Biology subjects

Grill-Spector, K.

Publications and source records attributed to Grill-Spector, K..

29 records · Page 2Linked to original sources

bioRxiv2020

Differential spatial processing in ventral and lateral face-selective regions is scaffolded by structural connections

Face-processing occurs across ventral and lateral visual streams, which are involved in static and dynamic face perception, respectively. However, the nature of spatial computations across streams is unknown. Using functional MRI and novel population receptive field (pRF) mapping, we measured pRFs in face-selective regions. Results reveal that spatial computations by pRFs in ventral face-selective regions are concentrated around the center of gaze (fovea), but spatial computations in lateral face-selective regions extend peripherally. Diffusion MRI reveals that these differences are mirrored by a preponderance of white matter connections between ventral face-selective regions and foveal early visual cortex (EVC), while connections with lateral regions are distributed more uniformly across EVC eccentricities. These findings suggest a rethinking of spatial computations in face-selective regions, showing that they vary across ventral and lateral streams, and further propose that spatial computations in high-level regions are scaffolded by the fine-grain pattern of white matter connections from EVC.

neuroscience↗

bioRxiv2020

Sulcal depth in medial ventral temporal cortex predicts the location of a place-selective region in macaques, children, and adults.

The evolution and development of anatomical-functional relationships in the cerebral cortex is of major interest in neuroscience. Here, we leveraged the fact that a functional region selective for visual scenes is located within a sulcus in medial ventral temporal cortex (VTC) in both humans and macaques to examine the relationship between sulcal depth and place-selectivity in medial VTC across species and age groups. To do so, we acquired anatomical and functional magnetic resonance imaging scans in 9 macaques, 26 human children, and 28 human adults. Our results revealed a strong structural-functional coupling between sulcal depth and place-selectivity across age groups and species in which selectivity was strongest at the deepest sulcal point (the sulcal pit). Interestingly, this coupling between sulcal depth and place-selectivity strengthens from childhood to adulthood in humans. Morphological analyses suggest that the stabilization of sulcal-functional coupling in adulthood may be due to sulcal deepening and areal expansion with age as well as developmental differences in cortical curvature at the pial, but not the white matter surfaces. Our results implicate sulcal features as functional landmarks in high-level visual cortex and highlight that sulcal-functional relationships in medial VTC are preserved between macaques and humans despite differences in cortical folding.

neuroscience↗

bioRxiv2019

Diverse temporal dynamics of repetition suppression revealed by intracranial recordings in human ventral temporal cortex

Repeated stimulus presentations commonly produce decreased neural responses - a phenomenon known as repetition suppression (RS) or adaptation - in ventral temporal cortex (VTC) in humans and nonhuman primates. However, the temporal features of RS in human VTC are not well understood. To fill this gap in knowledge, we utilized the precise spatial localization and high temporal resolution of electrocorticography (ECoG) from 9 human subjects implanted with intracranial electrodes in VTC. Subjects viewed non-repeated and repeated images of faces with long-lagged intervals and many intervening stimuli between repeats. We report three main findings: (i) robust RS occurs in VTC for activity in high-frequency broadband (HFB), but not lower frequency bands, (ii) RS of the HFB signal is associated with lower peak magnitude, lower total responses, and earlier peak responses, and (iii) RS effects occur early within initial stages of stimulus processing and persist for the entire stimulus duration. We discuss these findings in the context of early and late components of visual perception, as well as theoretical models of repetition suppression.

neuroscience↗

bioRxiv2018

Modeling neural tuning in human ventral temporal cortex predicts the perception of visual ambiguity

We have an amazing ability to categorize objects in the world around us. Nevertheless, how cortical regions in human ventral temporal cortex (VTC), which is critical for categorization, support this behavioral ability, is largely unknown. Here, we examined the relationship between neural responses and behavioral performance during the categorization of morphed silhouettes of faces and hands, which are animate categories processed in cortically adjacent regions in VTC. Our results reveal that the combination of neural responses from VTC face- and body-selective regions more accurately explains behavioral categorization than neural responses from either region alone. Furthermore, we built a model that predicts a persons behavioral performance using estimated parameters of brain-behavioral relationships from a different group of people. We further show that this brain-behavioral model generalizes to adjacent face- and body-selective regions in lateral occipito-temporal cortex. Thus, while face- and body-selective regions are located within functionally-distinct domain-specific networks, cortically adjacent regions from both networks likely integrate neural responses to resolve competing and perceptually ambiguous information from both categories.

neuroscience↗

bioRxiv2018

Separate lanes for math and reading in the white matter highways of the human brain

Math and reading involve distributed brain networks and learning disabilities associated with these skills have a high rate of co-occurrence. However, it is unknown what are shared vs. dissociated white matter substrates of math and reading networks. Here we address this question using an innovative, multimodal approach applying functional MRI, diffusion MRI, and quantitative MRI to define these networks and evaluate structural properties of their fascicles. Results reveal that the superior longitudinal (SLF) and arcuate (AF) fascicles are shared between math and reading networks. Strikingly, within these fascicles, reading- and math-related tracts are segregated into parallel sub-bundles and show structural differences related to myelination. These novel findings: (i) open a new avenue of research enabling linkage of sub-bundles within fascicles to behavior and (ii) may explain both isolated and comorbid cases of math and reading disabilities, which may be associated with white matter abnormalities within sub-bundles or entire fascicles, respectively.

neuroscience↗

bioRxiv2018

Novel childhood experience suggests eccentricity drives organization of human visual cortex

The functional organization of human high-level visual cortex, such as face and place-selective regions, is strikingly consistent across individuals. A fundamental, unanswered question in neuroscience is what dimensions of visual information constrain the development and topography of this shared brain organization? To answer this question, we scanned with fMRI a unique group of adults who, as children, engaged in extensive experience with a novel stimulus-Pokemon-which are dissimilar from other ecological categories such as faces and places along critical dimensions (foveal bias, rectilinearity, size, animacy) from. We find that experienced adults not only demonstrate distinct and consistent distributed cortical responses to Pokemon, but their activations suggest that it is the experienced retinal eccentricity during childhood that predicts the locus of distributed responses to Pokemon in adulthood. These data advance our understanding about how childhood experience and functional constraints shape the functional organization of the human brain.

neuroscience↗

bioRxiv2018

Apparent thinning of visual cortex during childhood is associated with myelination, not pruning

Microstructural mechanisms underlying apparent cortical thinning during childhood development are unknown. Using functional, quantitative, and diffusion magnetic resonance imaging in children and adults, we tested if tissue growth (lower T1 relaxation time and mean diffusivity (MD)) or pruning (higher T1 and MD) underlies cortical thinning in ventral temporal cortex (VTC). After age 5, T1 and MD decreased in mid and deep cortex of functionally-defined regions in lateral VTC, and in their adjacent white matter. T1 and MD decreases were (i) consistent with tissue growth related to myelin proliferation, which we verified with adult postmortem histology and (ii) correlated with apparent cortical thinning. Thus, contrary to prevailing theories, cortical tissue does not thin during childhood, it becomes more myelinated, shifting the gray-white matter boundary deeper into cortex. As tissue growth is prominent in regions with protracted functional development, our data suggest an intriguing hypothesis that functional development and myelination are interlinked.

neuroscience↗

bioRxiv2018

Differential Sustained and Transient Temporal Processing Across Visual Streams

How do high-level visual regions process the temporal aspects of our visual experience? While the temporal sensitivity of early visual cortex has been studied with fMRI in humans, temporal processing in high-level visual cortex is largely unknown. By modeling neural responses with millisecond precision in separate sustained and transient channels, and introducing a flexible encoding framework that captures differences in neural temporal integration time windows and response nonlinearities, we predict fMRI responses across visual cortex for stimuli ranging from 33 ms to 20 s. Using this innovative approach, we discovered that lateral category-selective regions respond to visual transients associated with stimulus onsets and offsets but not sustained visual information. Thus, lateral category-selective regions compute moment-tomoment visual transitions, but not stable features of the visual input. In contrast, ventral category-selective regions respond to both sustained and transient components of the visual input. Responses to sustained stimuli exhibit adaptation, whereas responses to transient stimuli are surprisingly larger for stimulus offsets than onsets. This large offset transient response may reflect a memory trace of the stimulus when it is no longer visible, whereas the onset transient response may reflect rapid processing of new items. Together, these findings reveal previously unconsidered, fundamental temporal mechanisms that distinguish visual streams in the human brain. Importantly, our results underscore the promise of modeling brain responses with millisecond precision to understand the underlying neural computations.\n\nAUTHOR SUMMARYHow does the brain encode the timing of our visual experience? Using functional magnetic resonance imaging (fMRI) and a temporal encoding model with millisecond resolution, we discovered that visual regions in the lateral and ventral processing streams fundamentally differ in their temporal processing of the visual input. Regions in lateral temporal cortex process visual transients associated with stimulus onsets and offsets but not the unchanging aspects of the visual input. That is, they compute moment-to-moment changes in the visual input. In contrast, regions in ventral temporal cortex process both stable and transient components, with the former exhibiting adaptation. Surprisingly, in these ventral regions responses to stimulus offsets were larger than onsets. We suggest that the former may reflect a memory trace of the stimulus, when it is no longer visible, and the latter may reflect rapid processing of new items at stimulus onset. Together, these findings (i) reveal a fundamental temporal mechanism that distinguishes visual streams and (ii) highlight both the importance and utility of modeling brain responses with millisecond precision to understand the temporal dynamics of neural computations in the human brain.

neuroscience↗

bioRxiv2018

Learning to read increases the informativeness of distributed ventral temporal responses

Becoming a proficient reader requires substantial learning over many years. However, it is unknown how learning to read affects development of distributed visual representations across human ventral temporal cortex (VTC). Using fMRI and a data-driven, computational approach, we quantified the development of distributed VTC responses to characters (pseudowords and numbers) vs. other domains in children, preteens, and adults. Results reveal anatomical- and hemisphere-specific development. With development, distributed responses to words and characters became more distinctive and informative in lateral but not medial VTC, and in the left but not right hemisphere. While development of voxels with both positive (that is, word-selective) and negative preference to words affected distributed information, only development of word-selective voxels predicted reading ability. These data show that developmental increases in informativeness of distributed left lateral VTC responses enable proficient reading and have important implications for both developmental theories and for elucidating neural mechanisms of reading disabilities.

neuroscience↗

bioRxiv2017

Development differentially sculpts receptive fields across human visual cortex

Receptive fields (RFs) processing information in restricted parts of the visual field are a key property of neurons in the visual system. However, how RFs develop in humans is unknown. Using fMRI and population receptive field (pRF) modeling in children and adults, we determined where and how pRFs develop across the ventral visual stream. We find that pRF properties in visual field maps, V1 through VO1, are adult-like by age 5. However, pRF properties in face- and word-selective regions develop into adulthood, increasing the foveal representation and the visual field coverage for faces in the right hemisphere and words in the left hemisphere. Eye-tracking indicates that pRF changes are related to changing fixation patterns on words and faces across development. These findings suggest a link between viewing behavior of faces and words and the differential development of pRFs across visual cortex, potentially due to competition on foveal coverage.

neuroscience↗

bioRxiv2017

An encoding model of temporal processing in human visual cortex

ABSTRACTHow is temporal information processed in human visual cortex? Visual input is relayed to V1 through segregated transient and sustained channels in the retina and LGN. However, there is intense debate as to how transient and sustained channels contribute to visual processing beyond V1. Using a 2 temporal-channel encoding model we can predict fMRI responses to time-varying stimuli ranging from milliseconds to seconds. The transient channel dominates responses in the periphery of early visual cortex and lateral occipito-temporal regions. However, both sustained and transient channels drive responses in central early visual cortex and ventral occipito-temporal regions. Together these finding resolve an outstanding debate and lay the foundation for a complete temporal model of neural processing in visual cortex. Importantly, this encoding approach can be applied with fMRI to decipher neural computations in millisecond resolution in any part of the brain, which has vast implications for understanding neural processing.

neuroscience↗