CiteULike: memphisphil's library [265 articles]

Right TPJ Deactivation during Visual Search: Functional Significance and Support for a Filter Hypothesis.

Gordon L Shulman — 2007-02-07T19:57:54-00:00

Cereb Cortex (30 January 2007)

Behavioral performance depends on attending to important objects in the environment rather than irrelevant objects. Regions in the right temporal-parietal junction (TPJ) are thought to be involved in redirecting attention to new objects that are behaviorally relevant. When subjects monitor a stream of distracter objects for a target, TPJ deactivates until the target is detected. We have proposed that the deactivation reflects the filtering of irrelevant inputs from TPJ, preventing unimportant objects from being attended. This hypothesis predicts that the mean deactivation to distracters should be larger when the subsequent target is detected than missed, reflecting more efficient filtering. An analysis of the blood oxygenation level-dependent (BOLD) task-evoked signals from 20 subjects during 2 monitoring tasks confirmed this prediction for regions in right supramarginal gyrus (SMG). Because the deactivation preceded the target, this mean BOLD-detection relationship did not reflect feedback from target detection or postdetection processes. The SMG regions showing this relationship overlapped or neighbored some regions associated with a "default" mode of brain function, suggesting the functional significance of deactivations in some default regions during task performance.

Working memory as an emergent property of the mind and brain.

BR Postle — 2007-05-03T20:38:20-00:00

Neuroscience, Vol. 139, No. 1. (28 April 2006), pp. 23-38.

Cognitive neuroscience research on working memory has been largely motivated by a standard model that arose from the melding of psychological theory with neuroscience data. Among the tenets of this standard model are that working memory functions arise from the operation of specialized systems that act as buffers for the storage and manipulation of information, and that frontal cortex (particularly prefrontal cortex) is a critical neural substrate for these specialized systems. However, the standard model has been a victim of its own success, and can no longer accommodate many of the empirical findings of studies that it has motivated. An alternative is proposed: Working memory functions arise through the coordinated recruitment, via attention, of brain systems that have evolved to accomplish sensory-, representation-, and action-related functions. Evidence from behavioral, neuropsychological, electrophysiological, and neuroimaging studies, from monkeys and humans, is considered, as is the question of how to interpret delay-period activity in the prefrontal cortex.

Computational correlates of consciousness.

A Cleeremans — 2007-05-03T20:34:43-00:00

Prog Brain Res, Vol. 150 (2005), pp. 81-98.

Over the past few years numerous proposals have appeared that attempt to characterize consciousness in terms of what could be called its computational correlates: Principles of information processing with which to characterize the differences between conscious and unconscious processing. Proposed computational correlates include architectural specialization (such as the involvement of specific regions of the brain in conscious processing), properties of representations (such as their stability in time or their strength), and properties of specific processes (such as resonance, synchrony, interactivity, or information integration). In exactly the same way as one can engage in a search for the neural correlates of consciousness, one can thus search for the computational correlates of consciousness. The most direct way of doing is to contrast models of conscious versus unconscious information processing. In this paper, I review these developments and illustrate how computational modeling of specific cognitive processes can be useful in exploring and in formulating putative computational principles through which to capture the differences between conscious and unconscious cognition. What can be gained from such approaches to the problem of consciousness is an understanding of the function it plays in information processing and of the mechanisms that subtend it. Here, I suggest that the central function of consciousness is to make it possible for cognitive agents to exert flexible, adaptive control over behavior. From this perspective, consciousness is best characterized as involving (1) a graded continuum defined over quality of representation, such that availability to consciousness and to cognitive control correlates with properties of representation, and (2) the implication of systems of meta-representations.

How many kinds of consciousness?

DM Rosenthal — 2007-05-03T20:34:00-00:00

Conscious Cogn, Vol. 11, No. 4. (December 2002), pp. 653-665.

Ned Block's influential distinction between phenomenal and access consciousness has become a staple of current discussions of consciousness. It is not often noted, however, that his distinction tacitly embodies unargued theoretical assumptions that favor some theoretical treatments at the expense of others. This is equally so for his less widely discussed distinction between phenomenal consciousness and what he calls reflexive consciousness. I argue that the distinction between phenomenal and access consciousness, as Block draws it, is untenable. Though mental states that have qualitative character plainly differ from those with no mental qualities, a mental state's being conscious is the same property for both kinds of mental state. For one thing, as Block describes access consciousness, that notion does not pick out any property that we intuitively count as a mental state's being conscious. But the deeper problem is that Block's notion of phenomenal consciousness, or phenomenality, is ambiguous as between two very different mental properties. The failure to distinguish these results in the begging of important theoretical questions. Once the two kinds of phenomenality have been distinguished, the way is clear to explain qualitative consciousness by appeal to a model such as the higher-order-thought hypothesis.

Conscious intention and motor cognition

Patrick Haggard — 2005-05-30T13:27:13-00:00

Trends in Cognitive Sciences, Vol. 9, No. 6. (June 2005), pp. 290-295.

The subjective experience of conscious intention is a key component of our mental life. Philosophers studying 'conscious free will' have discussed whether conscious intentions could cause actions, but modern neuroscience rejects this idea of mind-body causation. Instead, recent findings suggest that the conscious experience of intending to act arises from preparation for action in frontal and parietal brain areas. Intentional actions also involve a strong sense of agency, a sense of controlling events in the external world. Both intention and agency result from the brain processes for predictive motor control, not merely from retrospective inference.

Global workspace theory of consciousness: toward a cognitive neuroscience of human experience.

BJ Baars — 2007-05-03T20:33:41-00:00

Prog Brain Res, Vol. 150 (2005), pp. 45-53.

Global workspace (GW) theory emerged from the cognitive architecture tradition in cognitive science. Newell and co-workers were the first to show the utility of a GW or "blackboard" architecture in a distributed set of knowledge sources, which could cooperatively solve problems that no single constituent could solve alone. The empirical connection with conscious cognition was made by Baars (1988, 2002). GW theory generates explicit predictions for conscious aspects of perception, emotion, motivation, learning, working memory, voluntary control, and self systems in the brain. It has similarities to biological theories such as Neural Darwinism and dynamical theories of brain functioning. Functional brain imaging now shows that conscious cognition is distinctively associated with wide spread of cortical activity, notably toward frontoparietal and medial temporal regions. Unconscious comparison conditions tend to activate only local regions, such as visual projection areas. Frontoparietal hypometabolism is also implicated in unconscious states, including deep sleep, coma, vegetative states, epileptic loss of consciousness, and general anesthesia. These findings are consistent with the GW hypothesis, which is now favored by a number of scientists and philosophers.

A connectionist theory of phenomenal experience.

G O'Brien — 2007-05-03T20:33:26-00:00

Behav Brain Sci, Vol. 22, No. 1. (February 1999)

When cognitive scientists apply computational theory to the problem of phenomenal consciousness, as many have been doing recently, there are two fundamentally distinct approaches available. Consciousness is to be explained either in terms of the nature of the representational vehicles the brain deploys or in terms of the computational processes defined over these vehicles. We call versions of these two approaches vehicle and process theories of consciousness, respectively. However, although there may be space for vehicle theories of consciousness in cognitive science, they are relatively rare. This is because of the influence exerted, on the one hand, by a large body of research that purports to show that the explicit representation of information in the brain and conscious experience are dissociable, and on the other, by the classical computational theory of mind--the theory that takes human cognition to be a species of symbol manipulation. Two recent developments in cognitive science combine to suggest that a reappraisal of this situation is in order. First, a number of theorists have recently been highly critical of the experimental methodologies used in the dissociation studies--so critical, in fact, that it is no longer reasonable to assume that the dissociability of conscious experience and explicit representation has been adequately demonstrated. Second, classicism, as a theory of human cognition, is no longer as dominant in cognitive science as it once was. It now has a lively competitor in the form of connectionism; and connectionism, unlike classicism, does have the computational resources to support a robust vehicle theory of consciousness. In this target article we develop and defend this connectionist vehicle theory of consciousness. It takes the form of the following simple empirical hypothesis: phenomenal experience consists of the explicit representation of information in neurally realized parallel distributed processing (PDP) networks. This hypothesis leads us to reassess some common wisdom about consciousness, but, we argue, in fruitful and ultimately plausible ways.

Two neural correlates of consciousness

Ned Block — 2005-05-17T13:49:34-00:00

Trends in Cognitive Sciences, Vol. 9, No. 2. (February 2005), pp. 46-52.

Neuroscientists continue to search for 'the' neural correlate of consciousness (NCC). In this article, I argue that a framework in which there are at least two distinct NCCs is increasingly making more sense of empirical results than one in which there is a single NCC. I outline the distinction between phenomenal NCC and access NCC, and show how they can be distinguished by experimental approaches, in particular signal-detection theory approaches. Recent findings in cognitive neuroscience provide an empirical case for two different NCCs.

A neuronal network model linking subjective reports and objective physiological data during conscious perception.

S Dehaene — 2006-04-13T08:02:21-00:00

Proc Natl Acad Sci U S A, Vol. 100, No. 14. (8 July 2003), pp. 8520-8525.

The subjective experience of perceiving visual stimuli is accompanied by objective neuronal activity patterns such as sustained activity in primary visual area (V1), amplification of perceptual processing, correlation across distant regions, joint parietal, frontal, and cingulate activation, gamma-band oscillations, and P300 waveform. We describe a neuronal network model that aims at explaining how those physiological parameters may cohere with conscious reports. The model proposes that the step of conscious perception, referred to as access awareness, is related to the entry of processed visual stimuli into a global brain state that links distant areas including the prefrontal cortex through reciprocal connections, and thus makes perceptual information reportable by multiple means. We use the model to simulate a classical psychological paradigm: the attentional blink. In addition to reproducing the main objective and subjective features of this paradigm, the model predicts an unique property of nonlinear transition from nonconscious processing to subjective perception. This all-or-none dynamics of conscious perception was verified behaviorally in human subjects.

Conscious, preconscious, and subliminal processing: a testable taxonomy.

S Dehaene — 2007-05-03T20:18:34-00:00

Trends Cogn Sci, Vol. 10, No. 5. (May 2006), pp. 204-211.

Of the many brain events evoked by a visual stimulus, which are specifically associated with conscious perception, and which merely reflect non-conscious processing? Several recent neuroimaging studies have contrasted conscious and non-conscious visual processing, but their results appear inconsistent. Some support a correlation of conscious perception with early occipital events, others with late parieto-frontal activity. Here we attempt to make sense of these dissenting results. On the basis of the global neuronal workspace hypothesis, we propose a taxonomy that distinguishes between vigilance and access to conscious report, as well as between subliminal, preconscious and conscious processing. We suggest that these distinctions map onto different neural mechanisms, and that conscious perception is systematically associated with surges of parieto-frontal activity causing top-down amplification.

A neuronal model of a global workspace in effortful cognitive tasks.

S Dehaene — 2007-05-03T20:17:43-00:00

Proc Natl Acad Sci U S A, Vol. 95, No. 24. (24 November 1998), pp. 14529-14534.

A minimal hypothesis is proposed concerning the brain processes underlying effortful tasks. It distinguishes two main computational spaces: a unique global workspace composed of distributed and heavily interconnected neurons with long-range axons, and a set of specialized and modular perceptual, motor, memory, evaluative, and attentional processors. Workspace neurons are mobilized in effortful tasks for which the specialized processors do not suffice. They selectively mobilize or suppress, through descending connections, the contribution of specific processor neurons. In the course of task performance, workspace neurons become spontaneously coactivated, forming discrete though variable spatio-temporal patterns subject to modulation by vigilance signals and to selection by reward signals. A computer simulation of the Stroop task shows workspace activation to increase during acquisition of a novel task, effortful execution, and after errors. We outline predictions for spatio-temporal activation patterns during brain imaging, particularly about the contribution of dorsolateral prefrontal cortex and anterior cingulate to the workspace.

Large-scale neural model for visual attention: integration of experimental single-cell and fMRI data.

S Corchs — 2007-05-03T20:15:19-00:00

Cereb Cortex, Vol. 12, No. 4. (April 2002), pp. 339-348.

A computational neuroscience framework is proposed to better understand the role and the neuronal correlate of spatial attention modulation in visual perception. The model consists of several interconnected modules that can be related to the different areas of the dorsal and ventral paths of the visual cortex. Competitive neural interactions are implemented at both microscopic and interareal levels, according to the biased competition hypothesis. This hypothesis has been experimentally confirmed in studies in humans using functional magnetic resonance imaging (fMRI) techniques and also in single-cell recording studies in monkeys. Within this neuro-dynamical approach, numerical simulations are carried out that describe both the fMRI and the electrophysiological data. The proposed model draws together data of different spatial and temporal resolution, as are the above-mentioned imaging and single-cell results.

Inattentional Blindness Versus Inattentional Amnesia for Fixated But Ignored Words

Geraint Rees — 2007-05-03T20:10:10-00:00

Science, Vol. 286, No. 5449. (24 December 1999), pp. 2504-2507.

10.1126/science.286.5449.2504

A report of the functional connectivity workshop, Dusseldorf 2002.

L Lee — 2007-05-03T20:06:33-00:00

Neuroimage, Vol. 19, No. 2 Pt 1. (June 2003), pp. 457-465.

This report provides a commentary on the issues presented and discussed at the recent "Functional Brain Connectivity" workshop, held in Dusseldorf, Germany. The workshop brought together researchers using different approaches to study connectivity in the brain, providing them with an opportunity to share conceptual, mathematical, and experimental ideas and to develop strategies and collaborations for future work on functional integration. The main themes that emerged included: (1) the importance of anatomical knowledge in understanding functional interactions the brain; (2) the need to establish common definitions for terms used across disciplines; (3) the need to develop a satisfactory framework for inferring causality from functional imaging and EEG/MEG data; (4) the importance of analytic tools that capture the dynamics of neural interactions; and (5) the role of experimental paradigms that exploit the functional imaging of perturbations to cortical interactions.

Automatic avoidance of obstacles is a dorsal stream function: evidence from optic ataxia.

I Schindler — 2007-04-14T00:58:27-00:00

Nat Neurosci, Vol. 7, No. 7. (July 2004), pp. 779-784.

When we reach out to pick something up, our arm is directed to the target by visuomotor networks in the cortical dorsal stream. However, our reach trajectories are influenced also by nontarget objects, which might be construed as potential obstacles. We tested two patients with bilateral dorsal-stream (parietal lesions, both of whom were impaired at pointing to visual stimuli (optic ataxia). We asked them to reach between two cylinders, which varied in location from trial to trial. We found that the patients' reaches remained invariant with changes in obstacle location. In a control task when they were asked to point midway between the two objects, however, their responses shifted in an orderly fashion. We conclude that the dorsal stream provides the visual guidance we automatically build into our movements to avoid potential obstacles, as well as that required to ensure arrival at the target.

Automatic obstacle avoidance and parietal cortex.

GW Humphreys — 2007-04-14T00:57:55-00:00

Nat Neurosci, Vol. 7, No. 7. (July 2004)

Parietal cortex mediates voluntary control of spatial and nonspatial auditory attention.

S Shomstein — 2007-04-14T00:57:07-00:00

J Neurosci, Vol. 26, No. 2. (11 January 2006), pp. 435-439.

The human posterior parietal cortex (PPC) is widely believed to subserve visually guided spatial behavior, including the control of visual attention, eye movements, and reaching. To explore the generality of this function, we measured human brain activity using functional magnetic resonance imaging during spatial and nonspatial shifts of auditory attention. Both spatial and nonspatial shifts of auditory attention evoked transient activity in the medial superior parietal cortex. These results reveal that the PPC is not exclusively devoted to visuospatial behavior; similar regions within a dorsomedial subcompartment provide a domain-independent reconfiguration signal for the control of spatial and nonspatial attention in both visual and nonvisual modalities.

Multimodal spatial representations in the human parietal cortex: evidence from functional imaging.

E Macaluso — 2007-04-14T00:56:29-00:00

Adv Neurol, Vol. 93 (2003), pp. 219-233.

Intermittent visuomotor processing in the human cerebellum, parietal cortex, and premotor cortex.

DE Vaillancourt — 2007-04-14T00:55:49-00:00

J Neurophysiol, Vol. 95, No. 2. (February 2006), pp. 922-931.

The cerebellum, parietal cortex, and premotor cortex are integral to visuomotor processing. The parameters of visual information that modulate their role in visuomotor control are less clear. From motor psychophysics, the relation between the frequency of visual feedback and force variability has been identified as nonlinear. Thus we hypothesized that visual feedback frequency will differentially modulate the neural activation in the cerebellum, parietal cortex, and premotor cortex related to visuomotor processing. We used functional magnetic resonance imaging at 3 Tesla to examine visually guided grip force control under frequent and infrequent visual feedback conditions. Control conditions with intermittent visual feedback alone and a control force condition without visual feedback were examined. As expected, force variability was reduced in the frequent compared with the infrequent condition. Three novel findings were identified. First, infrequent (0.4 Hz) visual feedback did not result in visuomotor activation in lateral cerebellum (lobule VI/Crus I), whereas frequent (25 Hz) intermittent visual feedback did. This is in contrast to the anterior intermediate cerebellum (lobule V/VI), which was consistently active across all force conditions compared with rest. Second, confirming previous observations, the parietal and premotor cortices were active during grip force with frequent visual feedback. The novel finding was that the parietal and premotor cortex were also active during grip force with infrequent visual feedback. Third, right inferior parietal lobule, dorsal premotor cortex, and ventral premotor cortex had greater activation in the frequent compared with the infrequent grip force condition. These findings demonstrate that the frequency of visual information reduces motor error and differentially modulates the neural activation related to visuomotor processing in the cerebellum, parietal cortex, and premotor cortex.

Virtual lesions of the anterior intraparietal area disrupt goal-dependent on-line adjustments of grasp

Eugene Tunik — 2005-03-28T21:54:56-00:00

Nature Neuroscience, Vol. 8, No. 4. (20 March 2005), pp. 505-511.

Cortical mechanisms of space-based and object-based attentional control.

S Yantis — 2007-03-28T18:17:36-00:00

Curr Opin Neurobiol, Vol. 13, No. 2. (April 2003), pp. 187-193.

Visual attention, the mechanism by which observers select relevant or important information from scenes, can be deployed to locations in space or to spatially invariant object representations. Studies have examined both the modulatory effects of attention on the strength of extrastriate cortical representations, and the control of attention by parietal and frontal cortical circuits. Subregions of parietal and frontal cortex are transiently active when attention is voluntarily shifted between spatial locations or object representations. This transient activity may reflect an abrupt shift in the attentional set of the observer, complementing sustained signals that are thought to maintain a given attentive state.

Concurrent TMS-fMRI and Psychophysics Reveal Frontal Influences on Human Retinotopic Visual Cortex

Christian Ruff — 2006-10-22T04:23:27-00:00

Current Biology, Vol. 16, No. 15. (8 August 2006), pp. 1479-1488.

SummaryBackgroundRegions in human frontal cortex may have modulatory top-down influences on retinotopic visual cortex, but to date neuroimaging methods have only been able to provide indirect evidence for such functional interactions between remote but interconnected brain regions. Here we combined transcranial magnetic stimulation (TMS) with concurrent functional magnetic resonance imaging (fMRI), plus psychophysics, to show that stimulation of the right human frontal eye-field (FEF) produced a characteristic topographic pattern of activity changes in retinotopic visual areas V1-V4, with functional consequences for visual perception.ResultsFEF TMS led to activity increases for retinotopic representations of the peripheral visual field, but to activity decreases for the central field, in areas V1-V4. These frontal influences on visual cortex occurred in a top-down manner, independently of visual input. TMS of a control site (vertex) did not elicit such visual modulations, and saccades, blinks, or pupil dilation could not account for our results. Finally, the effects of FEF TMS on activity in retinotopic visual cortex led to a behavioral prediction that we confirmed psychophysically by showing that TMS of the frontal site (again compared with vertex) enhanced perceived contrast for peripheral relative to central visual stimuli.ConclusionsOur results provide causal evidence that circuits originating in the human FEF can modulate activity in retinotopic visual cortex, in a manner that differentiates the central and peripheral visual field, with functional consequences for perception. More generally, our study illustrates how the new approach of concurrent TMS-fMRI can now reveal causal interactions between remote but interconnected areas of the human brain.

Visuomotor functions of the posterior parietal cortex.

SR Jackson — 2007-03-05T19:31:08-00:00

Neuropsychologia, Vol. 44, No. 13. (2006), pp. 2589-2593.

In this special issue of Neuropsychologia leading experts in the field discuss controversies and advances in the role of the posterior parietal cortex (PPC) in visuomotor control. The papers are wide-ranging in their scope, covering monkey physiology and anatomy, functional imaging in humans and monkeys as well as transcranial magnetic stimulation and lesion studies in humans. The collection provides an important overview of the current state-of the-art in this area of research, including discussions on homologies between monkey and human parietal regions, the role of co-ordinate transformations and intermediate representations from vision to action, and reviews of controversial hot topics in this field.

Parietal cortex and attention.

M Behrmann — 2005-11-17T19:52:47-00:00

Curr Opin Neurobiol, Vol. 14, No. 2. (April 2004), pp. 212-217.

The parietal lobe forms about 20% of the human cerebral cortex and is divided into two major regions, the somatosensory cortex and the posterior parietal cortex. Posterior parietal cortex, located at the junction of multiple sensory regions, projects to several cortical and subcortical areas and is engaged in a host of cognitive operations. One such operation is selective attention, the process where by the input is filtered and a subset of the information is selected for preferential processing. Recent neuroimaging and neuropsychological studies have provided a more fine-grained understanding of the relationship between brain and behavior in the domain of selective attention.

Single-pulse transcranial magnetic stimulation of parietal and prefrontal areas in a memory delay arm pointing task.

N Smyrnis — 2007-04-14T00:50:39-00:00

J Neurophysiol, Vol. 89, No. 6. (June 2003), pp. 3344-3350.

Fifteen healthy volunteers performed a memory-pointing task using their right arm while single-pulse transcranial magnetic stimulation (TMS) above motor threshold was applied over the posterior parietal or prefrontal cortex of the left or right hemisphere in four blocks of trials. The stimulation was randomly delivered at one of three time intervals during the 3-s delay period (early: 300 ms, intermediate: 1,500 ms, late: 2,700 ms). A separate block with no stimulation was used as control. Only early left parietal stimulation resulted in an increase in the variance of movement amplitude but not direction for all targets in two-dimensional space (both hemifields). The results point to the significance of the contralateral posterior parietal cortex early on during the memorization of the target for an upcoming movement. Taking into consideration the limitations of TMS and those imposed by the particular task, the lack of specific effects of prefrontal stimulation provides evidence that these areas might not be involved in the performance of simple memorized arm movements.

Interactions between ego- and allocentric neuronal representations of space.

S F W Neggers — 2006-03-06T09:10:06-00:00

Neuroimage (8 February 2006)

In the primate brain, visual spatial representations express distances of objects with regard to different references. In the parietal cortex, distances are thought to be represented with respect to the body (egocentric representation) and in superior temporal cortices with respect to other objects, independent of the observer (allocentric representation). However, these representations of space are interdependent, complicating such distinctions. Specifically, an object's position within a background frame strongly biases egocentric position location judgments. This bias, however, is absent for pointing movements towards that same object. More recent theories state that dorsal parietal spatial representations subserve visuomotor processing, whereas temporal lobe representations subserve memory and cognition. Therefore, it may be hypothesized that parietal egocentric representations, responsible for movement control, are not influenced by irrelevant allocentric cues, whereas ventral representations are. In an event-related functional magnetic resonance imaging study, subjects judged target bar locations relative to their body (egocentric task) or a background bar (allocentric task). Activity in the superior parietal lobule (SPL) was shown to increase during egocentric judgments, but not during allocentric judgments. The superior temporal gyrus (STG) shows a negative BOLD response during allocentric judgments and no activation during egocentric judgments. During egocentric judgments, the irrelevant background influenced activity in the posterior commissure and the medial temporal gyrus. SPL activity was unaffected by the irrelevant background during egocentric judgments. Sensitivity to spatial perceptual biases is apparently limited to occipito-temporal areas, subserving the observed biased cognitive reports of location, and is not found in parietal areas, subserving unbiased goal-directed actions.

Exploring the contributions of premotor and parietal cortex to spatial compatibility using image-guided TMS.

L Koski — 2007-04-14T00:49:19-00:00

Neuroimage, Vol. 24, No. 2. (15 January 2005), pp. 296-305.

Functional brain imaging studies have demonstrated increased activity in dorsal premotor and posterior parietal cortex when performing spatial stimulus-response compatibility tasks (SRC). We tested the specific role of these regions in stimulus-response mapping using single-pulse transcranial magnetic stimulation (TMS). Subjects were scanned using functional magnetic resonance imaging (fMRI) prior to the TMS session during performance of a task in which spatial compatibility was manipulated. For each subject, the area of increased signal within the regions of interest was registered onto their own high-resolution T1-weighted anatomic scan. TMS was applied to these areas for each subject using a frameless stereotaxic system. Task accuracy and reaction time (RT) were measured during blocks of compatible or incompatible trials and during blocks of real TMS or sham stimulation. On each trial, a single TMS pulse was delivered at 50, 100, 150, or 200 ms after the onset of the stimulus in the left or right visual field. TMS over the left premotor cortex produced various facilitatory effects, depending on the timing of the stimulation. At short intervals, TMS appeared to prime the left dorsal premotor cortex to select a right-hand response more quickly, regardless of stimulus-response compatibility. The strongest effect of stimulation, however, occurred at the 200-ms interval, when TMS facilitated left-hand responses during the incompatible condition. Facilitation of attention to the contralateral visual hemifield was observed during stimulation over the parietal locations. We conclude that the left premotor cortex is one of the cortical regions responsible for overriding automatic stimulus-response associations.

Role of the posterior parietal cortex in updating reaching movements to a visual target.

M Desmurget — 2007-04-14T00:43:22-00:00

Nat Neurosci, Vol. 2, No. 6. (June 1999), pp. 563-567.

The exact role of posterior parietal cortex (PPC) in visually directed reaching is unknown. We propose that, by building an internal representation of instantaneous hand location, PPC computes a dynamic motor error used by motor centers to correct the ongoing trajectory. With unseen right hands, five subjects pointed to visual targets that either remained stationary or moved during saccadic eye movements. Transcranial magnetic stimulation (TMS) was applied over the left PPC during target presentation. Stimulation disrupted path corrections that normally occur in response to target jumps, but had no effect on those directed at stationary targets. Furthermore, left-hand movement corrections were not blocked, ruling out visual or oculomotor effects of stimulation.

Attention systems and the organization of the human parietal cortex.

MF Rushworth — 2007-04-14T00:42:43-00:00

J Neurosci, Vol. 21, No. 14. (15 July 2001), pp. 5262-5271.

Event-related functional magnetic resonance imaging was used to compare activity in the human parietal cortex in two attention-switching paradigms. On each trial of the visual switching (VS) paradigm, subjects attended to one of two visual stimuli on the basis of either their color or shape. Trials were presented in blocks interleaved with cues instructing subjects to either continue attending to the currently relevant dimension or to switch to the other stimulus dimension. In the response switching (RS) paradigm, subjects made one of two manual responses to the single stimulus presented on each trial. The rules for stimulus-response mapping were reversed on different trials. Trials were presented in blocks interleaved with cues that instructed subjects to either switch stimulus-response mapping rules or to continue with the current rule. Brain activity at "switch" and "stay" events was compared. The results revealed distinct parietal areas concerned with visual attentional set shifts (VS) and visuomotor intentional set shifts (RS). In VS, activity was recorded in the lateral part of the intraparietal region. In RS, activity was recorded in the posterior medial intraparietal region and adjacent posterior superior and dorsomedial parietal cortex. The results also suggest that the basic functional organization of the intraparietal sulcus and surrounding regions is similar in both macaque and human species.

Control of visuotemporal attention by inferior parietal and superior temporal cortex.

K Shapiro — 2007-04-14T00:42:00-00:00

Curr Biol, Vol. 12, No. 15. (6 August 2002), pp. 1320-1325.

The human cortical visual system is organized into major pathways: a dorsal stream projecting to the superior parietal lobe (SPL), considered to be critical for visuospatial perception or on-line control of visually guided movements, and a ventral stream leading to the inferotemporal cortex, mediating object perception. Between these structures lies a large region, consisting of the inferior parietal lobe (IPL) and superior temporal gyrus (STG), the function of which is controversial. Lesions here can lead to spatial neglect, a condition associated with abnormal visuospatial perception as well as impaired visually guided movements, suggesting that the IPL+STG may have largely a "dorsal" role. Here, we use a nonspatial task to examine the deployment of visuotemporal attention in focal lesion patients, with or without spatial neglect. We show that, regardless of the presence of neglect, damage to the IPL+STG leads to a more prolonged deployment of visuotemporal attention compared to lesions of the SPL. Our findings suggest that the human IPL+STG makes an important contribution to nonspatial perception, and this is consistent with a role that is neither strictly "dorsal" nor "ventral". We propose instead that the IPL+STG has a top-down control role, contributing to the functions of both dorsal and ventral visual systems.

Right parietal cortex plays a critical role in change blindness.

DM Beck — 2007-04-14T00:41:22-00:00

Cereb Cortex, Vol. 16, No. 5. (May 2006), pp. 712-717.

There is increasing evidence from functional magnetic resonance imaging (fMRI) that visual awareness is not only associated with activity in ventral visual cortex but also with activity in the parietal cortex. However, due to the correlational nature of neuroimaging, it remains unclear whether this parietal activity plays a causal role in awareness. In the experiment presented here we disrupted activity in right or left parietal cortex by applying repetitive transcranial magnetic stimulation (rTMS) over these areas while subjects attempted to detect changes between two images separated by a brief interval (i.e. 1-shot change detection task). We found that rTMS applied over right parietal cortex but not left parietal cortex resulted in longer latencies to detect changes and a greater rate of change blindness compared with no TMS. These results suggest that the right parietal cortex plays a critical role in conscious change detection.

Parietal magnetic stimulation delays visuomotor mental rotation at increased processing demands.

S Bestmann — 2007-04-14T00:40:29-00:00

Neuroimage, Vol. 17, No. 3. (November 2002), pp. 1512-1520.

Visuomotor rotation (VMR) is a variant of the classic mental rotation paradigm. Subjects perform a center-out arm reaching movement, with the instruction to point clockwise or anticlockwise away from the direction of a reaction signal by a prespecified amount. Like classic mental rotation (MR) tasks, there is a linear relationship between reaction time (RT) and required angle of rotation (angular disparity). Although functional imaging studies have consistently demonstrated parietal activations centered around the intraparietal sulcus during MR tasks, the involvement of parietal cortex in VMR has not been investigated. The aim of the present experiments was to test in human subjects whether VMR also involves activity in parietal areas. We used short trains of transcranial magnetic stimulation (TMS) to produce a temporary "virtual lesion" of the posterior parietal cortex (PPC) around the intraparietal sulcus during the reaction period of a VMR task. Four pulses of 20-Hz rTMS were applied to the left PPC, right PPC, or vertex (control condition) 100 ms after the presentation of an instruction cue. Reaction times (RTs) were evenly prolonged by right or left parietal TMS compared with vertex stimulation, but only for large angles of rotation, and without affecting the spatial accuracy of the final response. A control experiment showed that parietal rTMS did not impair visual perception or the ability to judge the size of visual angles. The data thus provide evidence for bilateral involvement of the PPC in VMR that increases with processing demands.

Opposite biases in salience-based selection for the left and right posterior parietal cortex

Carmel Mevorach — 2006-05-26T21:58:12-00:00

Nature Neuroscience, Vol. 9, No. 6. (14 May 2006), pp. 740-742.

Modality-specific control of strategic spatial attention in parietal cortex.

CD Chambers — 2007-04-14T00:37:30-00:00

Neuron, Vol. 44, No. 6. (16 December 2004), pp. 925-930.

The neural basis of selective spatial attention presents a significant challenge to cognitive neuroscience. Recent neuroimaging studies have suggested that regions of the parietal and temporal cortex constitute a "supramodal" network that mediates goal-directed attention in multiple sensory modalities. Here we used transcranial magnetic stimulation (TMS) to determine which cortical subregions control strategic attention in vision and touch. Healthy observers undertook an orienting task in which a central arrow cue predicted the location of a subsequent visual or somatosensory target. To determine the attentional role of cortical subregions at different stages of processing, TMS was delivered to the right hemisphere during cue or target events. Results indicated a critical role of the inferior parietal cortex in strategic orienting to visual events, but not to somatosensory events. These findings are inconsistent with the existence of a supramodal attentional network and instead provide direct evidence for modality-specific attentional processing in parietal cortex.

Transcranial magnetic stimulation to right parietal cortex modifies the attentional blink

Adamc — 2006-12-11T22:24:10-00:00

Experimental Brain Research, Vol. V155, No. 1. (1 March 2004), pp. 24-29.

Cortico-cortical interactions in spatial attention: A combined ERP/TMS study.

G Fuggetta — 2007-04-14T00:32:58-00:00

J Neurophysiol, Vol. 95, No. 5. (May 2006), pp. 3277-3280.

To gain insight into the neural basis of visual attention, we combined transcranial magnetic stimulation (TMS) and event-related potentials (ERPs) during a visual search task. Single-pulse TMS over right posterior parietal cortex (rPPC) delayed response times to targets during conjunction search, and this behavioral effect had a direct ERP correlate. The early phase of the N2pc component that reflects the focusing of attention onto target locations in a search display was eliminated over the right hemisphere when TMS was applied there but was present when TMS was delivered to a control site (vertex). This finding demonstrates that rPPC TMS interferes with attentional selectivity in remote visual areas.

Topographic maps of visual spatial attention in human parietal cortex.

MA Silver — 2005-10-08T21:39:12-00:00

J Neurophysiol, Vol. 94, No. 2. (August 2005), pp. 1358-1371.

Functional magnetic resonance imaging (fMRI) was used to measure activity in human parietal cortex during performance of a visual detection task in which the focus of attention systematically traversed the visual field. Critically, the stimuli were identical on all trials (except for slight contrast changes in a fully randomized selection of the target locations) whereas only the cued location varied. Traveling waves of activity were observed in posterior parietal cortex consistent with shifts in covert attention in the absence of eye movements. The temporal phase of the fMRI signal in each voxel indicated the corresponding visual field location. Visualization of the distribution of temporal phases on a flattened representation of parietal cortex revealed at least two distinct topographically organized cortical areas within the intraparietal sulcus (IPS), each representing the contralateral visual field. Two cortical areas were proposed based on this topographic organization, which we refer to as IPS1 and IPS2 to indicate their locations within the IPS. This nomenclature is neutral with respect to possible homologies with well-established cortical areas in the monkey brain. The two proposed cortical areas exhibited relatively little response to passive visual stimulation in comparison with early visual areas. These results provide evidence for multiple topographic maps in human parietal cortex.

Action control in visual neglect.

E Coulthard — 2007-04-14T00:14:14-00:00

Neuropsychologia, Vol. 44, No. 13. (2006), pp. 2717-2733.

Patients with unilateral neglect show a variety of impairments when reaching towards objects in contralesional space. The basis of these deficits could be perceptual, motor or at one of the intermediate stages linking these processes. Here, we review studies of visually guided reaching in neglect and integrate these results with findings from normal human and monkey action control. We consider evidence which shows that neglect patients can be slow to initiate or execute reaches particularly to a contralesional target. We discuss the directional and spatial deficits that may interact to contribute to such reaching abnormalities and highlight the importance of effective target selection and on-line guidance, exploring the idea that deficits in these mechanisms underlie increased susceptibility to ipsilesional visual distraction in neglect. We also examine the relationship between optic ataxia and neglect by considering two illustrative cases, one with pure optic ataxia and the other with optic ataxia plus neglect, which reveal differences in the anatomical substrates of the two syndromes. We conclude that many patients with neglect make abnormal visually guided reaches, but the pattern of reaching deficits is highly variable, most likely reflecting heterogeneity of lesion location across subjects. Rather than being specific to the neglect syndrome, abnormalities of reaching in these patients may correspond to the extent of damage to the visuomotor control system which involves critical regions in both the parietal and frontal cortex, the white matter tracts connecting them and subcortical regions. Thus, the action control deficits in neglect may be conceptualised as a range of impairments affecting multiple stages in the visuomotor control process.

Functional specialization within the dorsolateral prefrontal cortex: a review of anatomical and physiological studies of non-human primates.

E Hoshi — 2007-04-14T00:13:12-00:00

Neurosci Res, Vol. 54, No. 2. (February 2006), pp. 73-84.

The dorsolateral prefrontal cortex (DLPFC) possesses cortico-cortical connections with the parietal and premotor cortices that are involved in visuomotor control of actions. Studies have shown that the DLPFC, especially the caudal part, has a crucial role in cognitive control of motor behavior, and that it uses spatial information in conjunction with information such as object identity, behavioral rules, and rewards. Current anatomical and physiological studies indicate that the DLPFC may not be a single entity. Anatomical studies show that preferential anatomical connections exist between subregions of the DLPFC and the parietal/premotor cortices. Physiological studies based on data obtained from monkeys performing a variety of cognitive tasks report region-specific neuronal activity within the DLPFC. In this article, I review evidence for functional segregation within the DLPFC and postulate that at least two distinct subregions, i.e., the dorsal and ventral parts, can be identified.

Attention, motor control and motor imagery in schizophrenia: implications for the role of the parietal cortex.

J Danckert — 2007-04-14T00:12:16-00:00

Schizophr Res, Vol. 70, No. 2-3. (1 October 2004), pp. 241-261.

Many recent models of schizophrenia have attempted to explain the so-called first-rank symptoms in terms of a breakdown in the self-monitoring of thoughts and behaviours. These models have focused on the most common symptom of schizophrenia auditory hallucinations-suggesting that they may represent disordered self-monitoring of internal speech. As such, much attention has been given to the role of the temporal and frontal cortices in the clinical presentation of patients with schizophrenia. In this review, we examine the role of the posterior parietal cortex (PPC) in schizophrenia within the context of recent models of self-monitoring deficits in these patients. Attentional dysfunctions and certain impairments of motor control and motor imagery all point towards the involvement of the parietal cortex in the disorder. In particular, we suggest that patients experiencing passivity phenomena (e.g., delusions of control) may have particular impairments of parietal function related to poor utilisation of forward models of intended actions. We also present a novel hypothesis that suggests differential impairments of the left and right parietal cortices in schizophrenia may help explain many of the first-rank symptoms of the disorder.

Visuo-motor integration and control in the human posterior parietal cortex: Evidence from TMS and fMRI.

M Iacoboni — 2006-10-24T18:38:24-00:00

Neuropsychologia, Vol. 44, No. 13. (2006), pp. 2691-2699.

The posterior parietal cortex is a fundamental structure for visuo-motor integration and control. Here I discuss recent transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) studies that I interpret as suggesting four concepts. The evolutionary process has enlarged the human posterior parietal cortex while still preserving the internal structure of the posterior parietal cortex of other primates. Visuo-motor control in the posterior parietal cortex may be implemented by coding primarily action goals. The lateralization of visuo-motor functions in the posterior parietal cortex suggests that the left posterior parietal cortex is more concerned with tool use and the right posterior parietal cortex is more concerned with imitation of the actions of others. Finally, visuo-motor inter-hemispheric transfer through parietal callosal fibers occurs at the level of 'motor intention'.

Compensatory cortical mechanisms in Parkinson's disease evidenced with fMRI during the performance of pre-learned sequential movements.

Rosella Mallol — 2007-04-14T00:04:32-00:00

Brain Res (27 February 2007)

We used fMRI to study brain activity associated with the performance of a pre-learned sequence of complex movements of the hand-made unimanually in a group of 13 Parkinson's disease patients and a group of 11 control volunteers. Patients were scanned "off" medication. In controls, sequential movements led to the activation of bilateral sensorimotor and premotor cortex, bilateral inferior parietal cortex, supplementary motor area, bilateral putamen and globus pallidus, and the left ventral lateral nucleus of the thalamus. Sequential movements in the Parkinson's disease group were associated with a similar pattern of activation, although relative decrease of activation in striatum and thalamic areas was observed. Patients in comparison with controls showed a hyperactivation in ipsilateral premotor areas and a hypoactivation in structures of the frontostriatal motor loop. Furthermore, patient scores in the motor scale of the UPDRS correlated positively with the activation thalamus and motor cortical areas during the sequential motor task. We concluded that in Parkinson's disease there is a compensatory mechanism of the dopamine deficit in frontostriatal motor circuits that increases participation in the execution of motor tasks of parietal-lateral premotor circuits.

Cognitive neuroscience: resolving conflict in and over the medial frontal cortex.

MF Rushworth — 2006-03-23T18:49:24-00:00

Curr Biol, Vol. 15, No. 2. (26 January 2005)

The medial surface of the brain's frontal lobe has been implicated both in the voluntary initiation of action and in monitoring actions in situations where several conflicting responses are possible. Recent work casts light on how these functions are parcelled out in the medial frontal cortex.

TMS in the parietal cortex: updating representations for attention and action.

MF Rushworth — 2007-04-13T21:56:48-00:00

Neuropsychologia, Vol. 44, No. 13. (2006), pp. 2700-2716.

Transcranial magnetic stimulation (TMS) is one of the most recent techniques to have been used in investigations of the parietal cortex but already a number of studies have employed it as a tool in investigations of attentional and sensorimotor processes in the human parietal cortices. The high temporal resolution of TMS has proved to be a particular strength of the technique and the experiments have led to hypotheses about when circumscribed regions of parietal cortex are critical for specific attentional and sensorimotor processes. A consistent theme that runs through many reports is that of a critical contribution of parietal areas when attention or movements are re-directed and representations for attention or action must be updated.

Changes in connectivity profiles define functionally distinct regions in human medial frontal cortex.

H Johansen-Berg — 2006-03-25T12:42:14-00:00

Proc Natl Acad Sci U S A, Vol. 101, No. 36. (7 September 2004), pp. 13335-13340.

A fundamental issue in neuroscience is the relation between structure and function. However, gross landmarks do not correspond well to microstructural borders and cytoarchitecture cannot be visualized in a living brain used for functional studies. Here, we used diffusion-weighted and functional MRI to test structure-function relations directly. Distinct neocortical regions were defined as volumes having similar connectivity profiles and borders identified where connectivity changed. Without using prior information, we found an abrupt profile change where the border between supplementary motor area (SMA) and pre-SMA is expected. Consistent with this anatomical assignment, putative SMA and pre-SMA connected to motor and prefrontal regions, respectively. Excellent spatial correlations were found between volumes defined by using connectivity alone and volumes activated during tasks designed to involve SMA or pre-SMA selectively. This finding demonstrates a strong relationship between structure and function in medial frontal cortex and offers a strategy for testing such correspondences elsewhere in the brain.

Role of the human medial frontal cortex in task switching: a combined fMRI and TMS study.

MF Rushworth — 2007-04-13T21:54:38-00:00

J Neurophysiol, Vol. 87, No. 5. (May 2002), pp. 2577-2592.

We used event-related functional magnetic resonance imaging (fMRI) to measure brain activity when subjects were performing identical tasks in the context of either a task-set switch or a continuation of earlier performance. The context, i.e., switching or staying with the current task, influenced medial frontal cortical activation; the medial frontal cortex is transiently activated at the time that subjects switch from one way of performing a task to another. Two types of task-set-switching paradigms were investigated. In the response-switching (RS) paradigm, subjects switched between different rules for response selection and had to choose between competing responses. In the visual-switching (VS) paradigm, subjects switched between different rules for stimulus selection and had to choose between competing visual stimuli. The type of conflict, sensory (VS) or motor (RS), involved in switching was critical in determining medial frontal activation. Switching in the RS paradigm was associated with clear blood-oxygenation-level-dependent signal increases ("activations") in three medial frontal areas: the rostral cingulate zone, the caudal cingulate zone, and the presupplementary motor area (pre-SMA). Switching in the VS task was associated with definite activation in just one medial frontal area, a region on the border between the pre-SMA and the SMA. Subsequent to the fMRI session, we used MRI-guided frameless stereotaxic procedures and repetitive transcranial magnetic stimulation (rTMS) to test the importance of the medial frontal activations for task switching. Applying rTMS over the pre-SMA disrupted subsequent RS performance but only when it was applied in the context of a switch. This result shows, first, that the pre-SMA is essential for task switching and second that its essential role is transient and limited to just the time of behavioral switching. The results are consistent with a role for the pre-SMA in selecting between response sets at a superordinate level rather than in selecting individual responses. The effect of the rTMS was not simply due to the tactile and auditory artifacts associated with each pulse; rTMS over several control regions did not selectively disrupt switching. Applying rTMS over the SMA/pre-SMA area activated in the VS paradigm did not disrupt switching. This result, first, confirms the limited importance of the medial frontal cortex for sensory attentional switching. Second, the VS rTMS results suggest that just because an area is activated in two paradigms does not mean that it plays the same essential role in both cases.

Interference with performance of a response selection task that has no working memory component: an rTMS comparison of the dorsolateral prefrontal and medial frontal cortex.

KA Hadland — 2007-04-13T21:53:57-00:00

J Cogn Neurosci, Vol. 13, No. 8. (15 November 2001), pp. 1097-1108.

It has been suggested that the dorsolateral prefrontal cortex (DLPFC) is involved in free selection (FS), the process by which subjects themselves decide what action to perform. Evidence for this proposal has been provided by imaging studies showing activation of the DLPFC when subjects randomly generate responses. However, these response selection tasks have a hidden working memory element and it has been widely reported that the DLPFC is activated when subjects perform tasks which involve working memory. The primary aim of this experiment was to establish if the DLPFC is genuinely involved in response selection. We used repetitive transcranial magnetic stimulation (rTMS) to investigate whether temporary interference of the DLPFC could disrupt performance of a response selection task that had no working memory component. Subjects performed tasks in which they made bimanual sequences of eight nonrepeating finger movements. In the FS task, subjects chose their movements at random while a computer monitor displayed these moves. This visual feedback obviated the need for subjects to maintain their previous moves "on-line." No selection was required for the two control tasks as responses were cued by the visual display. The attentional demands of the control tasks varied. In the high load (HL) version, subjects had to maintain their attention throughout the sequence, but this requirement was absent in the low load (LL) task. rTMS over the DLPFC slowed response times on the FS task and at the end of the sequence on the HL task, but had no effect on the LL task. rTMS over the medial frontal cortex (MFC) slowed response times on the FS task but had no effect on the HL task. This suggests that a response selection task without a working memory load will depend on the DLPFC and the MFC. The difference appears to be that the DLPFC is important when selecting between competing responses or when concentrating if there is a high attentional demand, but that the MFC is only important during the response selection task.

Mental maze solving: directional fMRI tuning and population coding in the superior parietal lobule.

P Gourtzelidis — 2005-10-07T16:35:14-00:00

Exp Brain Res, Vol. 165, No. 3. (September 2005), pp. 273-282.

The superior parietal lobule (SPL) of six human subjects was imaged at 4 T during mental traversing of a directed maze path. Here we demonstrate the orderly involvement of the SPL in this function, as follows. Forty-two percent of the voxels were tuned with respect to the direction of the maze path. This suggests a coherent tuning of local neuronal populations contributing to the change of the single-voxel BOLD signal. Preferred directions ranged throughout the directional continuum of 360 degrees . Voxels with similar preferred directions tended to cluster together: on average there were seven same-direction clusters per slice, with an average cluster membership of five voxels/cluster and an average nearest-neighbor same-direction intercluster distance of 13.1 mm. On the other hand, the average nearest-neighbor intercluster distance between a given direction and all other directions was 3.1 mm. This suggests a patchy arrangement such that patches of directionally tuned voxels, containing voxels with different preferred directions, alternate with patches of non-tuned voxels. Finally, the population vector predicted accurately the direction of the maze path (with an error of 12.7 degrees ), and provided good estimates (with an error of 29 degrees ) when calculated within parts of the SPL. Altogether, these findings document a new, orderly functional organization of the SPL with respect to mental tracing.

Direct evidence for a parietal-frontal pathway subserving spatial awareness in humans.

M Thiebaut de Schotten — 2007-04-10T05:07:46-00:00

Science, Vol. 309, No. 5744. (30 September 2005), pp. 2226-2228.

Intraoperative electrical stimulation, which temporarily inactivates restricted regions during brain surgery, can map cognitive functions in humans with spatiotemporal resolution unmatched by other methods. Using this technique, we found that stimulation of the right inferior parietal lobule or the caudal superior temporal gyrus, but not of its rostral portion, determined rightward deviations on line bisection. However, the strongest shifts occurred with subcortical stimulation. Fiber tracking identified the stimulated site as a section of the superior occipitofrontal fasciculus, a poorly known parietal-frontal pathway. These findings suggest that parietal-frontal communication is necessary for the symmetrical processing of the visual scene.

Spatial awareness is a function of the temporal not the posterior parietal lobe.

HO Karnath — 2007-04-10T05:03:18-00:00

Nature, Vol. 411, No. 6840. (21 June 2001), pp. 950-953.

Our current understanding of spatial behaviour and parietal lobe function is largely based on the belief that spatial neglect in humans (a lack of awareness of space on the side of the body contralateral to a brain injury) is typically associated with lesions of the posterior parietal lobe. However, in monkeys, this disorder is observed after lesions of the superior temporal cortex, a puzzling discrepancy between the species. Here we show that, contrary to the widely accepted view, the superior temporal cortex is the neural substrate of spatial neglect in humans, as it is in monkeys. Unlike the monkey brain, spatial awareness in humans is a function largely confined to the right superior temporal cortex, a location topographically reminiscent of that for language on the left. Hence, the decisive phylogenetic transition from monkey to human brain seems to be a restriction of a formerly bilateral function to the right side, rather than a shift from the temporal to the parietal lobe. One may speculate that this lateralization of spatial awareness parallels the emergence of an elaborate representation for language on the left side.