and not naming the color, similar to humanbehavior. To bc able to also exp)ainthe human capability of overiding this prepotent responsetendcncy to name thc color and not read the u'ord thc modcl was modi6cd. Task demand units r^.,erc includcd each of r,vhich matches to a certain task (read a word or name the color). As these task demand units are connectcd to thc associative units in the corresponding pathlvay; activation of a task demand unit \\'ill modulate the activit-vof these associative units and bias the system. It is norv possiblc for the model to not read a u'ord in favor of naming its color and thus to show execLltivecontrol. Similar models have been proposcd to account for other functions of the exccutivc attention network. Botvinick and colleagues(2004) demonstrated that adding a conflict monitoring unit to models of differcnt tasks could account for bchavioral and neuroscientific results, that occur with making an error. Another approach to executjve attention is to examine similarities between oricnting Lo informaLion in longtcrm mcmory and orienting to sensory information. A mechanismsimilar to inhibition of retum in the orienting netq'ork has been describcd by Fuentes(2004). with sufficiently long intenals betwccl thc prcscntation ofa semantically rclated prime and tal€et (Neely, 1977) or thc prcscntation of a semantically unrelated cuc bctwccn primc and target (similar to the double cue procedure), negativc priming \\'as obsen'ed.Taken together with the results P R O B I NTGH EM E C H A N I S MOSFA T T E N T I O N 415 Superior pa.ietallob6 Posterior Ternpofoparietal junction Frontalarea Figure 18.1. This fi gurc il lustratesbrain arcas involved in three attention ne1$,orks. The alelting network (squares)includcs thalamic and cottical sites relatcd to the brain'.srcrepinepherine system. The orienting nelwork (circles)is ccnteredon parietalsitcs (discussed section)and thc executivenetPrefrontal in thefblloqing (Triangle.tincludc. the Jnler.inr. ingucortex rtork latc and other frontal :rrcas, Thaamus I nterting O Orienting Executlve from studies (described above) examining ho\\, orienting and executiveattention co-act whcn primes or llankers arc presented at locations subjcct to IOR the bias for novelty "a sccms to be pcrvasivepropefiy of the attention system" (fucntes,2004). As indjcated above cognitive thcories of attention continue to b(] essentialin understanding attentional phenome n i r .i n l h e e r a o l n e u m e t h o d s . u L ha s n c u r o i m a g i n g . rvhich thev operateit is useful to scparatethe presentation of a cue indicating rvhcrc a target ."^,,ilJ occur from the prescntation of the target requiring a responsc(Posner,1980; Corbetta& Shulman, 2002).This methodolo5- has been used for behaviorzrlstudies q'ith normal people (Posner, 1980);patients (Posner,1988) and monkeys (Manocco & Davidson,1998);and in studiesusing scalp electrical recording (Hillyard, DiRusso & Martincz, 2004) and event reiated neuroimaging (Corbctta & Shulman 2002). Studies using cvent related fMRI have shown that folANATOMTCALNETWORKS lo\\,ing thc presentation of thc cuc and before the target is In this sectionwe oudine studiesusing all of the methods presented a nctwork of brain areas bccome'active (Corcitedr'Dourhistoricalintroductionto indicatethe common betta & Shulman, 2002; Kastner ct al., 1999; Hillvard, anatomv and circuitry of attentional networks involved in DiRusso, & Mal1inez, 2004). These include the superior alerting, oricnting, and executivecontrol. These arc illus- parictal lobe, temporal parictal junction and frontal eye trarteclin cartoon fbnn in Figure 18.1. 6elds shown in Figure 18.1.There is uidespread agreement about the identity of theseareas(sec Orienting areas in Figure 18.1)but there remains a considerableamount ORIENTING T O S E N S O R YE V E N T S of u'ork to do in order to understand the hrnction of cach Thc vastmajoriLyof studiesof the physicalbasisof atten- area. tion have involved orjenting to scnsoryevents,palrticularly When a target is presentedat thc cued location it is pro, visual events. The fi:-rdingsof Lhcsestudies pror,,idethc cessedmore efficiently than if no cue had been presented. basis fbr our limited understanding of how to approach I h e b r a i na r e a si n f lrr e n c e db 1o r i e n t i n gu i l l b e t h o . ew h i c h brain mechanisms of attention. In this field a basic dis- that would normally be those used to process the target. tinction is betwccn those brain areas that arc ilrfluenced For examplc, in the visual system orienting can influcnce b,yacts of orienting\(sitcs) and those that are parts of thc sitcs of processing in thc primary visual cortcx, or, or in orienting netrl,ork iisclf and thus the sourcesof the oricnt- a \ariety of extra striate visual areas ',vhcrc the computaing inlJuence.Although our discussion focusesmainly on tions relatcd to the target are performed. Orienting to tar, visior-r,it is limited to the sourccs of the attention effect get motion influencesarea MT (V5) while orienting to tarthat appear to be similar in other modalities (Macaluso, get color u ill inlluencc area V.l (Corbetta ct al., 199 1). This Frith & Driver,2000;Driver,Einer, & Macaluso,200,1). principle of activation of brain areasalso extendsLoh igher levcl visual input as u'cll, for example, attcntion to faces Sitesand sources,Normally all scnsory eventsact both to modifies activitv in the face sensitivearea of the fusiform contribute to a statc of alcrtness and to orient attcntion gytts (Wojciulik, Kanwisher, & Driver, 1998).The finding (Hcbb, 1949).In order to distinguish the brain areasthat that attention can modif] activity in primary visual areas arreinvoh'ed in orienting (SeeFigurc 18.1) from the sitesat (Posner&Gilbcrt,1999)hasbeenof particularlyimporrant 416 because thc microcircuitry of this brain area has been more extensivelystudied than another other Whcn multiplc targets are presentedthey tend duppress the normal level of activity they u,ould have produced if presented in isolation (Kastner et al., 1999). This finding has become the cornerstone of one of thc most popular views of attention in which emphasis is placed on compctition betwccn potential targetswithin cach relevant brain area (Dcsimone& Duncan, 1995).This view placesless stress upon top-dou'n control or at least emphasizesthat top-do$'n control emcrgcs from bottom-up competition. Functional anatomy. work with stroke patients showed that lesions of many brain areas result in difFculty shiliing attcntion to locations or objects that were conveyed dircctly to the damagedhemisphere(Rafal,1998).In ncurology thesc patients $'ould be said to be suffering from exaiDctionin that when simultaneousstimuli are presented to both hemispheresonly the one goingto the undamaged hemisphere is consciously perceivcd. Experimental studics suggestedthatwe could define different forms ofcxLinction due to lesions of thc parictal lobe, the midbrain or the that thalamus(Posner,1988).Data in the 1980ssuggested operations ofdisengage(parietal lobe),move (superior colliculus), and engage(pulvinar) were computed in different brain areas that formed a verlical network that together pcrformed the task of orienting. More recent studies involving both patients and imaging seem to sllpport this general approach to localization, but suggest somewhat different separation of thc operations involved. A paradox of thc lcsions studies ofthe early 1980su'as that the superior parietal lobe seemedto be thc ar:eamost related to producing a dif6culty in disengaging from a current focus of attention. Yet most clinical data sccmed to support the idea that clinical extinction arose frorri more fiom lcsions of the temporal-pa-rictaljunction. -Event related imaging studies have servedto reconcile this difterence(Corbetta& Shulman,2002).Thereseemto be two separateregions both of which can both produce difficulty in shifting attention in contralesional spacc,but for quite different rcasons. Lesions of thc temporal-parietal junction are important $'hen a novel or unexpectedstimulus occurs (Corbetta & Shulman, 2002; Friedrich et al., 1998;Karnath,Ferber,& Himmclbach,200l).When functioning nonnally, this area allou's disengagingfrom a current focus of attention to shift to thc ncrv event. This area is most critical in producing thc core elementsof the syndrome of neglect or extinction in both humans and monkeys although the exact location of the most critical area may differ bctween the two specics.In addition, therc is much clinical evidencethat in thc human there is latcralization in the right temporal parietal junction that ma-ybc more imporlant to thc dcficit than the left (Mesulam, 1981; Perry & Zeki, 2000). A diffcrcnt region, the supcrior parietal lobe, sccmsto be critical fbr voluntary shifts of attcntion following thc cue. In onc event-relatedfMRI study (Corbetta et al., 2000) this RUEDA,& KANSKE POSNER, rcgion was active follorving a cue informing the person lo shift attention covedly to the target. The region is part of a largernetwork that includcs frontal evefields and thc supcrior colliculus that appearsto orchestrateboth covert shift of attention and eye movements to\{ard targcts (Corbetta, 1998).When people voluntarily move their attention from Iocation to location while scarching for a visual targel this brain arca is also active. Therc is cvidence from other patient groups indicating brain areas involved in shifting attention. For examplc, patients with Alzhcimers diseaseinvolving degcncration in the superior parietal lobc (Parasurrnanet al., 1992)havc difiiculty in dealing with central cucs that inform them to shift their attention. There is also evidencc that lesions of the superior colliculus may be involved in the preference for novel locations rather than locations to u'hich one has already oriented (Sapir et al., 1999).Patients with lesions of thc thalamus (most likely thc pulvinar) also show subtle dcficits in visual-orienting tasks that ma-ybe related to the accessto the ventral information-processing strcam. It secms that a vertical netq'ork of brain areasrelated to r,oluntary eyc movements and to proccssing novel input arc critical elementsof oricnling, but a precisemodcl including a role for all of these areas is still lacking. It is also necessaryto reexamine thc role of alerting in the cueing effects.Thcre has been a great deal of evidence that damage to the right frontal lobe and to the right parietal lobe can producc difficulty in maintainilg the aleil state(for a summary seePosner& Petersen,1990).Hou' errer,rccent rvork with fMRI has indicated that using a cue to rvarn a subject that a target will occur shortly activatcsa IefthemispherencLwork(Coullet al., 1996;Coull,Nobre,& Frith, 2001;Nobrc, 2004).Thus there arc apparentlyroles for both the right a left hemispherein the alerting process. It appears that right hemisphere centers are most imPortant for tonic alertncss,but the left hemis;lhcre areasma1play a morc important role in phasic alerting produccd b,v rvarning signals. Circuifry. Cellular studics have shown that attention loward the location of an impending targct caD alter the baselineof cellular activity (Desimone& Duncan, 1995). This finding suggeststhat cuing attention to a location can induce changesin the visual system that altar the processingof a targct. Evidence flom high-density electrical activity suggeststhat cuing attention influenccs prcstriate activity occurring 100-150 milliseconds after input. This information may in some circumstances then be fcd back to influcnce activity within the primary visual cortcx and perhaps also the thalamic rela,vsof the visual information (O'Connoret al.,2002). Thesestudiessuggcsta circuitry by rrhich parietal activity can influence the visual analysis ofa visual target, but direct cvidcnce linking the morc dorsal attention system wilh the more ventral objcct analysis system is still lacking. The study of visual orienting has provided strong evidcnce that scalp recording can give an accurate time P R O B I NTGH EM E C H A N I S MOSFA T T E N T I O N course for the operation of gcncrators found active in fMRl studies. Hillyard and associates(Hillyard, DiRusso, & Ma*inez, 2004) have exploited the fact that early visual areas are retinotopically organized. They have identified an early ERP component (Cl) with the primary r,isualcortex operation at 50 or so milliseconds after input, theyhave sho\\,n lhat postcrior Pl and Nl arise in prestriate arcas. This rvork has led to the interesting finding that a cue to location does not influence the initial Vl activity but is fed back to in{luencelater striatc cortex component (Martincz el al.,2001). It is likcly thaL rvc still do not have the 6nal answcr as to tlle exact operations that occur at cach location even in a relatively simple act like shifling attention to a novel event. Nonetheless,the data provide considerablcconvergence bet\{'eenclinical, ncurophysiological, imaging and cognitivc methods. The results of attentional studics as u'iLh many othcr arcas of cognition supporl the general idea of localizationof componentoperations. Transmitte6. It is very imporlant 1() be able to link the neurosystem results, that suggest brain areas related to attention, u'ith cellular and synaptic studies that provide more details as lo thc local computations. One strategyfor doing so is to sludy thc pharmacology of each of the attcntion netrvorks (Marrocco & Davidson, 1998).To carn' out these tests it is important to be ablc to sludy monkeys rvho are able to use cues to direct attention to targets. Fortunately cueing studies can be run successfullyin monkeys. A series of pharmacological studics with alert monkeys havc rclatcd each of thc attentional netrvorksu'c havc discussedrvith specificchemical neuromodulators (Davidson & Man'occo,2000;Marrocco& Davidson,1998).The component of alcrt ing rclatcd to the influence ofu'arning signal appcars to invoh,e the cortical distribution of thc brain'.s norepinephrine (NE) systemarising in thc locus coeruleus of thc midbrain. Drugs like clonidine and guanlacine that act to block NE, reduce or eliminate the normal effcct of rvarning signals on reaction time, but havc no influence on orienting to thc targct location (Malrocco & Davidson, 1998). Cholinergic systems arising in the basal forebrain play a critical and jmportant role in orienting.LesioDsof Lhe basal forcbrain in monke-ysinterfere l,vith orienting attcntion (Vor,tkoet al., | 994). However it docs no1appear that the site of this effect is in the basal forebrain. Instead it appearsto invoh'e the superior parietal lobe. lnjections of scopolamine directlv into the lateral interparietal area of monkcl's, a brain area containing cells, which are influenced by cues aboul spaLial location, have been shorvn to have a largc effcct on the abilitl' to shift attention to a target. Systcmic injections of scopolamine havc a smaller etfect ori e1Tecton covert orienting of attention than do local injections in the parietal area (Davidson& Marrocco, 2000).Cholinergic drugs do not affect the ability of a lvarnjng signal to improve performance and thus there appcars to be double dissociation that relates NE to the alerling 417 network and Ach f.i,;t.h.f,""1 to thc orienting network. These obsenations in thc monkey have also bccn confirmed by similar studies in the rat'(Everitt & Robbins, 1997)and by studicsof nicotinein humans.Of specialsigniicance in the rat, studies comparisoni ofthe cholinergic and dopaminergic mechanisms have shown that only the former inJluencethe oricnting response. The evidcncerelating Ach to the oricnting network and NE to the aier.ting network provides strong evidencc of dissociationbetweenthe different attentional nctu'orks. ln the next sectionlve show tbat the frontal executivcnetrvork is closelyrelated to dopamine as a neural modulator. EXECUTIVEATTENTIONNETWORK E r c c u l i v c c o n t r o l i s m o s t n c c d c d i n . i t u a t i o n sw h i c h situations, which involve planning or decision-making, crror detection,novel rcsponses,arndin overcoming habitual actions (Shallice,1988).Although theseconceprsare somewhat vague, a morc explicit versiolr of the idea of executiveattention stressesthe role of attcntion in monitoring conllict between computations occuming in different brain arcas(Botvinicket al.,2001).Althoughthis vicw may not be adequateto explain all of the existing data, it provides a useful model for summarizing much of u'hat is known. Functional anatomy. A very large number of ftrnctional imaging studies have examined tasks that involvc executivc attention. These"thinking" tasksoften activate a wide range of frontal areas.For example, (Duncan et al., 2000) examined verbal, spatial and object tasks selected from intelligence tests that all had in common a strong loacling on the tbctor of general intelligence (g). Thcsc itcms lvere contrastedwith pcrccptually similar control items that djd not rcquirc the kind of attention and thought involvcd in problem solving. This subtraction led to differc!rial .lctiv, it]' in two maior areas.One rvas the anterior cingulate and the secondwas lateral prefrontal cortcx. Moreover,manipulations ofthe contcnt of matet-ialhavc often shown lhat the same areasmay be active in.cspcctive oflvhether the stimuli are spatial, verbal, or visual objects. This has led some to conclude that the frontal lobes may be an exception to the specilic identification ofbrain areas with mcntal operations that u,c have discussedfor oricnting (Duncan& ONen,2000). A specificcomparison of thrce conflict tasks $,ithin one study (Stroop, spatial conllict, and flankcr) shou'ed tuo areasof common activation bv thc three tasks (Fan ct al., 2003). These wcre thc anterior cingulatc and a left lateralized area of thc prellontal cortex (arca 10). A summar \,* of many imaging studies using the Stroop task or variants of it that involved conflict among elements (Bush, Luu, & Posncq2000)showedconsislcntaction in the dorsalanterior cingulate. An event-rel.rtedftrnctional MRI study of the Stroop effect used cues to separate presentation of the task 418 instruction lrom reaction to ahe target (li'cnonald et a1., 2000). Lateral prefronLal a.eas were responsive to cues indicating u'hether the task involvcd naming the rvord or dealing with the ink color. The cue did not activate the cingulate. When the task invoh,'ednaming thc ink color the cingulate was more active on incongrLlent than con, gment trials. This rcsult reflects the general finding that lateral areasarc involved in represcnting specificinformation over timc (working memor-v),whereas medial arcas are morc relateclto the detection of conJlict. Another cue to thc functional activitv in these areas comes from studies of generating thc use of a word. In a typical version of this task, subjectsare shown a seriesof forty simple nouns (e.g.,hammer) (Raichleet al., 199,1). In the experimcntalcondition they indicate the use of each noun (for example, hammcr -> pound). In the control conclition, they simply rcad the rvord aloud. Thc diffcrcnce in activation bctween the two tasks illustrates *hat happens in the brain when subjccts are required to develop a very simple thought, in this case how to use a hammer Practicc that is sufficient to automatize the responsesresults in eliminating the activation of the anterior cingulate and lateral arcas,but increasesacti\,ity in the anterior insula rvhich is active during word reading, but reduccd during generating a new use. These results illustrate that the anatomv ofthis high-level cognitive activity is simi)ar enough among individuals to prodlrce focal average activations that are both statistically signi6cant and reproducible. 'fo Circuitry. examrnethe time course of thcse activations it is possible to use a large number of scalp electrodesto obtain scalp signatures of tbe generators found active in imaging stuilis.\(,lbdullaev & Posne41998).When subjects obtain the usc of a noun, there is an area of positivc electrical activity over frontal elcctrodesstarting abollt 150 milliseconds after the rvord appears.This early clcctrical activity is generated by the large area of activation in the anterior cingulate. A lcfL prefrontal area (antcrior to the classical Broca's area) begins to show activity about 200 milliseconds after the word occurs. This area appears to be activated when the task involves a semantic content, but the early time course of the activation and its closerclation to thc cingulate seem to make it more related to attention to scmantic content. The lcft posterior brain area found to be more active during the processingof thc meaning oft isual words did not appearuntil a much later time (500milliseconds). This activity is near the classical Wernicke'sarea; lesions of which are knou'n fo produce a ioss of undcrstanding of mcaningful speech.An examination ofcorrelations among distant electrodesshowed evidenceofthe transfer of infor, mation from left fi'ontal electrodcs to the posterior area a1 about 450 milliseconds into the task (Nikolaev et al., 2002).Becausethe response time for this task was about 1,100millisecondsthis would leavetime for the generation of relatcd associationsneededto soh,ethe task. POSNER R,U E D A&, K A NS K E Thesestudies provide a stan in understanding the functional rolcs of different brain areas in carrying out cxccu, tive control. The medial llontal area appearsmost related to the executivcattention network and is activewhen therc is conllict among stjmuli and responses.It may be scning as a monitor of conflict, but it is possible that it plays other rolcs as well. The latcral prefrontal area scems to be important in holding in mind the information relevant to the task. Even $",hcna single item is presented,it may still be necessaryto hold it in some lemporary areawhile other. fwhereas is not correct while means at the same time as] brain areasretrier,,einformation relevant to thc response. Togethcr.these two areas arc nccded to solve nearlv any problem, that depends upon attention to thc rctrieval of stored information. Both of thcse areascould be said to bc rclated to attentioD, or one might identifu only thc medial area \\,ith attention and the lateral one u'iLh r"'orking memor!'. In cithcr case they begin to give us a handle on hor.r' the brain parseshigh tasks into individual operations that are carried out in separateparts of thc network. Lesion studies. Classical studies of strokcs of thc frontal midline including the anterior cingulatc shou'ed a pervasive deficit of voluntary behavior (Damasio, 199,1; Kennard, 1955).Patients',vithakinetic mutism can orient to external stimuli and follow people wilh thcir eyes, but thcy do not initiate voluntary activity. Recent studics of patients r.vith small lesions of the anterior cingulate (Ochsner et a[., 2001; Turken & Su,ick, 1999) show defrcits in conflict related tasks, but thcsc patients frequently recover from their deficits suggesting that other areasmay also be invol!'ed.In somc caseslesionsofthe mid frontal area in children and adults may producc pcrma nent loss of future planning and appropriate social behav ior (Damasio,1994).Earlv-childhooddamagein this arca can produce permanent dellcits in decision making tasks that require responsesbascdon future planning (Anderson et al., 2000). Cellular mechanisms.The anterior cingulatc and larcral frontal cortex arc target areas of thc ventral tegmental dopamine system. All of the dopamine receptors arc expressedin layerfive ofthe cingulate, which in turn is connected to many other important cortical arcas (GoJdmanRakic, 1988). The associationof the anterior cingulatc u'ith high level attentional control may seem rather odd because this is clearly a phylogenetically old area of thc brain. Although the anterior cingulate is an ancjent structurc, there is evidencethat it has evolvedsigni6cantly in primates. Humans and great apes appear to have a uniquc cell type fbund mainly in layer V of the anterior cingulate and insula, a ccll t)pe not presentin othef primates(Nimchinskyct al., 1999).Thesecells also undergo a rather late dcvclopment in line with the fndings [hat executive control systems develop strongly during later childhood (Allman, 2001) (see also next section). Although the precisc function of P R O B I NTGH EM E C H A N I S MOSFA T T E N T I O N this cell is not known, high correlations betweenitsvolume and encephalizationsuggesta likely role in higher conical functioning. Thc proximity of these cells to vocalization ar-easin pi-imatesled Nimchinksy and colleagucsto specLllatethat thcse cells may link emotional and motor areas, ultimately rcsulting in vocalizations that conveyemotional mcaning. There is as yet no dircct evidence linking the cellular archilecture of the anterior cingulatc to activity d e r e c t e d t r r i n gn c L r r o i m . g i n*gru d i e s . Several repiicated human genetic studies demonstrate an association of one of the dopaminc feceptor genes D.4 (DRD4) located on chromosome 11p15.5 and an attenlional disordcr common in childhood (attention dcficiL/hlperactivity disorder or ADHD) (Swanson et al., 2000).About 50,/oof the ADHD caseshave a 7-repeatallele whcrcas onl-vabout 20% ethnically matched control subjects have a 7-repeat allele. However,a direct comparison of children with ADHD ',vho either havc or do not have the 7 repeat allele suggestthat attentional abnormalities are morc common in those children rvithout the 7 repeat (Su,ansonet a1.,2000).The authorssuggestthat thereare diffcrcnt routcs to ADHD onlj' some of which involve a specific reduction in cognitivc ability. I N D I V I D U A LD I F F E R E N C E S Although there is strong evidence of common networks underlying cognitive proccsses,there are also individual differences in details that inJluencethc cf6ciency of these net\\,orks. Individual differenccs arc likely to reflect both genes and expcriencc. The rapid development of fMRl methods has bcgun to provide a basis for understanding differencesamong individual brains both anatomically a]!d in terms of functional activations. These differenccs are to be expected becausc pcople are not identical in thcir thoughts, feelings,or behaviors.Scvcral studies have , shorvn that individrral differcnces in functional activation (Miller et al., 2002;Reiss,Backus, can be reliablyasscssed & Heeger,2000). To study thcse individual differences an attention nel\\'orks tcst (ANT) has been used to examinc thc emciency of the three brain netr,vorksu'e have describedin the previous section(Fan et a1.,2002). As illustrateclin Figure 18.2 the test provides Lhrcc scores that represent thc skill of cach individual in the alerting, oricnting, and executive nch.vorks.In a s:rrnpleof .10normal persons cach of these scoresrvere reliable over repeatcd presentations. The ability to mcasure differences in attention among adults raiscs the qr.restionof the degreeto \,hich attcntion is heritable. In order to dcal r.vilh lhis issue,the attenrion net\\'ork test was used to strrdy 26 pairs of monozygotic and 26 pairs of dyzygotic same sex twins (Fan, Fossella, & Posncr,2001). Slrong correlations betwccn the monozygotic twins for the executivenetwork, lcd to an estimate of heritability of thc cxccutil'e network of .89. Becauscof the small sample, the estimate of 95'l" conlidence interval for heritability is between .3 and .9. In lact a more recent study 419 congruent incongrueni neutral E[IE nocue centercue doublecue t l t l + . l l spararcue Figure 18,2. A schematic of the Attention Nctwork Test. The task requires a left key press u'hen thc central arorv points lefi and a right keyprcss rvhen it points right. The arrow is surrounded by Ilankersjs pointing in thc same (congruent) or.opposite clirection (incongruent). Before the targct cues inform the person of \\,hen and rvhcrc a target $ill appear. At the bottom of tlc figure are three subtractions thatyield infotmation on the efllciency ofthrcc altentional netucrks.. (Adapted from Fan et al., 2002). using a somewhat different task has fhiled to shor.vheritability among children rvith the flanker task (Stins cL al., 2004), although they did find substantial heritabilitv u'ith another executiveattention task, the Stroop task. Possibly this discrepancyrelateclto the importance of etrors in thc child data. Nonetheless,these data overall support a role for gencs in executiveattcntion. ','The Attention Network Test (ANT sed Figurc 18.1) has b e e nu s e dt o e r a m i n ec u n d i d . r tgee n e rr e l a l ( . dl o c h e m i c a l neuromodulators of attentional netu,orks. Alleles of tr.vo: cholinergic gcnes have been found to inlluence a visual , scarchtaskrelated to thc orienting network (Parasuraman, Greenrvood, Kumar, & Fossella, 2004), rvhereas alleles of several dopamine genes influencc perfbrrnance in the flanl<cr |ask and when compared produccd a significant diffcrence in activation in lhe anterior cingulate (Fossella et aI 2002: Fan et al., 2003). Allclcs of additional gcne (COMT) have been found to relate to a different conflict relatcd phenotlpe (Diamond ct al., 2004). 420 Studics have also examined the role of genetic differcnces in the strength of activation of nct,,r'orksinvolved in attentio| and memory in fMRI studies (Mattay & Goldberg, 200,1).These studies demonstrate that at least part of thc variability in strength of activation is due ro having dilTerent versions (alleles) of genes related to the network. Gcnetic differences obscr-vedto date account for only a small part of the variance found in bchavior and imaging. Horvever,a major co[tribution of these differcnces is that they servc as clues to the genesinvolvcd in network development. Thesegenescan be examincd in comparative animal studies to addressqucstions like how genesrclated to hippocampal developmcnt mav have affected bchavior in specieser,,enbcfore there was a hippocampus. Thesegenes can also be examined in specicsfor ruhich the hippocampus plays arole in forms of mcmory that maybeprecursors of the explicit recollection fbund to be iLsrole in humans. ln the case of the DRD4 gene,which in humans is related to attention deficit disorder(Swansonet aI.,2000)and to the normal monitoring of conflict in the mouse, sccms to be relatcd to cxploration of the environmcnt (Grandy & Krlzich, 2004; Han, Touathaigh, & Koch, 2004). These studies have the potential of improving our understanding of the role of genes in shaping the networks common to all humans. POSNER R,U E D A&, K A N S K E and the accuracv of termination continue to improve in Iatc childhood. The ANT involvesavery simple senseoforienting to visual localions that uses the ability of a periphcral cue to redirect attention to one of two placcs above and below firation and therefbre,would appear to be a task u'hose requirements would suggestal early developmental coursc. Most of the work in this area, including dcvclopmental studies summarized by Trick and Enns (1998) comparcsvalid and invalid cuc conditions (cost plus benefit) and thus provide stronger evidenceofthe time to disengagcand reorient from an attendedlocation. Studics madc under conditions whcrc orienting involved an invalid cuc and thus requircd a voluntary shift ofattcntion have sho\r,n that the timc to disengagefrom a cucd location is reduced wilh age,but the movemcnt of attention toward a pcripheral cue shows no changebetu,eensix year olds and adults (Akhtar & Enns, 1989).They also found that chilclrenshorv a strong tendencyfor an intcraction betweenorienting ard conJlict that is reduced between 5-year-oldsand adr.rlts. Alerting During the first year of life, children show a remarkable developmentof their ability to achieve and maitrtain alert states. Howevcr, Lhere are still considerable dillerences between children and adults in both spccd of preparation from alerting cues and maintenance of that preparation (Morrison, 1982).Both preparation and vigilancc might be Gene by environment interactions. One reasonfor thc rel- playing a role in the difTerencesfound in arlertnessamong alivcly modest eftect of genetic alleles in accounting for children and adults in the child ANT study Thcse phabehavioral differencesmay be that they interact rvith expe- sic and tonic aspectsof alerlness may inllucncc RT $'hen ricncc during development of the nctwork. The existence alertnessis measured by comparing trials $'ith and uithof gene by environmcnt interaction is not controversial, out waming cues.Age differencesin preparalion certainly and it is r.vcll known that gene exprcssion can be influ- affect RT to cued trials, q'hereas diffcrcnces in vigilance enced by the microenvironment in the brain area where it might affect non-cued trials. is cxpressed.Moreover,there is ample evidencethat in priA study by Berge!, et al (2000) showed that S-year-old matcs, geneexpressioncan be influenced by events,thich, children reducc their reaction time to stimuli that are prelike rnaternal scparation, can be a part of human devel- ceded by an alert cue although, unlike the adults, chilopment (Soumi, 2003). These findings make more impor- dren showed reduced RT bcnefits with cue-target intertant the examination of how attentional networks actually vals greater than 500 ms, suggesting increased difficulty developduring infancy and childhood, a topic to which we forchildren to maintain preparation produced bythe alertturn in the ncxt section. ing cue. Moreover,young children have increaseddilficult1 compared to older children and adults rvhen dealing rvith situations that require more complex strategiesto prepare, DEVELOPINGNETWORKSOF ATTENTION as uhen the interval between the alert cue and thc targct A study using the child version of the attention nctwork varies acrosstrials. test (Rucda et al., 2004), examined thc dcvelopment of the On thc other hand,Lin, Hsiao & Chen(1999)examined attentional netu'orks in a cross-sectionalstudy involving sustained attention abilities in 6-15 year-olds using the 6-10-vear-old children and adults. Results indicated no Continuous Performance Test (CPT).They found progreschanges in the orienting scores in the age range studied, sive improvement in pcrformance (measured by hits and rvhereas alcrtness showed evidence of change up to and false alarms) with age, reaching asymptotic levels arouncl bcyond age 10. Executivc attcntion measured by conJlict age 13.The percentageof childrcn that completethe CPT resolution scorcs appeared stable after age 7 up to adult- at preschool ages is informative of their ability to sustain hood. Thesc findings are placed in context below. attention. Levy (1980) found that lessthan 50"/oof the chil, dren between 3 and 4 years of age $'ere ablc to complete Orienting the test,whereasthe percentageincrcased to 70,/ofor chilStudies of orienting summarized in Ruff and Rothbart dren betwcen 4 and 4 and a half ycar-olds and was close ( 1996)have suggestcdthat only voluntarn movement speed to 10070after that age. P R O B I NTGH EM E C H A N I S MOSFA T T E N T I O N The influence of phasic and tonic components on the ef6ciency of alertnesshas been compared bctrveen6 and l0 year-olds and erdults(Rueda et al., in process).In this e{perimcnt, participants performcd 4 blocks of trials of a Go/No-Gotaskrvith a low percentage(25%) ofGo trials. To examine differencesin phasic alednessthe presence(75rlo of the trials) or abscncc (.25a/a of the trials) and the time intcr-val(simultaneous,short, and long) betweenthc lr'ar-ning cuc and the target were all manipulated. Compared to trials rvith no warning cue, children and adults showed rccluced RT to targcts prcceded by a cue, but only adults shorved reduced RT whcn cue and targct were presented simultancously. In this experimcnt, both 6- and 10-yearold children showed a continuous increase in RT across blocks, whereasadults had equivalent RTs in all blocks. In addition, 6-year-oldchildren showcd greaterpercentagcof omissions than 10 year-olds and adults. lnterestingly, this d i F l e r e n crc, , a .s i g n i f i c a not n l v u h c n n o w a m i n g c u c ' , r a . prescnted or \,"'hencue and targct were presentedsimultaneoush; whereas no age differenceswere found when the waming cue preccded the target, cspecially at long cuetarget intervals. Taken together,thcsc results suggcstthat children seem to have grcater difficu)ty than adults sustaining attention during extended task performance. This difference appearsto be more remarkable for voung children, although their reduced vigilance can be ovcrcome by presenting u'arning cues with some time in advance. Thc inf'luenceof rvarning signalson performancemay varl rvith age becauseof the greater difficulty children have in retaining the set toward task instr-uctions. 421 Although 2-year-old children tended to perseverateon a single response,3 year-olds performed at high accuracy levels, although, Iike adults, they responded more slowly andwithrcducedaccuracyto incompatible trials (GerardiCaulton,2000;Rothbart et al.,2003). Thc detectionand correction of errors is another forrn of action monitoring. While perlbrming the SCT, 2 1/2 and 3-year-old children showed longer RT following erroneous trials than following cor-rectones, indicating that children were noticing their errors and using them to guide performance in the next trial. Houevcr, no evidence of slor,"'ingfollorving an error was found at 2 years of age (Rothbart et al., 2OO3). A similar result with a different time llame rvas found rvhcn using a version of the Simplc Simon gamc. In this task, children are asked to execute a response u,hen a command is given by onc stuffed animal, rvhjle inhibiting rcsponses commanded by a sccond animal (Jones, Rothbart, & Posner,2003). Children of 36,38 months \.vcre unable to inhibit their response and showed no slor.r,ing following an error, but at 39-"41months, children shou'ed both an ability to inhibit and a slou,ing ofreaction rime following an error Theseresults suggcstthat betwccn 30 and 39 months children greatly develop their ability to detect and correct erroneous responsesand that this abilit), mav relate to the developmentof inhibitory control. The importance of bcing able to study the emcrgence of executiveattcntion is enhancedbecausecognitive measures of conflict rcsolution in thesc laboratory tasks have been linked to aspects of children's temperament. Signs of the development of executive attention by cognitive tasks rclate to a temperamcntal measurc obtained from Executiveattention caregiverreports callcd effortfu 1control (Gerardi-Caulton, The finding of little or no development in the execurive 2000; Rothbart, Ellis & Posner,2004). Children rclativelv nctu'ork afier age 7 in the child ANT study may not extcnd lessattectedby conflict receivedhigher parental ratings of to morc clifficult executivetasksas thoseinvolving stratcgic temperamental effonftll control and higher scorcs on labdecisionsor othcr functions like rule-holding, planning, set oratory mcasures of inhibitory control (Gcrardi-Caulton, su'itching, and so on. Houever, developmental studies of 2000). We regard effonful control as refJecting thc effi, cxecutive attention have shown the greater development ciency with which the executjve aLtcntion network (rperof conllict resolution to happen bet\\'een 2 and 6 years of atesin naturalisticsettings. agc (Rucda, Posner,& Rothbart, submitted). Empathy is strongly related to cffodful control, q,ith Infant studies have stressedthc relative lack of execu- children high in effortful control showing greatcr empathv tive control during the first year of life (Ruff & Rothbart, (Rothban, Ahadi, & Hershey, 1994). To display cmpathv 1996).Horvever,a sign of the control of cognitive conJlict towards others requircs that we intcrpret their signals of is found aLthc ond of the first year of lifc. Inferntsvoungcr distress or pleasurc. lmaging rvork in nor-rnalsshows that than 12months fail to searchfor an object hjddcn in a loca- sad facesactivate the amygdala.As sadnessincreases,this tion $'hen previously faincd to reach for the objcct in a activation is accompaniedby activity in the antcrior cingudifferent locaLion.After the first year,children developthe late as pan of the attention net\\,ork (Blair et al., 1999).lt ability to inhibjt the prepotent responsetoward thc rrained seemslikely that the cingulate activity represcntsthe basis location, and successfullyrcach for the object in the nerv for our attention to the distrcss of others. location (Diamond,1991). Developmentalstudieshave identified different routes to From two years of age and older, children are able the successfuldcvelopmentof conscience.The internalizato perform simple conflict tasks in which their reaction tion of moral principles appears ro be facilitatcd in feartimc can be measured. The Spatial Conflict Task (SCT; ftrl preschool-agedchildren, especially rvhen their morhGcrardi-Caulton, 2000) induces conflict between thc iden- ers use genlle discipline (Kochanska, 1995). A stronglv tity and thc location of an object. Betwccn 2 and 4 years of reactivc amygdala would provide thc signals of distress agc, chilclren progressedfrom an almost complete inabil- that would casily allow empathic feelings toward others ity to carrl' out the task to relativcly good perlbrmancc. and improve socialization abilities. ln the absencc of this 422 forrn of control development of the cingulate wouJd allow appropriate attention to the signals provided by amygdala activity. Consistentu'ith iLsinfluence on empathy effortful control also appears to play a role in the developmcnt of conscience. In addition, internalized control is facilitated in children high in effortful control (Kochanskr et al., 1996). Thus, two separable control systems,one reactive (fear) and one sell-regulative (effortful control) appear to regulate the devclopment of conscience. Some developmentalstudies have bcen car-riedout using ERPSand conJlict tasks aimcd at understanding the brain mecbanisms that underlie thc development of executive attention. In onc of these studies, a flanker task was used to compare conflict resolution in thrcc groups of children aged 5 to 6, 7 to 9, and l0 to 12, and a group of adults(Riddcrinkhof& van der Molen, 1995).In rhissrud): dcvclopmental dillerences were examincd in t\\,o ERP components, onc rclatcd to response preparation (LRP) .rnd another one related to stimulus cvaluation (P3). The authors found differenccs betr.veenchilclren and adults in the latcncyofthe LRP,but not in the latencyoftheP3 peak, suggestingthat developmentaldiffcrences in the ability to resist iDterfcrcncc are rnainly related to responsecompetition ard inhibition, but not to stimulus evaluation. In adult studies, the N2 has been related to situations that rcquire executivecontrol (Kopp, Rist, & Mattle4 1996) and has becn dircctly associatedto activation coming from the antcrior cingulate cortex (van Veen & Cancr, 2002). We have recently conducted an ERP study in u,hich rre used the child-friendly version of the flanker task used in the child ANT study with 4-year-old children and adults (Rueda et al., 2004).Adults showed largerN2 for incongruent trials overthe mid frontal leads.Four-year-oldchildren also showed a larger negative dcflcction for the incongruent condition at thc mid liontal electrodesthat, compared to adults, had a largcr size, greater amplitude, and were cxtcndeclover a longer period of time. Whcreas the liontal effect u'as evident for adults at around 300 ms post'target, children did not show any effect until approximately 550 ms afier the target. In addition, the effect was sustained over a pcriod of 500 ms before the children's responses,in contrast with on]y 50 ms in thc caseof adults. The difJerence obsen'edbetweenchildren and adults overthe frontal cham-relsdiffercd ilom other components observedat mid pariclal channels. For both children and adults, u'c found a greatcr positivity fbr incongment trials over mid parictal leads.Foradults, this clfect rvasobser-vedat approximately 400 ms post-target, in the time window of the P3, whereas it was more delayed in the case of children (between 800 and 1100 ms post-target).This parietal effect could ref'lcct dcvelopmental differences in the difficulty of evaluating the display depending on the congrucncc of surrounding flankers, while the frontal effect could reveal differencesin the time course of conJlict resolutioIr. Another important difference between ,l-year-old children and adults was the distribution of cffects over the scalp.In adults, the frontal effecLsappcarto be focalizedon P O S N E R ,U E D A&, K A N S K E the mid-linc, whereasin children the effectswere obscn'cd mostly at pre-frontal sites and in a broader number of channels,including the mid-line and lateral areas.In addition, the effect on the P3 appearsto be left lateralized in thc adult data but lateralized to the right side in the children. The focalization of signals in adults as compared to children is consistent with ncuroimaging studies conducted rvith older children, where children appear to activate the same network of arcas as adults when perfor-rningsimilar tasks, but the averagevolume of activation appcars to be remarkably greater in children compared to adults (Casey et al., 1997;Durston et a1.,2002;Caseyct al., 2002).Altogether, these data suggestthat the brain circuitry underlying exccutive functions becomesmorc focal and refined as it gains in efficienc),.This maturational processinvolves not only greatcr anatomical specialization but also rcduc, ing the time thcsc systemsneed to resolveeach of the prcr ccssesimplicated in the task. ATTENTIONAL PATHOLOGIES Attcntion is a very frequent symptom of many forms of psychopatholog_v. However, $,ithout a real undcrstanding of the neural substratesof atte[tion, this has been a somewhat empty classi6catiot. This situation has been changed \\'ith the systematic application of our understanding of attentional networks to pathological issues.Viewing attention in terrns of u[derlying neura] netrvorks pror,'idesa mcans of classifJing disorders that diflers from thc usual DSM IV symptom rclated criteria. A number of abnorrnalities involving attention, including Alzheimer's dementia, anxiety, attention dencit hyperactivity disorder (ADHD), autism, bordcrline personality disorder, depression, and schizophrenia have been studied either with the attention nct$'ork task (Fan et al., 2002),that measurcsthe efficiency of all three networks (sce Figure 18.2)or u,ith parts of the task that measurc one or two of the netruorks.Thesestudies have shou'n that different disorders are associatedr,lith problems in diflerent networks, althou€h therc is not a ore to one relation between diagnosjs and disordex Belou' we revierva numberofcommon disorders in relation to abnormalities in attcntional networks. ALERTING Patients with anterior and posterior right hemispherc damagehaveproblems when tasksare given without war-ning (Posneret al., 1987;Robertsonet al., 1998).This ariscs becausepatients, like young children, havc ver 1-long RTs in the absenceof warning. Robefison has argued that the inability to maintain the alert state absent a rvaming signal is a major co[tributor to the reduced attention to the side of space opposite the lesion found more strongly in patientswith right than with left posteriorlcsions. A stLrdyusing the ANT has shown that normal elderly personsalso show dramatically larger alerting effccLsthan young adults, resembling what is lbund r.vith childrcn P R O B I NTGH EM E C H A N I S MOSFA T T E N T I O N (Fernanclez-Duquea "to.p, .i*)-p.*). The studv also found that the norrnally developingadults and Alzheimers patients sho\\,ed thc samc clevated alefiing scores, but only thc Alzhcimcrt paticnts showed increased difficulty in resoh'ing conflict (seeexecutiveattention section). ADHO. Studics of ADHD have linked the disordcr to aspectsof both attcntionand sensationseeking(Srvanson et al., 2001). Many theories of ADHD have suggesteda deficit in executivc firnctions (Barkley, 1997).Horvcvcr,in earlv r.r'orkusing a spatial orienting task, the most compelling deficit appeared to be a difficulty in maintaining the aleft state in the absenceof a warrring signal (Su'anson et al., 1991).This difficulty might arise from right hemisphere damage,rthich has also bcen rcported to be a feature in many studiesof ADHD. More recent studies using the ANT havc also shown problems u,ith aiefiing, again mostly due to the inability to hold the alert state when no uarning signal was used. In one study (Booth, Carlson, & Tircker, 2002), the ANT was used to attcmpt to discriminate the inattentivc subtypc lrom normals and the combined subt)pe. Thc alerting network best distinguished the different forms of ADHD, with inattentive children shorving lcss ability to maintain lhc alcn :tatc in thcabsenco e I w c r n i n gs i g n a l s . Neuroimaging studies ofADHD children have generally shorvn right lrontal, cingulate and basal ganglia deficits (Caseyet al., 1997).Becauseright Frontalareashave been related both to problems with the alert statc and with inhibitory control there could be links betwccn the AN-T rcsulls and thcsc imaging studies, but this research has not yct bcen conduclcd. Caseli Durston, and Fossella(2001) used thrcc diiTerent tasksthaLrclyupon differcnt proccsses(stimulus selection, responsc selection, and response execution) to analyze executive firnctions in differcnt types of developmental disorders (6chizophrenia, Sydenham'sChorea, Tourette's Slndrome, and ADHD). They slrggest that each of the cognitjve operations is implcmentcd in a particular basal ganglia-thalamo-cortical circuit. Stimulus processing scems to be related to connections betweenbasal ganglia, thalamus and the dorso-lateral prefrontal cortex, r,rhereas responseprocessingis associatedwith conDcctionsof subcortical structurcs to thc latcral orbital liontal cortex. Schizophrenic patients exhibited deficits in stimulus blcction, Sy'denhams chorea in response sclcction, Tourettei syndrome chilclren in responseexecution,and ADHD children in both stimulus selection and response execution, suggesting that specilic cognilile opcrations related to cxccutivc attcntion can be independently damaged. For a numbcr of ycars it has been thought that ADHD related to problems with dopamine and other catecholamind (Wender',1971).In molccular gcncticsresearch, the dopamine theory found support in rcplicated findings that one allele(7 repeat)ofthe dopamine4 rcceptorgeneis over-representedjn children with ADHD and also is associated r.r,itha temperament featuring high sensationseeking 423 (see Swanson et al., 2001 for a recent summary). Sensation seeking is a lower order construct of extraversion. This finding has been well replicated for thc syndrome of ADHD, but has not been found 1o produce a cognitive deficit in executivefunction (Swansonet a1.,2000). One study of children rvith and without the 7 repeat allele confirmed it is associatedwith ADHD, but sho',vcd that it was not associalcd $'ith the cognitive dcficit that usually accompaniesADHD (Swansonet al., 2000).This linding led to the suggestionthat there may be two routes to ADHD. One route ivould involve a temperamental extreme of sensation secking (or extraversion), the frequency of rvhich might be increasedby the presenceofthe repeat version of the Dopamine 4 receptor gene.This route need not -involvea cognitive delicit. A secondroute to ADHD r.vould involve cognitive deficits that might either be gcnctic, or due to earl-vbrain injury or other expericntial factors. ORIENTING Anxiety and depress/on-There is much new inforrnation explicating the rolc of attention in anxicty, depression,and mood disorders.In a seriesof studies,sub-clinicalcollege students $ith high scores on trait anxiety uerc cued to attend to a location by a positive, negative,or neutral face. Trials on which the cue to thc location was negativc and invalid produced longer reaction times for the trait anxiety subjects (Fox, Ricardo, & Dutton, 2002; Fox et al., 2001). Thesercsults replicate and cxtcnd previous studics by Dernbenl'and Reed(1994),and togcthcrthev suggesr that trait anxiety influences thc ability to disengageparticularly from threat stimuli. Derryberr] and Reed suggest that this frnding may be dependentupon relatively lorv 1er. els of effortful control. Thosesubjectshigh in effortful control but suffcring from depression did not have difficulty disengagingfrom ncgative affect. A s5rmptomofdepression is the tendencyto drvell on leg, ative ideation (Beck, 1976),Vaseyand Macleod (2001) have revievu'cdrccent studies on trait anxious children, finding cvidence for the children making threatening intcrprctations of ambiguousstimulusmatcrial,overestimalingthc likelihood of luturc negative events, and shorving a neg ative bias toward threatening information. Ncgative bias has also bccn noted in childrens speeding of detection of dot probes in the vicinitv of threatening $,ords (Bijrtcbier,1998;Schippelct al.,2003).ln temperamcntresearch, the ability to control attention was found to be negatir,.ely related to negative affect (Derryben1 & Rothbart, 1988; Rothbart, Ahadi, & Evans,2000),cong.uent with thc inrer, pretation that good attcntional mechanlsms may sen'e to protect against negative idcation. Children who havc hard a history of abuse have also been fbund to be hvpersensitive to the rccognition of angry faces,misclassilying objectively neutral faces as actually angry (Pollak & Kistler, 2002). Together these findings suggest that both tcmper, ament and expcricnce can influence aspects of attention to\,"'ard threat stimuli, perhaps by both enhancing the 424 boundary ofclassification and increasing the time to dwcll on these stimuli. Because orienting to cucs and targets can be studied in children lrom birth onward (Pollak & Kistlcr', 2002) it rvould be possible to usc thcse findings to obtain more information on the effect of anxiety on normal development and to determine the degree to rvhich it prcdict. leter problems,givenstrcssfulc,<perience. Thc brain systems related to unipolar depressionhave been cxplored in a number of imaging studics (Drevets& Raichle,1998;Liotti et al.,2003).Thesestudieshavegenerally shorvn the importance of midlinc frontal areasincluding the anterior cingulate and orbital pretsontal cortex. Jn normal persons these areas are related to the cxpcricnce and control ofemotion (Bush, Luu, & Posner,2000),behaviorand cognition (Drevets,2000),and self-image(Gusnard et al., 2003). The areas appear to function abnor-rnallyin depressed pcrsons exposed to material producing a sad mood, u'hether or not they were currently dcprcsscd.The overlap betrveen brain activities in currently depressed people with those who have suffered from depression in the past may explain thc frequent occurrence of multiplc depressivebouts. POSN ER,RUEDA,& KANSKE generalizationofresponding in the amygdala and reduced responding in the anterior cingulate and rclated midline frontal areas (Posneret al.,2002). Paticntswith higher effortful control and lower conllict scoreson the ANT u'crc also the most likely to show the effects of therapl. This methodology shou's the utility of focusing on the core deficits of patients, defining appropriate control groups basedon matched tcmpcramcnt, and using specifrcattentional tests to hclp dctermine how to conduct imaging studies. Schizophrenia.A number of ycars ago, never medicated schizophrenic patients wcre tested both by imaging and lvith a cued detection task similar to the orienting part of the ANT. At rest, thesc subjectshad shou'n a lbcal decrease in cerebral blood flort in the lcft globus palidus (Early et al., 1989)a part of the basal gangliau,ith closeties to the anterior cingulatc. Thc subjects showed a deficit in orienting similar to rvhat we had shown for left parictal paticnts (Early et al., 1989).When lhcir visual attention was cngaged, they had difficulty in shifting attention to the right visual 6cld. Horveve; they also showed deficits in conllict tasks, particularly when they had to rely on a Autlsrn. Autism is a disorder that has been linked to languagecue. lt was concludcd that the overall patter-nof the orienting system (Akshoomoft Pierce, & Courchesne, thcir behavior was most consistent u'ith a dcficit in the 2002; Laldry & Bryson, in press). It is well known that anterior cingulate and basal ganglia, parts of a fiontally ar.rtisticpersons do not normallv orient to faces.Howeve; based executivc al-tentionsystem.This deficit in orienting Landry and Bryson report their diffrculty in orienting in rightrvard has been replicated in 6rst break schizophrentasks that iwolve non-social stimuli similar to those used ics, but does not seem to be true later in the disorder in the ANT. Similar deficits in thc ability to disengageand (Maruff et al., 1995), nor does this pattern appear to be move attention have been rcportcd in autism in relation part ofthe gcnctic prcdisposition for schizophrenia (Pardo to abnorrnal developmcnt of the cerebellum (Akshoomoff, ct al., 2000). First break schizophrenic subjccts often have Picrcc, & Courchesne,2002).We do not know ifthis abnor- been shown to leave hemisphere deficits and there have malityis due only to cerebellardcficits becausemany ofthe been many reports of anterior cingulate and basal ganpaticnts also sho$' parietal abnormalities as well. Rodicr glia deficitsin patientswith schizophrcnia(Bcncs,1999). (2002) has some evidencethat the abnormalities found in It appcars that the anterior cingulate may be part of a autism might relate to a geneassociatedwith migmtion of much larger netrvork of frontal and temporal structurcs cells in ear)y development. that operate abnorrnally in schizophrenia (Benes, 1999). A recent study using the ANT cast some light on these results (Wang, et al., 2005) in this case the schizophrcnic EXECUTIVEFUNCTION patient were chronic and thcy u'ere compared rvith a simi Borderline, Borderline personality disorder is character- larly agedcontrol group. Thc schizophrenic patients had a ized by very great lability of affect and problems in inter- much greater dilficulty resolving conflict than did thc norpersonal relations. In some cases, patients are suicidal mal controls. The deficit with thcsc patients was also much v carry out self-mutilation. Bccausc this diagnosis has been larger than that found for borderline personality patients, studied largcly by psychoanalystsand has a very complcx however,there rvasstill a grcat deal of overlap between the definition, it might at first be thought of as a poor candi- patients and normafindicating that the dcficit is not suitdatc for a specific pathophysiology involving attentional able for making a differential diagnosis.The data shon'ed nel$'orks. Horr,,ever,we focuscd on the temperamentally a much smaller orienting deficit of thc type that had been based core svmptoms emotionality and difficulty in self- reported previously.Thesefindings suggestthat there is a regulation. We found thaLpaticnts were very high in nega- strong executivedeficit in chronic schizophrenia, asu,ould tive aff€ct and relatively low in effortful control (Rothbart, be anticipated by the Benes theory It remains to be deterAhadi, & Evans, 2000), and defined a temperamentally mincd r,"'hetherthis deficit is prior to the initial sl.mptoms matched control group of normal personswithout person- or rvhether it developswith Lhedisorder. ality disorder who wcre equivalent in these t$'o dimensions. Our studvwith the ANT found a delicit specificin the Chrcmosome 22q11.2deletion syndrome, This syndrome executiveattentiot network in borderline patients (Posner is a complexone that involveda number of abnormalitics ct al., 2002). Preliminary imaging results suggestedovcr- including facial and heart but also a mental retardation P R O B I NTGH EM E C H A N I S MOSFA T I E N T I O N that is due to deletion of a number of genes.It is known that thc children are at a high risk for the development of schizophrenia. Among the genes that arc deleted in this syndrorne is the COMT gene, which has bccn associated with a conflict task (Diamond et al., 2004) and with schizophrenia(Egan et al., 2001). In light of thesefindings it u,as to be expected that thc disorder would produce a largc exccutivedeficit (Simon et a1.,2005;Sobin et al., 2004). Sobin has suggestedin a firrther paper that' the dcficit in rcsolving conflict is associated'theability to l inhibit a blink following a cue that a loud noise would be presented shortly (pre-pulse inhibition). .The authors suggestthat the associationof thc high-levelattention and prcpulsc inhibition de6cit suggestsa pathway that includes b o t h t h e b c s a lg a n g l i aa n d t h e a n t e r i o rc i n g u l c r e . Many neurological and psychiatric disorders produce a difficulty in attention. Data to date suggcst that disorders havc specilic influenccs on attentional net$'orks.Houevcr, a number of disorders influence the same network (e.g., schizophrenia, borderline and Alzheimers dementia aff€ct executive attention) and the samc disorder can influence more than one network (e.g., schizophrenia may affect both lhe cxccutive and orienting network although perhaps at different stages of the disorder). These findings reduce the utility of attention as a means of classitying disorders, but they may be useful in suggestingmcthods of treatment at least of the attentional s)'rnptoms. 425 issue arose before there \\'as much discussion of specific brain mechanisms of attention. Many empirical studies were done to determine if attentional changcs showed up as alterations in the beta (decision) parameter of a sig, nal detection analysis olrvhether instead they involved changesin the di (sensory)parameter. AlLhoughmany elegantstudicswere conducted attcmpting to clarify this issue,there has becn no final resolution (although it seemslikcly that both paramctcrs can be varied by some experimental conditions). The earlv vcrsus late question can be resolvedinto thrcc somewhat intcrdependent issues. (1) Horv early in thc nervous system can atlention inlluence stimulus input? The results suggestthat it can be as early as Vl (Posner & Gilberf, 1999) under some conditions, but more oftcn attention influencc is in extrastriate visual arcas (Kastner et al., 1999).(2) How quickly after input can attention inlluence information processing?Again the cellular and physiological data indicate that it can be about as earll' as clear evidence of cortical processing can be obtaiaecl, although in many situations the influence is l1o1present un[il 80 100 millisecondsaftcr stimu]us onser(Mal1inez et al., 2001).Thc timing issueis of particular imporlancc becauseactivation ofa particular brain area may be eithcr along the input pathway,or could be due to teedbackfrom higher areas. (3) What does early selection mcan for the processing of information both selected and unselccted? Herc the answer is more complcx. It seemsto mean that certain aspects of complex scenes may be available fbr RESOLVINGENDURINGISSUESIN ATTENT:ON consciousreport whereasother aspectswill onlv be available if they succccdin producing reorienting. Unattended Modularity objects, however,rnay still be proccssedto fairly high lcvThere has been a great deal of discussion in the cognitive els and the processing itself may summon attention. Thc psychologv literature of the concept of modularit)'. These depth of cognitive processing of unattended objccts and discussionshavc often defined modularity in a way u,hich the possibility of attention to higher lelel codes suggests required a system to be unaffected by top down (attcn- that carly seleclion does not have thc cognitive consetional) inlluences in order to be modular. According to this quenceoriginally implied. Selectingone stimulus over othview only a \€ry fe\\' verlical sensory and motor systems ers does not mean that unselectcditcms will not producc could be modular (Fodor, 1983).Horveve6the evidence a reorienting of attention or still influence behavior that even primary sensory systems can be modulated by attcntion makcs it LrnlikclyLhatany higherJevel brain sysPriming lcms t'il1 mcct the criterion of modularity so defrned. Imaging data provides a rather dilferent perspectiveon Priming refers to the inJluenceofone event on the processmodularityl The material rcvicwcd in this chapter sug- ing ofsubsequcntcvcnts.Behavioralstudicssuggcsted that gcststhat even brain networks that rcllcct voluntary acti\L rcaction time could be improved to a target by the prcity such as executive attention may be modular in thc sentation of a stimulus (princ) that shares a part of thc sensethat very specificbrain areasperform computalions same pathway. Priming can occur in either of tlvo ways. reflecting thcir componcnt operations.This form of modu- In one way a stimulus activates a pathway automatically larity doesnot suggestthat thesemechanismswill operate and a second stimulus that shares the same path',vay is in the same u,ay irrespective of strategy or context. Ho\\'- improved in perlbrmance (Posner,1978).Theseeffccts can evcr, they do provide a starting place for linking cellular occur evenwhen the prime is prcsentedand maskedso that and genetic mechanismsto brain areasand then to cogni- subjects are not able to report its identit!'. Although there tive operations and behavior. has been a great dcal ofdispute about hotv to measlrreconscious processing,it appearsclear that priming can occur u,hcn subjectsare unable to rcporfevcn when stopped in Early and late seleqtion the middle of the trial.the natr,rreof the prime (Cheesman One of the oldest issues in the field of attention is how & Merikle, 1984).Most unconscious priming has bcen of early in processing can attention influence input. This sc[sory or semaltic codes, but under some conditions 426 (Dchaeneet al., 2003) even responsescan be primed without explicit knowledge of the nature of the prime. A sccond way that priming can occur is if a person attends to some feature that u'ill be sharcd by the target. For cxample, if people are taught that the word "animal" shoulJ bc inrerpretedcr a bod5 p n. lhr largetlfingef\\ill h . p r i m e d . f h e p r i m i n g i s k o m r h e ' u b j e c t sa t t - e n t i orno bodv part nor from aulomatic ilctivarionof fingcr by rhe prime arlimal. Data foom imaging studies of priming by input and by attention support this distinctionby showing very diffcrcnt cffccts on neural activity in the primed arca. lf priming occurs aul-omaticallv by input the target shows reduccd activationofthe primed cells.On thc other hand,attending to an area rvill enhancc neural activity and increase the effectof thc target(Corbettaet al., 1991). Thc ncrver imaging data shoq,sthe reality of thc disLinction bet\,"'eenautomatic priming and priming by attention. Horvever,it is not at all clear how the brain brings about similar chalgcs in performance sometimes by reducing and sometimes by increasing the activit), ofthe target. This puzzlc rcmains to be explained by future studies. POSNER R,U E D A&. K A N S K E lesion. Moreover, there has also been the argument that imaging does not prolide a good account of the computations that can predict the effect of damage (Utral, 2001). Herewe scc that the imaging results prolidc clcar cvidence of the importance of areas of the parietal lobe in shifts of attention and damageto theseareasrcgardlessofcause or orgalism interferes with oricnting. In addition, &f-cffons to better understand thc nature of the brain disordeithere have been efforts to adopt thcsc i d e a sr c l e t e dl o l h e p h y s i c abl a s i so l a n ( . n t i u n . t lO or rehabilitation. Some recent studies have tried to rehabilitate specificattentioual nctworks (Sohlberg et al., 2000; Sturm et al., 1997).Thesestudiessuggcstthat rehabilitationprocedures should focus on the parlicular attentional operations of the lesioned area, rvhile at the same time considering the contribution of thosc deficits to other attentional functions. In one study (Sturrn et a]', 1997),a computerizcd rchabilitation program was designedto try to cnhance specific attentional networks. The authors concluded from these fiDdings that vigilance and alertness arc the most fundamental functions in the hierarchy, and that selectiveattention and dividcd attention recruit these functions for thcir normal operation. Another study that utilized a practice Relation to neuropsychology oriented therapy (attention proccss therapy) with brainThe ability to image thc human brain has also provided injured patients showcd an orerall improvement in perfornerv perspectives for ncuropsychologists in their efforts mance (Sohlberget al., 2000). In some tasksthe group that to undcrstand, diagnose and treat insults to the human had relatively high vigilance scores showcd better cffccts brain that might occur as the result of strokc, tumot trau- of the therapy in agreementwith the Sturrn idea. matic injury; degenelative disease,or errors in dcvelopA third rehabilitation study tested the possible interacment (Fernandcz-Duque& Posner;2001). tion between vigilance and orienting by training patients As rre have argued, attention networks have anatomical to increase their self-alertncss, and cxploring $'hether and frrnctional indepenclence,but that the,valso interact the rehabilitation of sclf-alcrtness had an impact on in many practical situations. Damagc to a node of these paticnts'neglect(i.e.,orienting deficit) (Robertsonet al., netw,orks,inespective of thc sourcc, produces distincti!€ 1995). Exogenous alerlness was used as a basis for ncurops-vchologicaldeficits. This prirciple has been best training patients to self-alert. External rvarning signals established with respect to damage to thc parietal lobe. wcrc presented, and patients were instructed Lo gcncrStuclieshave sho',vnthat damage to palie|al neurons that atc a self-aletness signal in response to it. Exogcnous occur rnstroke, due to dcgcncral-ioninAlzheimeri disease, alertness, as produced by a loud noise, clepends on a blocking ofcholincrgic input, due to lesionsofnuclcus bas- thalamo-mcscncephalicpath and is relatively unimpaired salis, temporary damage liom transcranial magnetic stim- in right parietal patients. After the training proccdurc was ulation, direct injections of scopolamine, or closed head explaincd, the patient started the task and at variable interinjury all lead to diffrculties in using cues to process tar- vals the experimenter knocked on the tablc while at thc "Attend!" g e t . i n r h c r i s u a lf i r l d o p p o s i t et h e m a j o r i n s u l LR , e c e n t l y i sametime saying in a loud voice.At the nextstage normal personswho have one or two copics ofthe (4 allele in thc training, it was the patient who shouted "Attendl" of the apolipoprotcin E APOE4) gene which increasesthe each time the experimenter knocked on thc tablc. Latcr, risk of Alzheimer's disease,have also been shown to havc the paticnt would do both the knocking and the vocai increaseddifficulty in orienting attcntion and in adjusting command, first loudlr', then subvocally, and finally mcnthe spatial scale of attention,"howcvcr, thcy had no difE- tally. Patients were encouraged to try this self-alcrtness culty with maintaining thc alcrt state (Greenrvoodet al., method in their everydaylife. This rehabilitation training 2000). nol only improved patient'sself-alertness,but also rcduccd In oDe sensc the convergencebetween imaging, lesions the extent of their spatial neglect. and pharmacology in terms of cognitive effect is obvious. Taken together,these findings reveal benefits of systemIf computations of paric|al ncr.rronslcad to shifts of visual atically analyzing interactions and dissociations of the attentiori'damage to these neurons should producc dif6- attentional networks, instcad of treating attention as a culties. Yct therc has bec[ thc notion in ncuropsychology monolithic concept. They also demonstrate thal behavthat localization is not as imporlant as the cause of the ioral therapy can be successful in improving vigilancc P R O B I N GT H E M E C H A N I S M S OFATTENTION skills. 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