Posterior Parietal Cortex

Consensus across hundreds of published studies indicates that the same cortical regions are involved in many forms of cognitive control. Using functional magnetic resonance imaging (fMRI), we found that these coactive regions form a functionally connected cognitive control network (CCN). Network status was identified by convergent methods, including: high inter-regional correlations during rest and task performance, consistently higher correlations within the CCN than the rest of cortex, co-activation in a visual search task, and mutual sensitivity to decision difficulty. Regions within the CCN include anterior cingulate cortex/pre-supplementary motor area (ACC/pSMA), dorsolateral prefrontal cortex (DLPFC), inferior frontal junction (IFJ), anterior insular cortex (AIC), dorsal pre-motor cortex (dPMC), and posterior parietal cortex (PPC). We used a novel visual line search task which included periods when the probe stimuli were occluded but subjects had to maintain and update working...

The visual and auditory systems often concur to create a unified perceptual experience and to determine the localization of objects in the external world. Co-occurring auditory and visual stimuli in spatial coincidence are known to enhance performance of auditory localization due to the integration of stimuli from different sensory channels (i.e. multisensory integration). However, auditory localization of audiovisual stimuli presented at spatial disparity might also induce a mislocalization of the sound towards the visual stimulus (i.e. ventriloquism effect). Using repetitive transcranial magnetic stimulation we tested the role of right temporoparietal (rTPC), right occipital (rOC) and right posterior parietal (rPPC) cortex in an auditory localization task in which indices of ventriloquism and multisensory integration were computed. We found that suppression of rTPC excitability by means of continuous theta-burst stimulation (cTBS) reduced multisensory integration. No similar effec...

Crossmodal binding usually relies on bottom-up stimulus characteristics such as spatial and temporal correspondence. However, in case of ambiguity the brain has to decide whether to combine or segregate sensory inputs. We hypothesise that widespread, subtle forms of synesthesia provide crossmodal mapping patterns which underlie and influence multisensory perception. Our aim was to investigate if such a mechanism plays a role in the case of pitch-size stimulus combinations. Using a combination of psychophysics and ERPs, we could show that despite violations of spatial correspondence, the brain specifically integrates certain stimulus combinations which are congruent with respect to our hypothesis of pitch-size synesthesia, thereby impairing performance on an auditory spatial localisation task (Ventriloquist effect). Subsequently, we perturbed this process by functionally disrupting a brain area known for its role in multisensory processes, the right intraparietal sulcus, and observed how the Ventriloquist effect was abolished, thereby increasing behavioural performance. Correlating behavioural, TMS and ERP results, we could retrace the origin of the synesthestic pitch-size mappings to a right intraparietal involvement around 250ms. The results of this combined psychophysics, TMS and ERP study provide evidence for shifting the current viewpoint on synesthesia more towards synesthesia being at the extremity of a spectrum of normal, adaptive perceptual processes, entailing close interplay between the different sensory systems. Our results support this spectrum view of synesthesia by demonstrating that its neural basis crucially depends on normal multisensory processes.

Automatic mimicry is based on the tight linkage between motor and perception action representations in which internal models play a key role. Based on the anatomical connection, we hypothesized that the direct effective connectivity from the posterior superior temporal sulcus (pSTS) to the ventral premotor area (PMv) formed an inverse internal model, converting visual representation into a motor plan, and that reverse connectivity formed a forward internal model, converting the motor plan into a sensory outcome of action. To test this hypothesis, we employed dynamic causal-modeling analysis with functional magnetic-resonance imaging (fMRI). Twenty-four normal participants underwent a change-detection task involving two visually-presented balls that were either manually rotated by the investigator's right hand (“Hand”) or automatically rotated. The effective connectivity from the pSTS to the PMv was enhanced by hand observation and suppressed by execution, corresponding to the inverse model. Opposite effects were observed from the PMv to the pSTS, suggesting the forward model. Additionally, both execution and hand observation commonly enhanced the effective connectivity from the pSTS to the inferior parietal lobule (IPL), the IPL to the primary sensorimotor cortex (S/M1), the PMv to the IPL, and the PMv to the S/M1. Representation of the hand action therefore was implemented in the motor system including the S/M1. During hand observation, effective connectivity toward the pSTS was suppressed whereas that toward the PMv and S/M1 was enhanced. Thus, the action-representation network acted as a dynamic feedback-control system during action observation.

The nature of the neural system that directs our attention toward selective items in the extrapersonal world is a longstanding and interesting puzzle. The ability to image the human brain at work non-invasively using positron-emission tomography or functional magnetic resonance has provided the means to investigate this issue. In this article, I review the contributions of brain imaging toward the characterization of attentional control in the human brain. The majority of experiments to date have investigated visual spatial orienting. A consistent pattern of brain areas has been revealed, comprising most notably the posterior parietal cortex around the intraparietal sulcus and frontal regions including the frontal eye fields. The brain areas implicated in the control of visual spatial attention were noted to resemble those involved in the control of eye movements, and direct experimental comparisons supported a tight link between the two systems. The findings suggested a sensible view of the attentional 'homunculus' as a distributed neural system related to the control of eye movements. Eye movements form perhaps the most basic orienting response, and can be shifted rapidly and efficiently based on multiple frames of reference. Some attention experiments using objects and features instead of spatial locations as the target of selection also obtained similar patterns of parietal-frontal activations, rendering further support to this view of the attentional control system. Some recent experiments, however, have cautioned against a premature conclusion regarding the ubiquity of the attentional control system revealed by studies of visual spatial attention. Different parietal and frontal regions become engaged when attention is shifted along non-spatial dimensions, such as when attention is directed toward a particular motor act or toward a specific point in time. In these cases, the neural system resembles those involved in the control of limb movements. The attentional homunculus thus begins to dissolve. The alternative view suggested is that attentional control may be a property of specialized parietal-frontal systems that transform perception into action. Future studies will be needed to validate this view of attention, or to provide a more mature understanding of its true nature.

Synchrony among the senses lies at the heart of our possession of a unified conscious perception of the world. However, due to discrepancies in physical and neural information processing from different senses, the brain accommodates a limited range of temporal asynchronies between sensory inputs, i.e. the multisensory temporal binding window (TBW). Using non-invasive brain stimulation, we sought to modulate the audio-visual TBW and to identify cortical areas implicated in the conscious perception of multisensory synchrony. Participants performed a simultaneity judgment task while experiencing anodal (Experiment 1) or cathodal (Experiment 2) transcranial direct current stimulation (tDCS) over parietal and frontal regions. The results demonstrate that stimulating the right posterior parietal cortex significantly reduces the audio-visual TBW by approximately 30%, thereby causally linking this region to the plasticity of the TBW. This highlights a potential interventional technique for ...

We recorded neuronal responses to optic flow stimuli in the ventral intraparietal area (VIP) of two awake macaque monkeys. According to previous studies on optic flow responses in monkey extrastriate cortex we used different stimulus classes: frontoparallel motion, radial stimuli (expansion and contraction) and rotational stimuli (clockwise and counter-clockwise). Seventy- five percent of the cells showed statistically significant responses to

We placed injections of 3--5 distinguishable tracers in different dorsolateral locations in the visual cortex of four macaque monkeys to help define the extent of the dorsolateral visual complex (DL) commonly known as area V4. Injections well within DL/V4 region labeled neurons in V2, V3, MT, IT, and sometimes V1. In contrast, injections in caudal area 7a dorsal to current