Localization of human intraparietal areas AIP, CIP, and LIP using surface orientation and saccadic eye movement tasks

Hand constraint reduces brain activity and affects the speed of verbal responses on semantic tasks

According to the theory of embodied cognition, semantic processing is closely coupled with body movements. For example, constraining hand movements inhibits memory for objects that can be manipulated with the hands. However, it has not been confirmed whether body constraint reduces brain activity related to semantics. We measured the effect of hand constraint on semantic processing in the parietal lobe using functional near-infrared spectroscopy. A pair of words representing the names of hand-manipulable (e.g., cup or pencil) or nonmanipulable (e.g., windmill or fountain) objects were presented, and participants were asked to identify which object was larger. The reaction time (RT) in the judgment task and the activation of the left intraparietal sulcus (LIPS) and left inferior parietal lobule (LIPL), including the supramarginal gyrus and angular gyrus, were analyzed. We found that constraint of hand movement suppressed brain activity in the LIPS toward hand-manipulable objects and affected RT in the size judgment task. These results indicate that body constraint reduces the activity of brain regions involved in semantics. Hand constraint might inhibit motor simulation, which, in turn, would inhibit body-related semantic processing.

Visual task-related functional and structural magnetic resonance imaging for the objective quantitation of visual function in patients with advanced retinitis pigmentosa

Purpose

The objective quantitation of visual function in patients with advanced retinitis pigmentosa (RP) presents a difficult challenge due to the weak visual function of these patients. This study utilized magnetic resonance imaging (MRI) to assess the function and structure of the visual cortex (VC) in patients with RP and quantitatively categorize them.

Materials and Methods

Twenty-three patients with RP and ten healthy controls (HCs) were enrolled for MRI examinations. The patients were divided into form perception (FP) and no form perception (NFP) groups. Participants underwent structural MRI scans, and two visual task functional MRI scans were performed using stimuli, including white flash and black and white checkerboard patterns. Eight regions of interest (ROIs) were studied. In structural MRI, the gray matter volume (GMV) was compared in the ROIs. In the two visual tasks, the response intensity and functional connectivity (FC) of ROIs were also compared separately. Correlation analysis was performed to explore the correlations between the structural and functional parameters.

Results

In the structural analysis, the GMV in Brodmann areas 17, 18, and 19 of the FP and NFP groups was significantly lower than that of HCs. Regarding the functional data, the response intensity in the VC of both the FP and NFP groups was significantly lower than that in HCs. The response in Brodmann areas 17, 18, and 19 obtained using the pattern stimulus was significantly lower in the NFP group than in the FP group. For the FC comparison, the FP and NFP groups exhibited significantly lower values in several pathways than the HCs, and FC in the ipsilateral V1–contralateral V1 pathway in the flash task was significantly lower in the NFP group than in the FP group. A positive correlation between response intensity and GMV was observed in Brodmann areas 17, 18, and 19 in both flash and pattern visual tasks.

Conclusion

Magnetic resonance imaging was an effective tool to objectively and quantitatively evaluate the visual function of patients with advanced RP. Response intensity and FC were effective parameters to distinguish FP and NFP patients. A positive correlation between response intensity and GMV was observed in the VC.

General and Specific Effects of Stereo Learning

Technological advancements in virtual reality challenge the human vision, especially stereopsis, a function, which characterizes how two eyes coordinate to form a unified three-dimensional (3D) representation of the external world and is found to be deficient in 30% of the normal population. Although a few previous studies have consistently found that the perceptual learning of stereopsis significantly improved stereoacuity, an underlying mechanism of stereo learning remains heavily debated. Here, we trained subjects with normal stereo vision (assessed with the FLY Stereo Acuity Test) to judge stereopsis containing three types of binocular disparity orders (i.e., zero-, first-, and second-order), aiming to systematically examine the characteristics and plasticity of stereo learning. Thirty subjects were randomly assigned to the three training groups (each for the zero-, first-, or second-order disparity separately). The disparity thresholds were measured before and after training. The disparity threshold was measured in 10 additional control subjects only at the pre- and post-training phase. Stereoscopic images were displayed through a shutter goggle, which is synchronized to a monitor. We found that the training significantly improved the zero-, first-, and second-order disparity threshold by 52.42, 36.28, and 14.9% in the zero-order training condition; 30.44, 63.74, and 21.07% in the first-order training condition; and 30.77, 25.19, and 75.12% in the second-order training condition, respectively. There was no significant improvement in the control group. Interestingly, the greatest improvements in the first- and second-order disparity threshold were found in the corresponding disparity training group; on the contrary, the improvements in the zero-order disparity threshold were comparable across all the three disparity training groups. Our findings demonstrated both general (related to the zero-order disparity) and specific improvements (related to the first- and second-order disparity) in stereo learning, suggesting that stereo training occurs at different visual processing stages and its effects might depend on the specific training sites.

Wide-field retinotopy reveals a new visuotopic cluster in macaque posterior parietal cortex

We investigated the visuotopic organization of macaque posterior parietal cortex (PPC) by combining functional imaging (fMRI) and wide-field retinotopic mapping in two macaque monkeys. Whole brain blood-oxygen-level-dependent (BOLD) signal was recorded while monkeys maintained central fixation during the presentation of large rotating wedges and expending/contracting annulus of a "shaking" fruit basket, designed to maximize the recruitment of PPC neurons. Results of the surface-based population receptive field (pRF) analysis reveal a new cluster of four visuotopic areas at the confluence of the parieto-occipital and intra-parietal sulci, in a location previously defined histologically and anatomically as the posterior intra-parietal (PIP) region. This PIP cluster groups together two recently described areas (CIP1/2) laterally and two newly identified ones (PIP1/2) medially, whose foveal representations merge in the fundus of the intra-parietal sulcus. The cluster shares borders with other visuotopic areas: V3d posteriorly, V3A/DP laterally, V6/V6A medially and LIP anteriorly. Together, these results show that monkey PPC is endowed with a dense set of visuotopic areas, as its human counterpart. The fact that fMRI and wide-field stimulation allows a functional parsing of monkey PPC offers a new framework for studying functional homologies with human PPC.

Stereomotion Processing in the Nonhuman Primate Brain

The cortical areas that process disparity-defined motion-in-depth (i.e., cyclopean stereomotion [CSM]) were characterized with functional magnetic resonance imaging (fMRI) in two awake, behaving macaques. The experimental protocol was similar to previous human neuroimaging studies. We contrasted the responses to dynamic random-dot patterns that continuously changed their binocular disparity over time with those to a control condition that shared the same properties, except that the temporal frames were shuffled. A whole-brain voxel-wise analysis revealed that in all four cortical hemispheres, three areas showed consistent sensitivity to CSM. Two of them were localized respectively in the lower bank of the superior temporal sulcus (CSMSTS) and on the neighboring infero-temporal gyrus (CSMITG). The third area was situated in the posterior parietal cortex (CSMPPC). Additional regions of interest-based analyses within retinotopic areas defined in both animals indicated weaker but significant responses to CSM within the MT cluster (most notably in areas MSTv and FST). Altogether, our results are in agreement with previous findings in both human and macaque and suggest that the cortical areas that process CSM are relatively well preserved between the two primate species.

What Role Does "Elongation" Play in "Tool-Specific" Activation and Connectivity in the Dorsal and Ventral Visual Streams?

Images of tools induce stronger activation than images of nontools in a left-lateralized network that includes ventral-stream areas implicated in tool identification and dorsal-stream areas implicated in tool manipulation. Importantly, however, graspable tools tend to be elongated rather than stubby, and so the tool-selective responses in some of these areas may, to some extent, reflect sensitivity to elongation rather than "toolness" per se. Using functional magnetic resonance imaging, we investigated the role of elongation in driving tool-specific activation in the 2 streams and their interconnections. We showed that in some "tool-selective" areas, the coding of toolness and elongation coexisted, but in others, elongation and toolness were coded independently. Psychophysiological interaction analysis revealed that toolness, but not elongation, had a strong modulation of the connectivity between the ventral and dorsal streams. Dynamic causal modeling revealed that viewing tools (either elongated or stubby) increased the connectivity from the ventral- to the dorsal-stream tool-selective areas, but only viewing elongated tools increased the reciprocal connectivity between these areas. Overall, these data disentangle how toolness and elongation affect the activation and connectivity of the tool network and help to resolve recent controversies regarding the relative contribution of "toolness" versus elongation in driving dorsal-stream "tool-selective" areas.

Action and object words are differentially anchored in the sensory motor system - A perspective on cognitive embodiment

Embodied and grounded cognition theories have assumed that the sensorimotor system is causally involved in processing motor-related language content. Although a causal proof on a single-cell basis is ethically not possible today, the present fMRI study provides confirmation of this longstanding speculation, as far as it is possible with recent methods, employing a new computational approach. More specifically, we were looking for common activation of nouns and objects, and actions and verbs, representing the canonical and mirror neuron system, respectively. Using multivariate pattern analysis, a resulting linear classifier indeed successfully generalized from distinguishing actions from objects in pictures to distinguishing the respective verbs from nouns in written words. Further, these action-related pattern responses were detailed by recently introduced predictive pattern decomposition into the constituent activity atoms and their relative contributions. The findings support the concept of canonical neurons and mirror neurons implementing embodied processes with separate roles in distinguishing objects from actions, and nouns from verbs, respectively. This example of neuronal recycling processing algorithms is consistent with a multimodal brain signature of human action and object concepts. Embodied language theory is thus merged with actual neurobiological implementation.

Processing of Egomotion-Consistent Optic Flow in the Rhesus Macaque Cortex

The cortical network that processes visual cues to self-motion was characterized with functional magnetic resonance imaging in 3 awake behaving macaques. The experimental protocol was similar to previous human studies in which the responses to a single large optic flow patch were contrasted with responses to an array of 9 similar flow patches. This distinguishes cortical regions where neurons respond to flow in their receptive fields regardless of surrounding motion from those that are sensitive to whether the overall image arises from self-motion. In all 3 animals, significant selectivity for egomotion-consistent flow was found in several areas previously associated with optic flow processing, and notably dorsal middle superior temporal area, ventral intra-parietal area, and VPS. It was also seen in areas 7a (Opt), STPm, FEFsem, FEFsac and in a region of the cingulate sulcus that may be homologous with human area CSv. Selectivity for egomotion-compatible flow was never total but was particularly strong in VPS and putative macaque CSv. Direct comparison of results with the equivalent human studies reveals several commonalities but also some differences.

Disentangling Representations of Object and Grasp Properties in the Human Brain

The properties of objects, such as shape, influence the way we grasp them. To quantify the role of different brain regions during grasping, it is necessary to disentangle the processing of visual dimensions related to object properties from the motor aspects related to the specific hand configuration. We orthogonally varied object properties (shape, size, and elongation) and task (passive viewing, precision grip with two or five digits, or coarse grip with five digits) and used representational similarity analysis of functional magnetic resonance imaging data to infer the representation of object properties and hand configuration in the human brain. We found that object elongation is the most strongly represented object feature during grasping and is coded preferentially in the primary visual cortex as well as the anterior and posterior superior-parieto-occipital cortex. By contrast, primary somatosensory, motor, and ventral premotor cortices coded preferentially the number of digits while ventral-stream and dorsal-stream regions coded a mix of visual and motor dimensions. The representation of object features varied with task modality, as object elongation was less relevant during passive viewing than grasping. To summarize, this study shows that elongation is a particularly relevant property of the object to grasp, which along with the number of digits used, is represented within both ventral-stream and parietal regions, suggesting that communication between the two streams about these specific visual and motor dimensions might be relevant to the execution of efficient grasping actions.

SIGNIFICANCE STATEMENT

To grasp something, the visual properties of an object guide preshaping of the hand into the appropriate configuration. Different grips can be used, and different objects require different hand configurations. However, in natural actions, grip and object type are often confounded, and the few experiments that have attempted to separate them have produced conflicting results. As such, it is unclear how visual and motor properties are represented across brain regions during grasping. Here we orthogonally manipulated object properties and grip, and revealed the visual dimension (object elongation) and the motor dimension (number of digits) that are more strongly coded in ventral and dorsal streams. These results suggest that both streams play a role in the visuomotor coding essential for grasping.

The Intersection between Ocular and Manual Motor Control: Eye-Hand Coordination in Acquired Brain Injury

Acute and chronic disease processes that lead to cerebral injury can often be clinically challenging diagnostically, prognostically, and therapeutically. Neurodegenerative processes are one such elusive diagnostic group, given their often diffuse and indolent nature, creating difficulties in pinpointing specific structural abnormalities that relate to functional limitations. A number of studies in recent years have focused on eye-hand coordination (EHC) in the setting of acquired brain injury (ABI), highlighting the important set of interconnected functions of the eye and hand and their relevance in neurological conditions. These experiments, which have concentrated on focal lesion-based models, have significantly improved our understanding of neurophysiology and underscored the sensitivity of biomarkers in acute and chronic neurological disease processes, especially when such biomarkers are combined synergistically. To better understand EHC and its connection with ABI, there is a need to clarify its definition and to delineate its neuroanatomical and computational underpinnings. Successful EHC relies on the complex feedback- and prediction-mediated relationship between the visual, ocular motor, and manual motor systems and takes advantage of finely orchestrated synergies between these systems in both the spatial and temporal domains. Interactions of this type are representative of functional sensorimotor control, and their disruption constitutes one of the most frequent deficits secondary to brain injury. The present review describes the visually mediated planning and control of eye movements, hand movements, and their coordination, with a particular focus on deficits that occur following neurovascular, neurotraumatic, and neurodegenerative conditions. Following this review, we also discuss potential future research directions, highlighting objective EHC as a sensitive biomarker complement within acute and chronic neurological disease processes.

Approaching the Atrium Through the Intraparietal Sulcus: Mapping the Sulcal Morphology and Correlating the Surgical Corridor to Underlying Fiber Tracts

BACKROUND: Although the operative corridor used during the intraparietal transsulcal approach to the atrium has been previously investigated, most anatomical studies focus on its relationship to the optic radiations.

OBJECTIVE: To study the intraparietal sulcus (IPS) morphology and to explore the subcortical anatomy with regard to the surgical trajectory used during the intraparietal transsulcal tranventricular approach.

METHODS: Twenty-five adult, formalin fixed, cerebral hemispheres were investigated. Fifteen underwent the Klingler procedure and were dissected in a lateromedial direction using the fiber microdissection technique. The trajectory of the dissection resembled that of real operative settings. The remaining 10 hemispheres were cut along the longitudinal axis of the sulcus in order to correlate its surface anatomy to corresponding parts of the ventricular system.

RESULTS: IPS demonstrated an interrupted course in 36% of the specimens while its branching pattern was variable. The sulcus anterior half was found to overly the atrium in all occasions. Four discrete, consecutive white matter layers were identified en route to the atrium, ie, the arcuate fibers, the arcuate segment of the superior longitudinal fasciculus, the corona radiata and tapetum, with the arcuate segment being near to the dissection trajectory.

CONCLUSION: Given the angle of brain transgression during the intraparietal approach, we found the optimal dissection area to be the very middle of the sulcus. The IPS–postcentral sulcus meeting point, in contrast to previous thought, proved to risk potential injury to the arcuate segment of the superior longitudinal fasciculus, thus affecting surgical outcome.

Functional interactions between the macaque dorsal and ventral visual pathways during three-dimensional object vision

The division of labor between the dorsal and the ventral visual stream in the primate brain has inspired numerous studies on the visual system in humans and in nonhuman primates. However, how and under which circumstances the two visual streams interact is still poorly understood. Here we review evidence from anatomy, modelling, electrophysiology, electrical microstimulation (EM), reversible inactivation and functional imaging in the macaque monkey aimed at clarifying at which levels in the hierarchy of visual areas the two streams interact, and what type of information might be exchanged between the two streams during three-dimensional (3D) object viewing. Neurons in both streams encode 3D structure from binocular disparity, synchronized activity between parietal and inferotemporal areas is present during 3D structure categorization, and clusters of 3D structure-selective neurons in parietal cortex are anatomically connected to ventral stream areas. In addition, caudal intraparietal cortex exerts a causal influence on 3D-structure related activations in more anterior parietal cortex and in inferotemporal cortex. Thus, both anatomical and functional evidence indicates that the dorsal and the ventral visual stream interact during 3D object viewing.

Analysis of haptic information in the cerebral cortex

Haptic sensing of objects acquires information about a number of properties. This review summarizes current understanding about how these properties are processed in the cerebral cortex of macaques and humans. Nonnoxious somatosensory inputs, after initial processing in primary somatosensory cortex, are partially segregated into different pathways. A ventrally directed pathway carries information about surface texture into parietal opercular cortex and thence to medial occipital cortex. A dorsally directed pathway transmits information regarding the location of features on objects to the intraparietal sulcus and frontal eye fields. Shape processing occurs mainly in the intraparietal sulcus and lateral occipital complex, while orientation processing is distributed across primary somatosensory cortex, the parietal operculum, the anterior intraparietal sulcus, and a parieto-occipital region. For each of these properties, the respective areas outside primary somatosensory cortex also process corresponding visual information and are thus multisensory. Consistent with the distributed neural processing of haptic object properties, tactile spatial acuity depends on interaction between bottom-up tactile inputs and top-down attentional signals in a distributed neural network. Future work should clarify the roles of the various brain regions and how they interact at the network level.

Neuroimaging Evidence for 2 Types of Plasticity in Association with Visual Perceptual Learning

Visual perceptual learning (VPL) is long-term performance improvement as a result of perceptual experience. It is unclear whether VPL is associated with refinement in representations of the trained feature (feature-based plasticity), improvement in processing of the trained task (task-based plasticity), or both. Here, we provide empirical evidence that VPL of motion detection is associated with both types of plasticity which occur predominantly in different brain areas. Before and after training on a motion detection task, subjects' neural responses to the trained motion stimuli were measured using functional magnetic resonance imaging. In V3A, significant response changes after training were observed specifically to the trained motion stimulus but independently of whether subjects performed the trained task. This suggests that the response changes in V3A represent feature-based plasticity in VPL of motion detection. In V1 and the intraparietal sulcus, significant response changes were found only when subjects performed the trained task on the trained motion stimulus. This suggests that the response changes in these areas reflect task-based plasticity. These results collectively suggest that VPL of motion detection is associated with the 2 types of plasticity, which occur in different areas and therefore have separate mechanisms at least to some degree.

Posterior Parietal Cortex Drives Inferotemporal Activations During Three-Dimensional Object Vision

The primate visual system consists of a ventral stream, specialized for object recognition, and a dorsal visual stream, which is crucial for spatial vision and actions. However, little is known about the interactions and information flow between these two streams. We investigated these interactions within the network processing three-dimensional (3D) object information, comprising both the dorsal and ventral stream. Reversible inactivation of the macaque caudal intraparietal area (CIP) during functional magnetic resonance imaging (fMRI) reduced fMRI activations in posterior parietal cortex in the dorsal stream and, surprisingly, also in the inferotemporal cortex (ITC) in the ventral visual stream. Moreover, CIP inactivation caused a perceptual deficit in a depth-structure categorization task. CIP-microstimulation during fMRI further suggests that CIP projects via posterior parietal areas to the ITC in the ventral stream. To our knowledge, these results provide the first causal evidence for the flow of visual 3D information from the dorsal stream to the ventral stream, and identify CIP as a key area for depth-structure processing. Thus, combining reversible inactivation and electrical microstimulation during fMRI provides a detailed view of the functional interactions between the two visual processing streams.

Morphological patterns of the intraparietal sulcus and the anterior intermediate parietal sulcus of Jensen in the human brain

Distinct parts of the intraparietal sulcal cortex contribute to sensorimotor integration and visual spatial attentional processing. A detailed examination of the morphological relations of the different segments of the complex intraparietal sulcal region in the human brain in standard stereotaxic space, which is a prerequisite for detailed structure-to-function studies, is not available. This study examined the intraparietal sulcus (IPS) and the related sulcus of Jensen in magnetic resonance imaging brain volumes registered in the Montreal Neurological Institute stereotaxic space. It was demonstrated that the IPS is divided into two branches: the anterior ramus and the posterior ramus of the IPS, often separated by a submerged gyral passage. The sulcus of Jensen emerges between the anterior and posterior rami of the IPS, and its ventral end is positioned between the first and second caudal branches of the superior temporal sulcus. In a small number of brains, the sulcus of Jensen may merge superficially with the first caudal branch of the superior temporal sulcus. The above morphological findings are discussed in relation to previously reported functional neuroimaging findings and provide the basis for future exploration of structure-to-function relations in the posterior parietal region of individual subjects.

Cortical Connections of the Caudal Portion of Posterior Parietal Cortex in Prosimian Galagos

Posterior parietal cortex (PPC) of prosimian galagos includes a rostral portion (PPCr) where electrical stimulation evokes different classes of complex movements from different subregions, and a caudal portion (PPCc) where such stimulation fails to evoke movements in anesthetized preparations ( Stepniewska, Fang et al. 2009). We placed tracer injections into PPCc to reveal patterns of its cortical connections. There were widespread connections within PPCc as well as connections with PPCr and extrastriate visual areas, including V2 and V3. Weaker connections were with dorsal premotor cortex, and the frontal eye field. The connections of different parts of PPCc with visual areas were roughly retinotopic such that injections to dorsal PPCc labeled more neurons in the dorsal portions of visual areas, representing lower visual quadrant, and injections to ventral PPCc labeled more neurons in ventral portions of these visual areas, representing the upper visual quadrant. We conclude that much of the PPCc contains a crude representation of the contralateral visual hemifield, with inputs largely, but not exclusively, from higher-order visual areas that are considered part of the dorsal visuomotor processing stream. As in galagos, the caudal half of PPC was likely visual in early primates, with the rostral PPC half mediating sensorimotor functions.

Dynamic Parieto-premotor Network for Mental Image Transformation Revealed by Simultaneous EEG and fMRI Measurement

Previous studies have suggested that the posterior parietal cortices and premotor areas are involved in mental image transformation. However, it remains unknown whether these regions really cooperate to realize mental image transformation. In this study, simultaneous EEG and fMRI were performed to clarify the spatio-temporal properties of neural networks engaged in mental image transformation. We adopted a modified version of the mental clock task used by Sack et al. [Sack, A. T., Camprodon, J. A., Pascual-Leone, A., & Goebel, R. The dynamics of interhemispheric compensatory processes in mental imagery. Science, 308, 702–704, 2005; Sack, A. T., Sperling, J. M., Prvulovic, D., Formisano, E., Goebel, R., Di Salle, F., et al. Tracking the mind's image in the brain II: Transcranial magnetic stimulation reveals parietal asymmetry in visuospatial imagery. Neuron, 35, 195–204, 2002]. In the modified mental clock task, participants mentally rotated clock hands from the position initially presented at a learned speed for various durations. Subsequently, they matched the position to the visually presented clock hands. During mental rotation of the clock hands, we observed significant beta EEG suppression with respect to the amount of mental rotation at the right parietal electrode. The beta EEG suppression accompanied activity in the bilateral parietal cortices and left premotor cortex, representing a dynamic cortical network for mental image transformation. These results suggest that motor signals from the premotor area were utilized for mental image transformation in the parietal areas and for updating the imagined clock hands represented in the right posterior parietal cortex.

Two action systems in the human brain

The distinction between dorsal and ventral visual processing streams, first proposed by Ungerleider and Mishkin (1982) and later refined by Milner and Goodale (1995) has been elaborated substantially in recent years, spurred by two developments. The first was proposed in large part by Rizzolatti and Matelli (2003) and is a more detailed description of the multiple neural circuits connecting the frontal, temporal, and parietal cortices. Secondly, there are a number of behavioral observations that the classic "two visual systems" hypothesis is unable to accommodate without additional assumptions. The notion that the Dorsal stream is specialized for "where" or "how" actions and the Ventral stream for "What" knowledge cannot account for two prominent disorders of action, limb apraxia and optic ataxia, that represent a double dissociation in terms of the types of actions that are preserved and impaired. A growing body of evidence, instead, suggests that there are at least two distinct Dorsal routes in the human brain, referred to as the "Grasp" and "Use" systems. Both of these may be differentiated from the Ventral route in terms of neuroanatomic localization, representational specificity, and time course of information processing.

Neural changes with tactile learning reflect decision-level reweighting of perceptual readout

Despite considerable work, the neural basis of perceptual learning remains uncertain. For visual learning, although some studies suggested that changes in early sensory representations are responsible, other studies point to decision-level reweighting of perceptual readout. These competing possibilities have not been examined in other sensory systems, investigating which could help resolve the issue. Here we report a study of human tactile microspatial learning in which participants achieved >six-fold decline in acuity threshold after multiple training sessions. Functional magnetic resonance imaging was performed during performance of the tactile microspatial task and a control, tactile temporal task. Effective connectivity between relevant brain regions was estimated using multivariate, autoregressive models of hidden neuronal variables obtained by deconvolution of the hemodynamic response. Training-specific increases in task-selective activation assessed using the task × session interaction and associated changes in effective connectivity primarily involved subcortical and anterior neocortical regions implicated in motor and/or decision processes, rather than somatosensory cortical regions. A control group of participants tested twice, without intervening training, exhibited neither threshold improvement nor increases in task-selective activation. Our observations argue that neuroplasticity mediating perceptual learning occurs at the stage of perceptual readout by decision networks. This is consonant with the growing shift away from strictly modular conceptualization of the brain toward the idea that complex network interactions underlie even simple tasks. The convergence of our findings on tactile learning with recent studies of visual learning reconciles earlier discrepancies in the literature on perceptual learning.

Integration of texture and disparity cues to surface slant in dorsal visual cortex

Reliable estimation of three-dimensional (3D) surface orientation is critical for recognizing and interacting with complex 3D objects in our environment. Human observers maximize the reliability of their estimates of surface slant by integrating multiple depth cues. Texture and binocular disparity are two such cues, but they are qualitatively very different. Existing evidence suggests that representations of surface tilt from each of these cues coincide at the single-neuron level in higher cortical areas. However, the cortical circuits responsible for 1) integration of such qualitatively distinct cues and 2) encoding the slant component of surface orientation have not been assessed. We tested for cortical responses related to slanted plane stimuli that were defined independently by texture, disparity, and combinations of these two cues. We analyzed the discriminability of functional MRI responses to two slant angles using multivariate pattern classification. Responses in visual area V3B/KO to stimuli containing congruent cues were more discriminable than those elicited by single cues, in line with predictions based on the fusion of slant estimates from component cues. This improvement was specific to congruent combinations of cues: incongruent cues yielded lower decoding accuracies, which suggests the robust use of individual cues in cases of large cue conflicts. These data suggest that area V3B/KO is intricately involved in the integration of qualitatively dissimilar depth cues.

The representation of tool and non-tool object information in the human intraparietal sulcus

Humans have an amazing ability to quickly and efficiently recognize and interact with visual objects in their environment. The underlying neural processes supporting this ability have been mainly explored in the ventral visual stream. However, the dorsal stream has been proposed to play a critical role in guiding object-directed actions. This hypothesis is supported by recent neuroimaging studies that have identified object-selective and tool-related activity in human parietal cortex. In the present study, we sought to delineate tool-related information in the anterior portions of the human intraparietal sulcus (IPS) and relate it to recently identified motor-defined and topographic regions of interest (ROIs) using functional MRI in individual subjects. Consistent with previous reports, viewing pictures of tools compared with pictures of animals led to a higher blood oxygenation level-dependent (BOLD) response in the left anterior IPS. For every subject, this activation was located lateral, anterior, and inferior to topographic area IPS5 and lateral and inferior to a motor-defined human parietal grasp region (hPGR). In a separate experiment, subjects viewed pictures of tools, animals, graspable (non-tool) objects, and scrambled objects. An ROI-based time-course analysis showed that tools evoked a stronger BOLD response than animals throughout topographic regions of the left IPS. Additionally, graspable objects evoked stronger responses than animals, equal to responses to tools, in posterior regions and weaker responses than tools, equal to responses to animals, in anterior regions. Thus the left anterior tool-specific region may integrate visual information encoding graspable features of objects from more posterior portions of the IPS with experiential knowledge of object use and function to guide actions.

Functional organization of human posterior parietal cortex: grasping- and reaching-related activations relative to topographically organized cortex

The act of reaching to grasp an object requires the coordination between transporting the arm and shaping the hand. Neurophysiological, neuroimaging, neuroanatomic, and neuropsychological studies in macaque monkeys and humans suggest that the neural networks underlying grasping and reaching acts are at least partially separable within the posterior parietal cortex (PPC). To better understand how these neural networks have evolved in primates, we characterized the relationship between grasping- and reaching-related responses and topographically organized areas of the human intraparietal sulcus (IPS) using functional MRI. Grasping-specific activation was localized to the left anterior IPS, partially overlapping with the most anterior topographic regions and extending into the postcentral sulcus. Reaching-specific activation was localized to the left precuneus and superior parietal lobule, partially overlapping with the medial aspects of the more posterior topographic regions. Although the majority of activity within the topographic regions of the IPS was nonspecific with respect to movement type, we found evidence for a functional gradient of specificity for reaching and grasping movements spanning posterior-medial to anterior-lateral PPC. In contrast to the macaque monkey, grasp- and reach-specific activations were largely located outside of the human IPS.

An fMRI study of reduced perceptual load-dependent modulation of task-irrelevant activity in adults with autism spectrum conditions

Recent studies on selective attention have demonstrated that the perceptual load of a task determines the processing stage at which irrelevant sensory stimuli are filtered out. Although individuals with autism spectrum conditions (ASC) have been repeatedly reported to display several kinds of abnormal behavior related to attention deficits, the neural mechanisms underlying these deficits have not been well investigated within the framework of the load dependency of selective attention. The present study used functional magnetic resonance imaging (fMRI) to examine the brain responses of adults with high-functioning ASC to irrelevant visual distractors while performing a visual target detection task under high or low perceptual load. We observed that the increased perceptual load activated regions of the fronto-parietal attention network of controls and ASC comparably. On the other hand, the visual cortex activity evoked by visual distractors was less modulated by the increased perceptual load in ASC than in controls. Simple regression analyses showed that the degree of the modulation was significantly correlated with the severity of the autistic symptoms. We also observed reduced load-dependent modulation of the functional connectivity between the intraparietal and visual regions in the ASC group. These results revealed neural correlates for abnormal perceptual load-dependent engagement of visual attention in ASC, which may underlie aspects of cognitive and behavioral characteristics of these disorders.

The role of finger representations and saccades for number processing: an FMRI study in children

A possible functional role of finger representations for the development of early numerical cognition has been the subject of recent debate; however, until now, only behavioral studies have directly supported this view. Working from recent models of number processing, we focused on the neural networks involved in numerical tasks and their relationship to the areas underlying finger representations and saccades in children aged 6–12 years. We were able to differentiate three parietal circuits that were related to distinct aspects of number processing. Abstract magnitude processing was subserved by an association area also activated by saccades and visually guided finger movements. Addition processes led to activation in an area only engaged during saccade encoding, whereas counting processes resulted in the activation of an area only activated during visually guided finger movements, namely in the anterior intraparietal sulcus. Apart from this area, a large network of specifically finger-related brain areas including the ventral precentral sulcus, supplementary motor area, dorso-lateral prefrontal cortex, insula, thalamus, midbrain, and cerebellum was activated during (particularly non-symbolic) exact addition but not during magnitude comparison. Moreover, a finger-related activation cluster in the right ventral precentral sulcus was only present during non-symbolic addition and magnitude comparison, but not during symbolic number processing tasks. We conclude that finger counting may critically mediate the step from non-symbolic to symbolic and exact number processing via somatosensory integration processes and therefore represents an important example of embodied cognition.

The extraction of 3D shape in the visual system of human and nonhuman primates

Depth structure, the third dimension of object shape, is extracted from disparity, motion, texture, and shading in the optic array. Gradient-selective neurons play a key role in this process. Such neurons occur in CIP, AIP, TEs, and F5 (for first- or second-order disparity gradients), in MT/V5, in FST (for speed gradients), and in CIP and TEs (for texture gradients). Most of these regions are activated during magnetic resonance scanning in alert monkeys by comparing 3D conditions with the 2D controls for the different cues. Similarities in activation patterns of monkeys and humans tested with identical paradigms suggest that like gradient-selective neurons are found in corresponding human cortical areas. This view gains credence as the homologies between such areas become more evident. Furthermore, 3D shape-processing networks are similar in the two species, with the exception of the greater involvement of human posterior parietal cortex in the extraction of 3D shape from motion. Thus we can begin to understand how depth structure is extracted from motion, disparity, and texture in the primate brain, but the extraction of depth structure from shading and that of wire-like objects requires further scrutiny.

The organization and evolution of dorsal stream multisensory motor pathways in primates

In Prosimian primates, New World monkeys, and Old World monkeys microstimulation with half second trains of electrical pulses identifies separate zones in posterior parietal cortex (PPC) where reaching, defensive, grasping, and other complex movements can be evoked. Each functional zone receives a different pattern of visual and somatosensory inputs, and projects preferentially to functionally matched parts of motor and premotor cortex. As PPC is a relatively small portion of cortex in most mammals, including the close relatives of primates, we suggest that a larger, more significant PPC emerged with the first primates as a region where several ethologically relevant behaviors could be initiated by sensory and intrinsic signals, and mediated via connections with premotor and motor cortex. While several classes of PPC modules appear to be retained by all primates, elaboration and differentiation of these modules likely occurred in some primates, especially humans.

Dual pathways for haptic and visual perception of spatial and texture information

Segregation of information flow along a dorsally directed pathway for processing object location and a ventrally directed pathway for processing object identity is well established in the visual and auditory systems, but is less clear in the somatosensory system. We hypothesized that segregation of location vs. identity information in touch would be evident if texture is the relevant property for stimulus identity, given the salience of texture for touch. Here, we used functional magnetic resonance imaging (fMRI) to investigate whether the pathways for haptic and visual processing of location and texture are segregated, and the extent of bisensory convergence. Haptic texture-selectivity was found in the parietal operculum and posterior visual cortex bilaterally, and in parts of left inferior frontal cortex. There was bisensory texture-selectivity at some of these sites in posterior visual and left inferior frontal cortex. Connectivity analyses demonstrated, in each modality, flow of information from unisensory non-selective areas to modality-specific texture-selective areas and further to bisensory texture-selective areas. Location-selectivity was mostly bisensory, occurring in dorsal areas, including the frontal eye fields and multiple regions around the intraparietal sulcus bilaterally. Many of these regions received input from unisensory areas in both modalities. Together with earlier studies, the activation and connectivity analyses of the present study establish that somatosensory processing flows into segregated pathways for location and object identity information. The location-selective somatosensory pathway converges with its visual counterpart in dorsal frontoparietal cortex, while the texture-selective somatosensory pathway runs through the parietal operculum before converging with its visual counterpart in visual and frontal cortex. Both segregation of sensory processing according to object property and multisensory convergence appear to be universal organizing principles.

Neural structures and mechanisms involved in scene recognition: a review and interpretation

Since the discovery in 1996 that a region within caudal parahippocampal cortex subserves learning and recall of topographical information, numerous studies aimed at elucidating the structures and pathways involved in scene recognition have been published. Neuroimaging studies, in particular, have revealed the locations and identities of some of the principal cortical structures that mediate these faculties. In the present study the detailed organization of the system is examined, based on a meta-analysis of neuroimaging studies of scene processing in human subjects, combined with reviews of the results of lesions on this type of processing, single neuron studies, and available hodological data in non-human primates. A cortical hierarchy of structures that mediate scene recognition is established based on these data, and an attempt is made to determine the function of the individual components of the system.

Morphological patterns of the postcentral sulcus in the human brain

The morphological structure of the postcentral sulcus and its variability were investigated in 40 structural magnetic resonance images of the human brain registered to the Montreal Neurological Institute (MNI) proportional stereotaxic space. This analysis showed that the postcentral sulcus is not a single sulcus, but rather a complex of sulcal segments separated by gyri, which merge their banks at distinct locations. Most of these gyri are submerged deep within the sulcus and can be observed only by examining the depth of the sulcus, although a small proportion may be observed from the surface of the brain. In the majority of the examined cerebral hemispheres (73.75%), the postcentral sulcus is separated into two or three segments or, less frequently, into four or five segments (12.5%), or it remains continuous (13.75%). Examination of the in-depth relationship between the postcentral sulcus and the intraparietal sulcus revealed that these two sulci may appear to join on the surface of the brain but they are in fact always separated by a gyrus in the cortical depth. In 32.5% of the examined hemispheres, a dorsoventrally oriented sulcus, the transverse postcentral sulcus, is located anterior to the postcentral sulcus on the lower part of the postcentral gyrus. Systematic examination of the morphology of the postcentral sulcus in the proportional stereotaxic space that is used in functional neuroimaging studies is the first step toward the establishment of anatomical-functional correlations in the anterior parietal lobe.

Perception of object motion in three-dimensional space induced by cast shadows

Cast shadows can be salient depth cues in three-dimensional (3D) vision. Using a motion illusion in which a ball is perceived to roll in depth on the bottom or to flow in the front plane depending on the slope of the trajectory of its cast shadow, we investigated cortical mechanisms underlying 3D vision based on cast shadows using fMRI techniques. When modified versions of the original illusion, in which the slope of the shadow trajectory (shadow slope) was changed in 5 steps from the same one as the ball trajectory to the horizontal, were presented to participants, their perceived ball trajectory shifted gradually from rolling on the bottom to floating in the front plane as the change of the shadow slope. This observation suggests that the perception of the ball trajectory in this illusion is strongly affected by the motion of the cast shadow. In the fMRI study, cortical activity during observation of the movies of the illusion was investigated. We found that the bilateral posterior-occipital sulcus (POS) and right ventral precuneus showed activation related to the perception of the ball trajectory induced by the cast shadows in the illusion. Of these areas, it was suggested that the right POS may be involved in the inferring of the ball trajectory by the given spatial relation between the ball and the shadow. Our present results suggest that the posterior portion of the medial parietal cortex may be involved in 3D vision by cast shadows.

Visuospatial perspective taking in a dynamic environment: perceiving moving objects from a first-person-perspective induces a disposition to act

Spatial perspective taking is an everyday cognitive process that is involved in predicting the outcome of goal directed behavior. We used dynamic virtual stimuli and fMRI to investigate at the neural level whether motion perception interacts with spatial perspective taking in a life-like design. Subjects were asked to perform right-left-decisions about the position of either a motionless, hovering (STATic) or a flying ball (DYNamic), either from their own (1PP) or from the perspective of a virtual character (avatar, 3PP). Our results showed a significant interaction of STIMULUS TYPE and PERSPECTIVE with significantly increased activation in right posterior intraparietal sulcus (IPS) for 1PPDYN condition. As the IPS is critically involved in the computation of object-directed action preparation, we suppose that the simple perception of potentially action-relevant dynamic objects induces a 'readiness for (re)action', restricted to the 1PP. Results are discussed against the background of current theories on embodiment and enactive perception.

Cross-modal plasticity of tactile perception in blindness

This review focusses on cross-modal plasticity resulting from visual deprivation. This is viewed against the background of task-specific visual cortical recruitment that is routine during tactile tasks in the sighted and that may depend in part on visual imagery. Superior tactile perceptual performance in the blind may be practice-related, although there are unresolved questions regarding the effects of Braille-reading experience and the age of onset of blindness. While visual cortical areas are clearly more involved in tactile microspatial processing in the blind than in the sighted, it still remains unclear how to reconcile these tactile processes with the growing literature implicating visual cortical activity in a wide range of cognitive tasks in the blind, including those involving language, or with studies of short-term, reversible visual deprivation in the normally sighted that reveal plastic changes even over periods of hours or days.

Object familiarity modulates the relationship between visual object imagery and haptic shape perception

Although visual cortical engagement in haptic shape perception is well established, its relationship with visual imagery remains controversial. We addressed this using functional magnetic resonance imaging during separate visual object imagery and haptic shape perception tasks. Two experiments were conducted. In the first experiment, the haptic shape task employed unfamiliar, meaningless objects, whereas familiar objects were used in the second experiment. The activations evoked by visual object imagery overlapped more extensively, and their magnitudes were more correlated, with those evoked during haptic shape perception of familiar, compared to unfamiliar, objects. In the companion paper (Deshpande et al., this issue), we used task-specific functional and effective connectivity analyses to provide convergent evidence: these analyses showed that the neural networks underlying visual imagery were similar to those underlying haptic shape perception of familiar, but not unfamiliar, objects. We conclude that visual object imagery is more closely linked to haptic shape perception when objects are familiar, compared to when they are unfamiliar.

Visual-manual exploration and posterior parietal cortex in humans

Areas of human posterior parietal cortex (PPC) specialized for processing sensorimotor information associated with visually locating an object, reaching to grasp, and manually exploring that object were examined using functional MRI. Cortical activation was observed in response to three tasks: 1) saccadic eye movements, 2) visually guided reaching to grasp, and 3) manual shape discrimination. During saccadic eye movements, cortical fields within the lateral and rostral superior parietal lobe (SPL) and the caudal SPL and parieto-occipital boundary were active. During visually guided reaching to grasp, regions of cortex within the postcentral sulcus (PoCS) and rostral intraparietal sulcus (IPS) were active, as well as the caudal SPL of the left hemisphere and the medial and caudal IPS of the right hemisphere. Cortical regions at the junction of the IPS and PoCS and an area in the medial SPL were active bilaterally during shape manipulation. Only a few regions were most active during a single motor behavior, whereas several areas were highly active during two or more tasks. Hemispheric asymmetries in activation patterns were observed during visually guided reaching to grasp. The gross areal organization of human PPC is likely similar to the pattern previously described in nonhuman primates, including multifunctional regions and asymmetric processing of some manual abilities.

I know where you'll look: an fMRI study of oculomotor intention and a change of motor plan

Background

Electrophysiological studies in monkeys showed that the intention to perform a saccade and the covert change in motor plan are reflected in the neural activity of the posterior parietal cortex (PPC).

Methods

To investigate whether such covert intentional processes are demonstrable in humans as well we used event related functional MRI. Subjects were instructed to fixate a central target, which changed its color in order to indicate the direction of a subsequent saccade. Unexpectedly for the subjects, the color changed again in half of the trials to instruct a spatially opposite saccade.

Results

The double-cue induced synergistic and prolonged signals in early visual areas, the motion specific visual area V5, PPC, and the supplementary and frontal eye field. At the single subject level it became evident that the PPC split up in two separate subareas. In the posterior region, the signal change correlated with the change in motor plan: activation strongly decreased when the cue instructed an ipsiversive saccade while it strongly increased when it instructed a contraversive saccade. In the anterior region, the signal change was motor related irrespective of the spatial direction of the upcoming saccade.

Conclusion

Thus, the human PPC holds at least two different areas for planning and executing saccadic eye movements.

Context-specific grasp movement representation in the macaque anterior intraparietal area

To perform grasping movements, the hand is shaped according to the form of the target object and the intended manipulation, which in turn depends on the context of the action. The anterior intraparietal cortex (AIP) is strongly involved in the sensorimotor transformation of grasping movements, but the extent to which it encodes context-specific information for hand grasping is unclear. To explore this issue, we recorded 571 single-units in AIP of two macaques during a delayed grasping task, in which animals were instructed by an external context cue (LED) to perform power or precision grips on a handle that was presented in various orientations. While 55% of the recorded neurons encoded the object orientation from the cue epoch on, the number of cells encoding the grip type increased from 25% during the cue epoch to 58% during movement execution. Furthermore, a classification of cells according to the time of their tuning onset revealed differences in the function and anatomical location of early- versus late-tuned cells. In a cue separation task, when the object was presented first, neurons representing power or precision grips were activated simultaneously until the actual grip type was instructed. In contrast, when the grasp type instruction was presented before the object, type information was only weakly represented in AIP, but was strongly encoded after the grasp target was revealed. We conclude that AIP encodes context specific hand grasping movements to perceived objects, but in the absence of a grasp target, the encoding of context information is weak.

A putative model of multisensory object representation

This review surveys the recent literature on visuo-haptic convergence in the perception of object form, with particular reference to the lateral occipital complex (LOC) and the intraparietal sulcus (IPS) and discusses how visual imagery or multisensory representations might underlie this convergence. Drawing on a recent distinction between object- and spatially-based visual imagery, we propose a putative model in which LOtv, a subregion of LOC, contains a modality-independent representation of geometric shape that can be accessed either bottom-up from direct sensory inputs or top-down from frontoparietal regions. We suggest that such access is modulated by object familiarity: spatial imagery may be more important for unfamiliar objects and involve IPS foci in facilitating somatosensory inputs to the LOC; by contrast, object imagery may be more critical for familiar objects, being reflected in prefrontal drive to the LOC.

Parietal regions processing visual 3D shape extracted from disparity

Three-dimensional (3D) shape is important for the visual control of grasping and manipulation. We used fMRI to study the processing of 3D shape extracted from disparity in human parietal cortex. Subjects stereoscopically viewed random-line stimuli portraying a 3D structure, a 2D structure in multiple depth planes or a 2D structure in the fixation plane. Subtracting the second from the first condition yields depth-structure sensitive regions and subtracting the third from the second position-in-depth sensitive regions. Two anterior intraparietal sulcus (IPS) regions, the dorsal IPS medial (DIPSM) and the dorsal IPS anterior (DIPSA) regions, were sensitive to depth structure and not to position in depth, while a posterior IPS region, the ventral IPS (VIPS) region, had a mixed sensitivity. All three IPS regions were also sensitive to 2D shape, indicating that they carry full 3D shape information. Finally DIPSM, but not DIPSA was sensitive to a saccade-related task. These results underscore the importance of anterior IPS regions in the processing of 3D shape, in agreement with their proximity to grasping-related regions. Moreover, comparison with the results of Durand, J.B., Nelissen, K., Joly, O., Wardak, C., Todd, J.T., Norman, J.F., Janssen, P., Vanduffel, W., Orban, G.A., 2007. Anterior Regions of Monkey Parietal Cortex Process Visual 3D Shape. Neuron 55, 493-505 obtained in the monkey indicates that DIPSA and DIPSM may represent human homologues for the posterior part of AIP and the adjoining part of LIP respectively.

Cortical mechanisms of retinal and extraretinal smooth pursuit eye movements to different target velocities

Smooth pursuit eye movements (SPEM) are used to maintain focus upon moving targets. The generation of SPEM velocity is controlled by retinal information and extraretinal signals. Although there is a wealth of studies investigating retinal and extraretinal SPEM control, the main questions regarding the cortical mechanisms involved in the processing of SPEM to different stimulus velocities are still unresolved. We applied an innovative event-related fMRI-design by presenting target ramps at different velocities (5, 10, 15, 20 degrees/s) with both continuous target presentation and intervals of target blanking. The stimulus parameters were integrated into the statistical model and eye movements were registered to confirm SPEM performance. Our results clearly demonstrate that in humans the oculomotor network (V5, frontal and supplementary eye fields, lateral intraparietal area) is engaged in the processing of retinal and extraretinal SPEM velocity. Within this network neural activity increases with increasing target velocity. During extraretinal SPEM, additional engagement of the dorsolateral prefrontal cortex, angular gyrus, parahippocampal gyrus and superior temporal gyrus occurs. These regions encode cognitive functions such as memory, attention and monitoring. The activation of the inferior parietal cortex seems to be related to the interaction between velocity and blanking thereby underlining its relevance for task switching and sensorimotor transformation.