Human Ventral Temporal Cortex Research Articles

Neural representations of faces and limbs neighbor in human high-level visual cortex: evidence for a new organization principle

Neurophysiology and optical imaging studies in monkeys and functional magnetic resonance imaging (fMRI) studies in both monkeys and humans have localized clustered neural responses in inferotemporal cortex selective for images of biologically relevant categories, such as faces and limbs. Using higher resolution (1.5 mm voxels) fMRI scanning methods than past studies (3–5 mm voxels), we recently reported a network of multiple face- and limb-selective regions that neighbor one another in human ventral temporal cortex (Weiner and Grill-Spector, Neuroimage, 52(4):1559–1573, 2010) and lateral occipitotemporal cortex (Weiner and Grill-Spector, Neuroimage, 56(4):2183–2199, 2011). Here, we expand on three basic organization principles of high-level visual cortex revealed by these findings: (1) consistency in the anatomical location of functional regions, (2) preserved spatial relationship among functional regions, and (3) a topographic organization of face- and limb-selective regions in adjacent and alternating clusters. We highlight the implications of this structure in comparing functional brain organization between typical and atypical populations. We conclude with a new model of high-level visual cortex consisting of ventral, lateral, and dorsal components, where multimodal processing related to vision, action, haptics, and language converges in the lateral pathway.Electronic supplementary materialThe online version of this article (doi:10.1007/s00426-011-0392-x) contains supplementary material, which is available to authorized users.

A Common, High-Dimensional Model of the Representational Space in Human Ventral Temporal Cortex

We present a high-dimensional model of the representational space in human ventral temporal (VT) cortex in which dimensions are response-tuning functions that are common across individuals and patterns of response are modeled as weighted sums of basis patterns associated with these response tunings. We map response-pattern vectors, measured with fMRI, from individual subjects' voxel spaces into this common model space using a new method, "hyperalignment." Hyperalignment parameters based on responses during one experiment--movie viewing--identified 35 common response-tuning functions that captured fine-grained distinctions among a wide range of stimuli in the movie and in two category perception experiments. Between-subject classification (BSC, multivariate pattern classification based on other subjects' data) of response-pattern vectors in common model space greatly exceeded BSC of anatomically aligned responses and matched within-subject classification. Results indicate that population codes for complex visual stimuli in VT cortex are based on response-tuning functions that are common across individuals.

Sparsely-distributed organization of face and limb activations in human ventral temporal cortex

Functional magnetic resonance imaging (fMRI) has identified face- and body part-selective regions, as well as distributed activation patterns for object categories across human ventral temporal cortex (VTC), eliciting a debate regarding functional organization in VTC and neural coding of object categories. Using high-resolution fMRI, we illustrate that face- and limb-selective activations alternate in a series of largely nonoverlapping clusters in lateral VTC along the inferior occipital gyrus (IOG), fusiform gyrus (FG), and occipito-temporal sulcus (OTS). Both general linear model (GLM) and multivoxel pattern (MVP) analyses show that face- and limb-selective activations minimally overlap and that this organization is consistent across experiments and days. We provide a reliable method to separate two face-selective clusters on the middle and posterior FG (mFus and pFus), and another on the IOG using their spatial relation to limb-selective activations and retinotopic areas hV4, VO-1/2, and hMT+. Furthermore, these activations show a gradient of increasing face selectivity and decreasing limb selectivity from the IOG to the mFus. Finally, MVP analyses indicate that there is differential information for faces in lateral VTC (containing weakly- and highly-selective voxels) relative to non-selective voxels in medial VTC. These findings suggest a sparsely-distributed organization where sparseness refers to the presence of several face- and limb-selective clusters in VTC, and distributed refers to the presence of different amounts of information in highly-, weakly-, and non-selective voxels. Consequently, theories of object recognition should consider the functional and spatial constraints of neural coding across a series of minimally overlapping category-selective clusters that are themselves distributed.

FMRI-adaptation and category selectivity in human ventral temporal cortex: regional differences across time scales.

Repeating object images produces stimulus-specific repetition suppression referred to as functional magnetic resonance imaging-adaptation (fMRI-A) in ventral temporal cortex (VTC). However, the effects of stimulus repetition on functional selectivity are largely unknown. We investigated the effects of short-lagged (SL, immediate) and long-lagged (LL, many intervening stimuli) repetitions on category selectivity in VTC using high-resolution fMRI. We asked whether repetition produces scaling or sharpening of fMRI responses both within category-selective regions as well as in the distributed response pattern across VTC. Results illustrate that repetition effects across time scales vary quantitatively along an anterior-posterior axis and qualitatively along a lateral-medial axis. In lateral VTC, both SL and LL repetitions produce proportional fMRI-A with no change in either selectivity or distributed responses as predicted by a scaling model. Further, there is larger fMRI-A in anterior subregions irrespective of category selectivity. Medial VTC exhibits similar scaling effects during SL repetitions. However, for LL repetitions, both the selectivity and distributed pattern of responses vary with category in medial VTC as predicted by a sharpening model. Specifically, there is larger fMRI-A for nonpreferred categories compared with the preferred category, and category selectivity does not predict fMRI-A across the pattern of distributed response. Finally, simulations indicate that different neural mechanisms likely underlie fMRI-A in medial compared to lateral VTC. These results have important implications for future fMRI-A experiments because they suggest that fMRI-A does not reflect a universal neural mechanism and that results of fMRI-A experiments will likely be paradigm independent in lateral VTC but paradigm dependent in medial VTC.

FMRI-Adaptation and category selectivity in human ventral temporal cortex: Evidence for the scaling and sharpening models

fMRI-Adaptation and category selectivity in human ventral temporal cortex: Evidence for the scaling and sharpening models

Neural Representations of Faces and Body Parts in Macaque and Human Cortex: A Comparative fMRI Study

Single-cell studies in the macaque have reported selective neural responses evoked by visual presentations of faces and bodies. Consistent with these findings, functional magnetic resonance imaging studies in humans and monkeys indicate that regions in temporal cortex respond preferentially to faces and bodies. However, it is not clear how these areas correspond across the two species. Here, we directly compared category-selective areas in macaques and humans using virtually identical techniques. In the macaque, several face- and body part-selective areas were found located along the superior temporal sulcus (STS) and middle temporal gyrus (MTG). In the human, similar to previous studies, face-selective areas were found in ventral occipital and temporal cortex and an additional face-selective area was found in the anterior temporal cortex. Face-selective areas were also found in lateral temporal cortex, including the previously reported posterior STS area. Body part-selective areas were identified in the human fusiform gyrus and lateral occipitotemporal cortex. In a first experiment, both monkey and human subjects were presented with pictures of faces, body parts, foods, scenes, and man-made objects, to examine the response profiles of each category-selective area to the five stimulus types. In a second experiment, face processing was examined by presenting upright and inverted faces. By comparing the responses and spatial relationships of the areas, we propose potential correspondences across species. Adjacent and overlapping areas in the macaque anterior STS/MTG responded strongly to both faces and body parts, similar to areas in the human fusiform gyrus and posterior STS. Furthermore, face-selective areas on the ventral bank of the STS/MTG discriminated both upright and inverted faces from objects, similar to areas in the human ventral temporal cortex. Overall, our findings demonstrate commonalities and differences in the wide-scale brain organization between the two species and provide an initial step toward establishing functionally homologous category-selective areas.

Perception Matches Selectivity in the Human Anterior Color Center

Human ventral cortex contains at least two visual areas selective for color [1]: a posterior center in the lingual gyrus labeled V4 [2-4], V8 [5], or VO-1 [6] and an anterior center in the medial fusiform that has been labeled V4alpha[3, 4]. We examined the properties of the anterior color center using electrical recording and electrical stimulation in a subject with an electrode implanted over the anterior color center, as determined with BOLD fMRI in the same subject. Presentation of visual stimuli evoked local field potentials from the electrode. Consistent with fMRI, the potentials were larger for chromatic than achromatic stimuli. The potentials differed depending on stimulus color, with blue-purple colors evoking the largest response. The spatial receptive field of the electrode was central/parafoveal with a contralateral bias. In the absence of a visual stimulus, electrical stimulation of the electrode produced an artificial visual percept of a blue-purple color near the center of gaze. These results provide direct evidence of a tight link between selectivity and perception in ventral temporal cortex. Electrical stimulation of the anterior color center is sufficient to produce the conscious percept of a color whose identity is determined by the selectivity of the stimulated neurons.