Rostral Inferior Parietal Lobule Research Articles

Complex tools and motor-to-mechanical transformations

The ability to use complex tools is thought to depend on multifaceted motor-to-mechanical transformations within the left inferior parietal lobule (IPL), linked to cognitive control over compound actions. Here we show using neuroimaging that demanding transformations of finger movements into proper mechanical movements of functional parts of complex tools invoke significantly the right rather than left rostral IPL, and bilateral posterior-to-mid and left anterior intraparietal sulci. These findings emerged during the functional grasp and tool-use programming phase. The expected engagement of left IPL was partly revealed by traditional region-of-interest analyses, and further modeling/estimations at the hand-independent level. Thus, our results point to a special role of right IPL in supporting sensory-motor spatial mechanisms which enable an effective control of fingers in skillful handling of complex tools. The resulting motor-to-mechanical transformations involve dynamic hand-centered to target-centered reference frame conversions indispensable for efficient interactions with the environment.

Human stereoEEG recordings reveal network dynamics of decision-making in a rule-switching task

The processing steps that lead up to a decision, i.e., the transformation of sensory evidence into motor output, are not fully understood. Here, we combine stereoEEG recordings from the human cortex, with single-lead and time-resolved decoding, using a wide range of temporal frequencies, to characterize decision processing during a rule-switching task. Our data reveal the contribution of rostral inferior parietal lobule (IPL) regions, in particular PFt, and the parietal opercular regions in decision processing and demonstrate that the network representing the decision is common to both task rules. We reconstruct the sequence in which regions engage in decision processing on single trials, thereby providing a detailed picture of the network dynamics involved in decision-making. The reconstructed timeline suggests that the supramarginal gyrus in IPL links decision regions in prefrontal cortex with premotor regions, where the motor plan for the response is elaborated.

The Positive Effect of Moderate-Intensity Exercise on the Mirror Neuron System: An fNIRS Study.

A growing number of studies have reported the beneficial effect of exercise on human social behavior. The mirror neuron system (MNS) plays a critical role in a variety of social behaviors from imitation to empathy. However, neuroimaging investigations into the effects of exercise on the MNS remain unexplored. To address this question, our study determined the effect of moderate-intensity exercise on the MNS using functional near-infrared spectroscopy (fNIRS). Specifically, 23 right-handed young individuals were asked to perform a table-setting task that included action execution and action observation before and after a 25-min exercise session on a cycle ergometer at moderate intensity (65% VO2peak). The control condition was the same task performed without exercise. Cortical hemodynamic changes in the four primary brain regions of the MNS were monitored with fNIRS, using a modified probe configuration that covered all four MNS regions in the left hemisphere. We used a region of interest (ROI)-based group analysis to determine which regions were activated during action execution and action observation. Following a session of moderate-intensity exercise, we found a significant increase in activation in all four MNS regions, namely the inferior frontal gyrus (IFG), premotor cortex (PMC), superior parietal lobule (SPL), and rostral inferior parietal lobule (IPL). This result indicated a positive effect of exercise on the MNS, specifically that moderate-intensity exercise could activate the MNS.

Functional connectivity during monitoring for visuomotor incongruence.

Previous human studies on monitoring for visuomotor incongruence emphasized the contribution of the fronto-parietal network and revealed significant activation of the right dorsolateral prefrontal cortex (DLPFC) and the right rostral inferior parietal lobule. Using functional MRI, this study investigated the brain regions involved in explicit monitoring for incongruence between motor intention and visual and/or proprioceptive information, particularly focusing on the fronto-parietal network. During in-phase bimanual movements, a static image of the participant's own hands was randomly inserted within real-time visual feedback of the movements to produce a mismatch between the actual performance and the visual input. The results of our task were similar to those of previous studies, in that greater activity was observed in the right DLPFC during incongruence conditions than during congruence conditions. However, the anatomical location of the DLPFC cluster was found in a more ventral region, compared with previous studies. Psychophysiological interaction analysis for the entire brain, using the right DLPFC as a seed region, indicated significantly greater functional connectivity with the bilateral dorsal premotor cortex, middle temporal gyri (area V5), and right rostral inferior parietal lobule (area PFt).

Feasibility of Functional Near-Infrared Spectroscopy (fNIRS) to Investigate the Mirror Neuron System: An Experimental Study in a Real-Life Situation.

The mirror neuron system (MNS), mainly including the premotor cortex (PMC), inferior frontal gyrus (IFG), superior parietal lobule (SPL), and rostral inferior parietal lobule (IPL), has attracted extensive attention as a possible neural mechanism of social interaction. Owing to high ecological validity, functional near-infrared spectroscopy (fNIRS) has become an ideal approach for exploring the MNS. Unfortunately, for the feasibility of fNIRS to detect the MNS, none of the four dominant regions were found in previous studies, implying a very limited capacity of fNIRS to investigate the MNS. Here, we adopted an experimental paradigm in a real-life situation to evaluate whether the MNS activity, including four dominant regions, can be detected by using fNIRS. Specifically, 30 right-handed subjects were asked to complete a table-setting task that included action execution and action observation. A double density probe configuration covered the four regions of the MNS in the left hemisphere. We used a traditional channel-based group analysis and also a ROI-based group analysis to find which regions are activated during both action execution and action observation. The results showed that the IFG, adjacent PMC, SPL, and IPL were involved in both conditions, indicating the feasibility of fNIRS to detect the MNS. Our findings provide a foundation for future research to explore the functional role of the MNS in social interaction and various disorders using fNIRS.

Development of rostral inferior parietal lobule area functional connectivity from late childhood to early adulthood

Although the mirror neuron system (MNS) has been extensively studied in monkeys and adult humans, very little is known about its development. Previous studies suggest that the MNS is present by infancy and that the brain and MNS-related cognitive abilities (such as language, empathy, and imitation learning) continue to develop after childhood. In humans, the PFt area of the inferior parietal lobule (IPL) seems to particularly correlate with the functional properties of the PF area in primates, which contains mirror neurons. However, little is known about the functional connectivity (FC) of the PFt area with other brain areas and whether these networks change over time. Here, we investigated the FC development of the PFt area-based network in 59 healthy subjects aged 7–26 years at resting-state to study brain development from late childhood through adolescence to early adulthood. The bilateral PFt showed similar core FC networks, which included the frontal lobe, the cingulate gyri, the insula, the somatosensory cortex, the precuneus, the superior and inferior parietal lobules, the temporal lobe, and the cerebellum posterior lobes. Furthermore, the FC between the left PFt and the left IPL exhibited a significantly positive correlation with age, and the FC between the left PFt and the right postcentral gyrus exhibited a significantly negative correlation with age. In addition, the FC between the right PFt and the right putamen exhibited a significantly negative correlation with age. Our findings suggest that the PFt area-based network develops and is reorganized with age.

Modulating the neural bases of persuasion: why/how, gain/loss, and users/non-users.

Designing persuasive content is challenging, in part because people can be poor predictors of their actions. Medial prefrontal cortex (MPFC) activation during message exposure reliably predicts downstream behavior, but past work has been largely atheoretical. We replicated past results on this relationship and tested two additional framing effects known to alter message receptivity. First, we examined gain- vs. loss-framed reasons for a health behavior (sunscreen use). Consistent with predictions from prospect theory, we observed greater MPFC activity to gain- vs. loss-framed messages, and this activity was associated with behavior. This relationship was stronger for those who were not previously sunscreen users. Second, building on theories of action planning, we compared neural activity during messages regarding how vs. why to enact the behavior. We observed rostral inferior parietal lobule and posterior inferior frontal gyrus activity during action planning (“how” messages), and this activity was associated with behavior; this is in contrast to the relationship between MPFC activity during the “why” (i.e., gain and loss) messages and behavior. These results reinforce that persuasion occurs in part via self-value integration—seeing value and incorporating persuasive messages into one's self-concept—and extend this work to demonstrate how message framing and action planning may influence this process.

Expert–novice differences in brain function of field hockey players

The aims of this study were to use functional magnetic resonance imaging to examine the neural bases for perceptual-cognitive superiority in a hockey anticipation task. Thirty participants (15 hockey players, 15 non-hockey players) lay in an MRI scanner while performing a video-based task in which they predicted the direction of an oncoming shot in either a hockey or a badminton scenario. Video clips were temporally occluded either 160ms before the shot was made or 60ms after the ball/shuttle left the stick/racquet. Behavioral data showed a significant hockey expertise×video-type interaction in which hockey experts were superior to novices with hockey clips but there were no significant differences with badminton clips. The imaging data on the other hand showed a significant main effect of hockey expertise and of video type (hockey vs. badminton), but the expertise×video-type interaction did not survive either a whole-brain or a small-volume correction for multiple comparisons. Further analysis of the expertise main effect revealed that when watching hockey clips, experts showed greater activation in the rostral inferior parietal lobule, which has been associated with an action observation network, and greater activation than novices in Brodmann areas 17 and 18 and middle frontal gyrus when watching badminton videos. The results provide partial support both for domain-specific and domain-general expertise effects in an action anticipation task.

The Neuroscience of Inspirational Leadership: The Importance of Collective-Oriented Language and Shared Group Membership

Effective leaders are believed to inspire followers by providing inclusive visions of the future that followers can identify with. In the present study, we examined the neural mechanisms underlying this process, testing key hypotheses derived from transformational and social identity approaches to leadership. While undergoing functional MRI, supporters from the two major Australian political parties (Liberal vs. Labor) were presented with inspirational collective-oriented and noninspirational personal-oriented statements made by in-group and out-group leaders. Imaging data revealed that inspirational (rather than noninspirational) statements from in-group leaders were associated with increased activation in the bilateral rostral inferior parietal lobule, pars opercularis, and posterior midcingulate cortex: brain areas that are typically implicated in controlling semantic information processing. In contrast, for out-group leaders, greater activation in these areas was associated with noninspirational statements. In addition, noninspirational statements by in-group (but not out-group) leaders resulted in increased activation in the medial prefrontal cortex, an area typically associated with reasoning about a person’s mental state. These results show that followers processed identical statements qualitatively differently as a function of leaders’ group membership, thus demonstrating that shared identity acts as an amplifier for inspirational leadership communication.

Functional Dissociations Within Posterior Parietal Cortex During Scene Integration and Viewpoint Changes.

The posterior parietal cortex (PPC) is an anatomically heterogeneous brain region implicated in a wide range of cognitive operations, including egocentric spatial processing and both short- and long-term memory. Here, we report functional specificities of cytoarchitectonically defined subregions of PPC during the processing of scenes across changes in viewpoint. Participants (n = 16) saw photographs of familiar and unfamiliar places while undergoing functional magnetic resonance imaging (fMRI). On each trial, 4 viewpoints of the same place were presented, with either a plausible sequence of viewpoints (SEQ) or a scrambled order (SCRA). Distinct response profiles were observed within PPC. Area 7A showed increased activity for SEQ versus SCRA order, regardless of place familiarity, whereas the rostral inferior parietal lobule showed preferential increases for unfamiliar versus familiar places in SEQ series. In contrast, more posterior subregions in both superior and inferior PPC exhibited increases for familiar versus unfamiliar places at the end of the sequence, regardless of order. The data highlight the distinctive contribution of several subregions of PPC during the processing of scenes, with specific cortical areas involved in the progressive integration of spatial information across viewpoint changes, and others involved in the retrieval and maintenance of scene information in memory.

Neural processing of sensory and emotional-communicative information associated with the perception of vicarious pain

The specific neural processes underlying vicarious pain perception are not fully understood. In this functional imaging study, 20 participants viewed pain-evoking or neutral images displaying either sensory or emotional-communicative information. The pain images displayed nociceptive agents applied to the hand or the foot (sensory information) or facial expressions of pain (emotional-communicative information) and were matched with their neutral counterparts. Combining pain-evoking and neutral images showed that body limbs elicited greater activity in sensory motor regions, whereas midline frontal and parietal cortices and the amygdala responded more strongly to faces. The pain-evoking images elicited greater activity than their neutral counterparts in the bilateral inferior frontal gyrus (IFG), the left inferior parietal lobule (IPL) and the bilateral extrastriate body area. However, greater pain-related activity was observed in the rostral IPL when images depicted a hand or foot compared to a facial expression of pain, suggesting a more specific involvement in the coding of somato-motor information. Posterior probability maps enabling Bayesian inferences further showed that the anterior IFG (BA 45 and 47) was the only region showing no intrinsic probability of activation by the neutral images, consistent with a role in the extraction of the meaning of pain-related visual cues. Finally, inter-individual empathy traits correlated with responses in the supracallosal mid/anterior cingulate cortex and the anterior insula when pain-evoking images of body limbs or facial expressions were presented, suggesting that these regions regulated the observer's affective-motivational response independent from the channels from which vicarious pain is perceived.

Grasping-Related Functional Magnetic Resonance Imaging Brain Responses in the Macaque Monkey

Research in recent decades has suggested the existence of a dedicated brain network devoted to the organization and execution of grasping, one of the most important and skilled movements of primates. Grasping an object requires the transformation of intrinsic object properties such as size, orientation, and shape into an appropriate motor scheme shaping the hand. Although electrophysiological recordings in the monkey model have proven invaluable for gaining insights into the neuronal substrate underlying this complex behavior, knowledge concerning the existence and organization of a similar system in the human brain is derived mainly from imaging studies. Here, we present for the first time functional magnetic resonance imaging (fMRI) of brain activity while macaque monkeys performed reaching and grasping movements in a 3 tesla MR scanner. Grasping in the dark (compared with reaching) yielded significant activations in anterior intraparietal area and ventral premotor area F5, in addition to area PFG in the rostral inferior parietal lobule, somatosensory areas (SI, SII, area 5), and the hand field of F1. Whole-brain macaque fMRI motor studies will be instrumental in establishing possible homologies concerning grasping organization in the human and monkey brains, bridging the gap between human imaging and monkey electrophysiology.

Evidence for context sensitivity of grasp representations in human parietal and premotor cortices

Grasp-related responses in neurons of the macaque rostral inferior parietal lobule [PF/PFG and the anterior intraparietal area (AIP)] are modulated by task context. Event-related functional MRI was used to determine whether this is true in putative homologs of the human cortex, the rostral inferior parietal lobule (rIPL) and the anterior intraparietal sulcus (aIPS). Fifteen healthy, right-handed adults were required to select prospectively the most comfortable way to grasp a horizontally oriented handle using the cued hand (left or right). In the "no-rotation" condition, the task was simply to grasp the handle, whereas in the "rotation" condition, the goal was to plan to grasp and rotate it into a vertical orientation with the cued end (medial or lateral) pointing downward. In both conditions, participants remained still and indicated their grip preferences by pressing foot pedals. As in overt grasping, participants' grip preferences were significantly influenced by anticipation of the demands associated with handle rotation. Activity within the aIPS and rIPL increased bilaterally in both the rotation and no-rotation conditions. Importantly, these responses were significantly greater in the rotation vs. no-rotation condition. Similar context effects were detected in the presupplementary motor area, caudal intraparietal sulcus/superior parietal lobule, and bilateral dorsal and left ventral premotor cortices. Grasp representations within the rIPL and aIPS are sensitive to predicted task demands and play a role in context-sensitive grip selection. Moreover, the findings provide additional evidence that areas involved in the sensorimotor control of grasp also contribute to feedforward planning.

Dissociating the Human Language Pathways with High Angular Resolution Diffusion Fiber Tractography

The anatomical connectivity of ventrolateral frontal areas 44 and 45, which in the human brain constitute Broca's region, has been revisited on the basis of experimental anatomical tracer evidence in the nonhuman primate that the homologues of areas 44 and 45 have distinct bidirectional corticocortical connections. Here we show, using high angular resolution diffusion imaging in the living human brain, a dissociation between the specific projections from the pars opercularis (area 44) and the pars triangularis (area 45) in the ventrolateral frontal lobe. As in the macaque monkey, area 44 has distinct connections with the rostral inferior parietal lobule via the third branch of the superior longitudinal fasciculus. In contrast, area 45 connects with the superior temporal gyrus, anterior to Heschl's gyrus, via the extreme capsule fiber system. These results highlight the differences in connectivity between areas 44 and 45 which had previously been thought to be uniformly connected with the posterior temporal region via the arcuate fasciculus. We also provide evidence in the human brain that the arcuate fasciculus, as in the macaque monkey brain, connects the posterior superior temporal region with dorsolateral frontal areas 8 and rostral 6 that lie above areas 44 and 45. Thus, monkey and human evidence suggests that the connections of areas 44 and 45 are much more differentiated than had previously been thought and provide the basis for studies searching for their differential contribution in function.

Ventrolateral prefrontal cortex and tactile memory disambiguation in the human brain

Tactile sensory information is first channeled from the primary somatosensory cortex on the postcentral gyrus to the parietal opercular region (i.e., the secondary somatosensory cortex) and the rostral inferior parietal lobule and, from there, to the prefrontal cortex, with which bidirectional connections exist. Although we know that tactile memory signals can be found in the prefrontal cortex, the contribution of the different prefrontal areas to tactile memory remains unclear. The present functional MRI study shows that a specific part of the prefrontal cortex in the human brain, namely the midventrolateral prefrontal region (cytoarchitectonic areas 47/12 and 45), is involved in active controlled retrieval processing necessary for the disambiguation of vibrotactile information in short-term memory. Furthermore, we demonstrate that this particular part of the prefrontal cortex interacts functionally with the secondary somatosensory areas in the parietal operculum and the rostral inferior parietal lobule during controlled processing for the retrieval of specific tactile information.

An fMRI approach to particularize the frontoparietal network for visuomotor action monitoring: Detection of incongruence between test subjects’ actions and resulting perceptions

Contemporary theories of motor control assume that motor actions underlie a supervisory control system which utilizes reafferent sensory feedbacks of actions for comparison with the original motor programs. The functional network of visuomotor action monitoring is considered to include inferior parietal, lateral and medial prefrontal cortices. To study both sustained monitoring for visuomotor incongruence and the actual detection of incongruence, we used a hybrid fMRI epoch-/event-related design. The basic experimental task was a continuous motor task, comprising a simple racing game. Within certain blocks of this task, incongruence was artificially generated by intermittent takeover of control over the car by the computer. Fifteen male subjects were instructed to monitor for incongruence between their own and the observed actions in order to abstain from their own action whenever the computer took over control. As a result of both sustained monitoring and actual detection of visuomotor incongruence, the rostral inferior parietal lobule displayed a BOLD signal increase. In contrast, the prefrontal cortex (PFC) exhibited two different activation patterns. Dorsolateral (BA 9/46) and medial/cingulate (BA 8, BA 32) areas of the PFC displayed a greater increase of activation in sustained monitoring, while ventrolateral PFC showed greater event-related activation for the actual detection of visuomotor incongruence. Our results suggest that the rostral inferior parietal lobule is specifically involved in the reafferent comparison of the test subjects’ own actions and visually perceived actions. Different activation patterns of the PFC may reflect different frontoparietal networks for sustained action monitoring and actual detection of reafferent incongruence.

Efferent association pathways originating in the caudal prefrontal cortex in the macaque monkey

The efferent association fibers from the caudal part of the prefrontal cortex to posterior cortical areas course via several pathways: the three components of the superior longitudinal fasciculus (SLF I, SLF II, and SLF III), the arcuate fasciculus (AF), the fronto-occipital fasciculus (FOF), the cingulate fasciculus (CING F), and the extreme capsule (Extm C). Fibers from area 8Av course via FOF and SLF II, merging in the white matter of the inferior parietal lobule (IPL) and terminating in the caudal intraparietal sulcus (IPS). A group of these fibers turns ventrally to terminate in the caudal superior temporal sulcus (STS). Fibers from the rostral part of area 8Ad course via FOF and SLF II to the IPS and IPL and via the AF to the caudal superior temporal gyrus and STS. Some fibers from the rostral part of area 8Ad are conveyed to the medial parieto-occipital region via FOF, to the STS via Extm C, and to the caudal cingulate gyrus via CING F. Fibers from area 8B travel via SLF I to the supplementary motor area and area 31 in the caudal dorsal cingulate region and via the CING F to cingulate areas 24 and 23 and the cingulate motor areas. Fibers from area 9/46d course via SLF I to the superior parietal lobule and medial parieto-occipital region, via SLF II to the IPL. Fibers from area 9/46v travel via SLF III to the rostral IPL and the frontoparietal opercular region and via the CING F to the cingulate gyrus.

Connections of the ventral granular frontal cortex of macaques with perisylvian premotor and somatosensory areas: anatomical evidence for somatic representation in primate frontal association cortex.

In macaque monkeys with injections of tritiated amino acids or horseradish peroxidase in the ventrolateral granular frontal cortex, we observed extensive anterograde and retrograde labeling of the premotor and somatosensory cortex in and around the lateral sulcus. Comparable labeling was not present with large and small control injections of the dorsal granular cortex. Cytoarchitectonic evaluation of the perisylvian cortex in the three cases examined in detail indicated that labeled areas included the ventral premotor cortex (area 6V); the precentral opercular and orbitofrontal opercular areas (PrCO and OFO); the second somatosensory area (S-II); the opercular cortex immediately anterior to S-II, possibly corresponding to area 2 of the S-I complex; and the central part of the insular cortex, including portions of the granular and dysgranular insular fields (Ig, Idg). Labeling was particularly dense and extensive in areas 6V, S-II, and OFO. Lighter labeling was also present in the rostral inferior parietal lobule (areas 7b and POa). The distribution of label within perisylvian areas was not uniform: certain parts were heavily labeled, while other parts were lightly labeled or unlabeled. Comparison of label distribution with published accounts of the somatotopy of these areas indicates that forelimb and orofacial representations were selectively labeled. Further, our results, taken together with other recent anatomical findings (e.g., Matelli et al.: Journal of Comparative Neurology 251:281-298, 1987; Barbas and Pandya: Journal of Comparative Neurology 256:211-228, 1987) suggest strongly that there is a network of interconnected forelimb and orofacial representations in macaque cortex, involving the ventral granular frontal cortex, area 6V, OFO, opercular area 2, S-II, the central insula, and area 7b. Each injection of frontal cortex which labeled the perisylvian somatic cortex involved the cortex of the ventral rim of the principal sulcus (PSvr). The cortex surrounding the PSvr does not stand out as a distinct area in Nissl-stained material. However, examination of myelin-stained sections prepared from uninjected hemispheres with the Gallyas technique revealed the existence of a distinct zone centered on the PSvr. This myeloarchitectonic area, which we term area 46vr, is more heavily myelinated than the ventral bank and fundus of the principal sulcus (area 46v) but is less heavily myelinated than the ventral (inferior) convexity (area 12). Involvement of area 46vr in our injections was probably responsible for the strong labeling observed in perisylvian somatic areas.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of lesions of superior temporal gyrus and inferior parietal lobe on temporal and vertex components of the human AEP

We recorded auditory evoked potentials (AEPs) to 1 kHz tone bursts in controls and patients with unilateral lesions centered in posterior superior temporal gyrus and adjacent caudal inferior parietal lobule (STG) or in rostral inferior parietal lobule (IPL). Controls generated a vertex maximal N94 (N1b) and P200 (P2) and additional P45, N78 and N127 temporal AEP components (P45, N1a, N1c). Similar to prior reports, in controls the N1a was most prominent over the left temporal lobe and the P45 was largest over the right temporal lobe consistent with behavioral and anatomical data indicating differential organization of left and right human temporal lobe. The N1c was recorded equally from both T 3 and T 4 electrodes and was enhanced in the temporal site contralateral to the ear of stimulation. The patient groups had differenti al effects on AEPs. Unilateral STG lesions resulted in bilateral reductions of the N1b and P45 and marked unilateral reductions of the N1a and N1c over lesioned hemisphere. IPL lesions resulted in bilateral but non-significant reductions of the N1b and N1c. The scalp topography results in normal subjects combined with the effects of unilateral STG lesions provide supportive evidence that the temporal maximal components of the human AEP (P45, N1a, N1c) are generated by radially oriented neuronal dipole sources located in STG. The bilateral reduction of the N1b vertex response by unilateral STG lesions is compatible with a unilateral disruption of a vertically oriented dipole situated in the posterior superior temporal plane. The results emphasize the critical role of the superior temporal plane and lateral superior temporal gyrus in generation of human long latency AEPs.

Effects of lesions of temporal-parietal junction on perceptual and attentional processing in humans

When stimuli with larger forms (global) containing smaller forms (local) are presented to subjects with large lesions in the right hemisphere, they are more likely to miss the global form than the local form, whereas subjects with large lesions in the left are more likely to miss the local than the global form. The present study tested whether the global/local impairment in subjects with posterior lesions was due to deficits in controlled attentional processes, passive perceptual processes, or both. Attentional control was examined by measuring reaction time changes when the probability of a target appearing at either the global or local level was varied. Patients with unilateral right or left lesions centered in temporal-parietal regions and age-matched controls served as subjects. Because neurophysiological and neuropsychological evidence have implicated temporal regions in visual discrimination and inferior parietal regions in the allocation of attention to locations in the visual field, patients with left hemisphere lesions were further subdivided into those with lesions centered in the superior temporal gyrus (LSTG) or rostral inferior parietal lobule (LIPL). Patients with right hemisphere injury could not be analogously subdivided. The results revealed that the LSTG group was able to control the allocation of attention to global and local levels normally, while the LIPL group was not. In contrast, the LSTG group showed a strong baseline reaction time advantage toward global targets, while normals and the LIPL group showed no advantage toward one level or the other. Finally, the perceptual component was affected differentially by lesions in the right hemisphere and LSTG, with lesions in the left favoring global targets and lesions in the right favoring local targets. These findings indicate that the hemispheric global/local asymmetry is due to a perceptual mechanism with a critical anatomical locus centered in the STG.