Reticular Formation

This review considers some important landmarks in animal evolution, asking to what extent specialized action selection mechanisms play a role in the functional architecture of different nervous system plans, and looking for ‘forced moves’ or ‘good tricks’ (Dennett, 1995) that could possibly transfer to the design of robot control systems. A key conclusion is that while cnidarians (e.g. jellyfish) appear to have discovered some good tricks for the design of behavior-based control systems—largely lacking specialized selection mechanisms; the emergence of bilaterians may have forced the evolution of a central ganglion, or ‘archaic brain’, whose main function is to resolve conflicts between peripheral systems. Whilst vertebrates have many interesting selection substrates it is likely that here too, the evolution of centralized structures such as the medial reticular formation and the basal ganglia may have been a forced move due to the need to limit connection costs as brains increased in size.

This document collects a number of blog posts on the theme of behavioral mode. In this form the idea originates with Warren McCulloch, one of the grand old men of neuroscience and cybernetics. This conception would also give basic credence to the psychoanalytic conception of organ modes—oral, anal, and genital—though, ironically, McCulloch had little use for Freud—he entitled one of his papers “The Past of a Delusion” as an allusion to Freud’s The Future of an Illusion.

McCulloch’s idea is simple: The most basic decision any vertebrate can make is to commit to some mode of behavior—such as exploring, eating, courting, fighting, playing, etc. Any more specific direction is elaborated from within one of these modes. What gives MuCulloch’s idea its force is his argument (and accompanying model) that modal commitment was mediated, not by the most sophisticated and evolutionarily advanced brain tissue, but by the most elementary and evolutionarily old brain tissue. This tissue, known as the reticular formation or the reticular activating system, is at the core of the brainstem. In effect, it has veto power over the cerebral cortex, but also, the power to activate the cortex.

The seven posts in this document explore the implications of McCulloch’s conception of behavioral mode. In particular, these seven posts explore the implications of mode for our understanding of art and our construction of the self. They also lay the foundations for a pluralist view of the world.

Several areas in the brainstem and forebrain are important for the modulation and expression of the sleep/wake cycle. Even if the first observations of biochemical events in relation to sleep were made only 40 years ago, it is now well established that several neurotransmitters, neuropeptides, and neurohormones are involved in the modulation of the sleep/wake cycle.Serotonin has been known for many years to play a role in the modulation of sleep, however, it is still very controversial how and where serotonin may operate this modulation. Early studies suggested that serotonin is necessary to obtain and maintain behavioral sleep (permissive role on sleep).However, more recent microdialysis experiments provide evidence that the level of serotonin during W is higher in most cortical and subcortical areas receiving serotonergic projections. In this view the level of extracellular serotonin would be consistent with the pattern of discharge of the DRN serotonergic neurons which show the highest firing rate during W, followed by a decrease in slow wave sleep and by virtual electrical silence during REM sleep.This suggests that during waking serotonin may complement the action of noradrenaline and acetylcholine in promoting cortical responsiveness and participate to the inhibition of REM-sleep effector neurons in the brainstem (inhibitory role on REM sleep).The apparent inconsistency between an inhibitory and a facilitatory role played by serotonin on sleep has at least two possible explanations. On the one hand serotonergic modulation on the sleep/wake cycle takes place through a multitude of post-synaptic receptors which mediate different or even opposite responses; on the other hand the achievement of a behavioral state depends on the complex interaction between the serotonergic and other neurotransmitter systems.The main aim of this commentary is to review the role of brain serotonin in relation to the sleep/wake cycle. In particular we highlight the importance of microdialysis for on-line monitoring of the level of serotonin in different areas of the brain across the sleep/wake cycle.

This review article synthesizes studies ofartificial intelligence (AI) andbrain theory (BT). In the control ofmovement, AI offers insight into overallplanning of behavior; while control theory enables BT to modelfeedback andfeedforward adjustments by the spinal cord, brainstem, and cerebellum. We stressaction-oriented perception—analyzing perception in terms of preparation for interaction with the world, and offer a new concept of aschema as the

Despite in vivo studies suggesting an important function for nitric oxide (NO) in the spinal cord in the transmission of pain signals, sympathetic nerve activity and presumably other spinal functions, changes of neuronal NO synthase (nNOS)-containing neurons with aging in the spinal cord has not been investigated. In the present study, we demonstrated for the first time that the number of nNOS-immunoreactive neurons was significantly decreased in the central autonomic nucleus and the superficial dorsal horn of spinal cord in aged rats. Morphologically, the number and length of dendritic branches also seemed to be decreased. Combined with our previous studies, age-related decreases in the number of nNOS-immunoreactive neurons in the central autonomic nucleus and the superficial dorsal horn might be associated with the abnormality of micturition function or pain perception encountered in the elderly. However, the mechanisms underlying the decreased immunoreactivity for nNOS, and the functional implications require elucidation.

To examine the function of descending brain stem pathways in the control of locomotion, we have characterized the discharge patterns of identified vestibulo- and reticulospinal neurons (VSNs and RSNs, respectively) recorded from the lateral vestibular nucleus (LVN) and the medullary reticular formation (MRF), during treadmill walking. Data during locomotion were obtained for 44 VSNs and for 63 RSNs. The discharge frequency of most VSNs (42/44) was phasically modulated in phase with the locomotor rhythm and the averaged peak discharge frequency ranged from 41 to 165 Hz (mean = 92.8 Hz). We identified three classes of VSNs based on their discharge pattern. Type A, or double peak, VSNs (20/44 neurons, 46%) showed two peaks and two troughs of activity in each step cycle. One of the peaks was time-locked to the activity of extensor muscles in the ipsilateral hindlimb while the other occurred anti-phase to this period of activity. Type B, or single pause, neurons (13/44 neurons, 30%) were...

Nomifensine infusion in a pain facilitatory brain area raises local noradrenaline levels.Nomifensine infusion in a pain facilitatory brain area enhances pain behaviors.Nociceptive stimulation triggers the release of noradrenaline in a pain facilitatory brain area.Gene-mediated reduction of noradrenaline in a pain facilitatory area induces analgesia.Inhibiting noradrenaline recapture may enhance pain facilitation from the brain.Antidepressants that inhibit the recapture of noradrenaline have variable effects in chronic pain which may be related to the complex role of noradrenaline in pain modulation. Whereas at the spinal cord noradrenaline blocks nociceptive transmission, both antinociception and pronociception were reported after noradrenaline release in the brain. To study the role of noradrenaline in pain modulatory areas of the brain, we elected the dorsal reticular nucleus (DRt), a key pain facilitatory area located at the medulla oblongata. Three studies were performed. First, we show that the infusion in the DRt of nomifensine, which increases local extracellular levels of noradrenaline as shown by in vivo microdialysis, also enhances pain behavioral responses during both phases of the formalin test, a classic inflammatory pain model. Then, we demonstrate that the formalin test triggers the release of noradrenaline in the DRt in a biphasic pattern that matches the two phases of the test. Finally, we show that reducing noradrenaline release into the DRt, using an HSV-1 vector which decreases the expression of tyrosine hydroxylase in noradrenergic DRt-projecting neurons, attenuates pain behavioral responses in both phases of the formalin test. The increased noradrenaline levels induced by the infusion of nomifensine at the DRt, along with the hyperalgesic effects of noradrenaline released at the DRt upon noxious stimulation, indicates that noradrenaline may enhance pain facilitation from the brain. It is important to evaluate if antidepressants that inhibit noradrenaline recapture enhance pain facilitation from the brain herein attenuating their analgesic effects.

This mini-review considers certain factors related to the developmental decrease in rapid eye movement (REM) sleep, which occurs in favor of additional waking time, and its relationship to developmental factors that may influence its potential role in brain development. Specifically, we discuss some of the theories proposed for the occurrence of REM sleep and agree with the classic notion that REM sleep is, at the least, a mechanism that may play a role in the maturation of thalamocortical pathways. The developmental decrease in REM sleep occurs gradually from birth until close to puberty in the human, and in other mammals it is brief and coincides with eye and ear opening and the beginning of massive exogenous activation. Therefore, the purported role for REM sleep may change to involve a number of other functions with age. We describe recent findings showing that morphologic and physiologic properties as well as cholinergic, gamma amino-butyric acid, kainic acid, n-methyl-d-aspart...

The purpose of the present experiments was to test the hypothesis that the metrics of saccades caused by the activation of distinct collicular sites depend on the strength of their projections onto the burst generators. This study of morphofunctional correlations was limited to the horizontal components of saccades. We evoked saccades by stimulation of the deeper layers of the superior colliculus (SC) in alert, head-fixed cats. We used standard stimulus trains of 350 msec duration, 200 Hz pulse rate, and intensity set at two times saccade threshold in all experiments. Evoked saccades were analyzed quantitatively to determine the amplitude of the horizontal component of their "characteristic vectors". This parameter is independent of eye position and was used as the physiological, saccade-related metric of the stimulation sites. Anatomical connections arising from these sites were visualized after anterograde transport of biocytin injected through a micropipette adjoining t...

Following injury and inflammation, pain to light stroking (dynamic mechanical allodynia) might develop at the damaged site (primary area) or in adjacent normal tissue (secondary area). Using fMRI we mapped changes in the spinal trigeminal nucleus (spV), and supraspinal brainstem nuclei following heat/capsaicin-induced primary and secondary dynamic mechanical allodynia in the human trigeminal system. The role of these structures in dynamic mechanical allodynia has not been clarified yet in humans. During the control session we applied the same mechanical stimuli to the same untreated trigeminal area. Primary and secondary mechanical allodynia showed equal levels of perceived pain intensity, and compared to control mechanical stimulation exhibited similar responses in the ipsilateral spV and contralateral ventrolateral periaqueductal gray (vlPAG). Activity in the spV was significantly higher during both conditions versus the control mechanical stimulation, indicating that central sens...

The accessory optic system (AOS) is formed by a series of terminal nuclei receiving direct visual information from the retina via one or more accessory optic tracts. In addition to the retinal input, derived from ganglion cells that characteristically have large receptive fields, are direction-selective, and have a preference for slow moving stimuli, there are now well-characterized afferent connections with a key pretectal nucleus (nucleus of the optic tract) and the ventral lateral geniculate nucleus. The efferent connections of the AOS are robust, targeting brainstem and other structures in support of visual-oculomotor events such as optokinetic nystagmus and visual-vestibular interaction. This chapter reviews the newer experimental findings while including older data concerning the structural and functional organization of the AOS. We then consider the ontogeny and phylogeny of the AOS and include a discussion of similarities and differences in the anatomical organization of the...

 Microiontophoretic studies of thalamic neurons suggests that nitric oxide (NO) plays an important role in mediating somatosensory transmission. The thalamus contains few nitric oxide synthase (NOS)-immunoreactive neurons; thus, the major source of thalamic NO is presumably from NOS-positive axons of extrathalamic origin. The cells of origin of these putative NOS-containing pathways to the ventrobasal thalamus were investigated in rats by combining retrograde tracing with immunocytochemistry for NOS. The location and morphology of double-labeled neurons was compared with that of single-labeled neurons. The most significant sources of NOS-containing afferents to the thalamus were found to be the pedunculopontine (PPN) and laterodorsal tegmental (LDT) nuclei. NOS-immunoreactive neurons in these cholinergic nuclei project bilaterally to the thalamus, most strongly ipsilaterally. The thalamus appears to be a major target of PPN, since even selective thalamic injections result in retrograde labeling of at least one third of its NOS-immunoreactive neurons. A significant number of NOS-negative neurons in both the PPN and LDT also project to the thalamus. Minor sources of NOS-containing thalamic afferents include the lateral hypothalamus, the dorsal, median and pontine raphe nuclei, the parabrachial nuclei, and the pontomedullary reticular formation. In all these structures, NOS-negative thalamopetal neurons greatly outnumber the NOS-positive ones. Ascending sensory pathways to the thalamus, including those from the sensory trigeminal nuclei, the dorsal column nuclei, and the spinal cord, as well as the auditory and vestibular centers, arise exclusively from NOS-negative neurons. The major NOS-positive projections are implicated in affective and alerting systems, supporting that NO may act to modulate attentiveness in thalamic relay nuclei.