Biology subjects

Rezk, M.

Publications and source records attributed to Rezk, M..

11 recordsLinked to original sources

bioRxiv2025

Representation of emotional expressions across the face and voice brain networks

Recognizing emotion expressions from facial and vocal signals is crucial for optimal social interactions. We comprehensively characterized regions within the face and voice processing networks to probe their contribution to unimodal and crossmodal emotion representation. Using multivariate pattern classification analyses, we found that emotional expressions could be reliably decoded from the dominant sensory modality in all individually defined face- and voice-selective regions. Emotion expressions from the non-dominant modality (vocal expressions in the face networks, and vice versa) could also be decoded in all areas except the occipital face areas. A shared neural code for facial and vocal emotions is implemented in the temporal voice areas (TVA), the posterior superior temporal sulcus (pSTS) and the precentral gyrus (PCG). The simultaneous presentation of congruent facial and vocal expressions elicited distinct activity patterns across most regions, highlighting that multisensory inputs reshape brain responses relative to unisensory stimulation across the entire face and voice brain network. These findings suggest that face and voice-selective regions broadly encode emotion expressions within and even across the senses, relying on a multisensory gradient that converges in temporo-frontal regions where their distributed multisensory responses align to create a supramodal representation of specific emotion expressions.

neuroscience↗

bioRxiv2024

Impact of a transient neonatal visual deprivation on the development of the ventral occipito-temporal cortex in humans

How does experience shape the development of visual brain regions? We demonstrate that a transient period of visual deprivation early in life in humans leads to permanent alteration in the function of the early visual cortex (EVC), while leaving the categorical coding of downstream ventral occipito-temporal cortex (VOTC) mostly unaffected. We used fMRI to characterize the brain response to five categories (faces, bodies, objects, buildings and words) in a rare group of cataract-reversal individuals who experienced a transient period of blindness early in life, and in matched participants with typical visual development. We show that the encoding of low-level visual properties is impaired in EVC in cataract-reversal participants, while the categorical response in the VOTC is preserved. When altering the visual properties of our stimuli to mimic in controls the deficit of EVC response of the cataract, we observe a cascading alteration of the categorical coding from EVC to VOTC that is not observed in the cataract-reversal group. Our results show that a typical visual categorical organization develops in VOTC despite a period of visual deprivation early in life and in the presence of impaired processing in EVC. A deep neural network exposed to a visual diet that emulates the experience of our participants reproduced our brain observations within an artificial system. These findings emphasize how specific visual regions are differently affected by a period of visual deprivation early in life, with information encoded in EVC being permanently affected, while the categorical coding in VOTC shows resilience to deprivation.

neuroscience↗

bioRxiv2021

Structural and functional network-level reorganization in the coding of auditory motion directions and sound source locations in the absence of vision

hMT+/V5 is a region in the middle occipito-temporal cortex that responds preferentially to visual motion in sighted people. In case of early visual deprivation, hMT+/V5 enhances its response to moving sounds. Whether hMT+/V5 contains information about motion directions and whether the functional enhancement observed in the blind is motion specific, or also involves sound source location, remains unsolved. Moreover, the impact of this crossmodal reorganization of hMT+/V5 on the regions typically supporting auditory motion processing, like the human Planum Temporale (hPT), remains equivocal. We used a combined functional and diffusion MRI approach and individual in-ear recordings to study the impact of early blindness on the brain networks supporting spatial hearing, in male and female humans. Whole-brain univariate analysis revealed that the anterior portion of hMT+/V5 responded to moving sounds in sighted and blind people, while the posterior portion was selective to moving sounds only in blind participants. Multivariate decoding analysis revealed that the presence of motion directions and sound positions information was higher in hMT+/V5 and lower in hPT in the blind group. While both groups showed axis-of-motion organization in hMT+/V5 and hPT, this organization was reduced in the hPT of blind people. Diffusion MRI revealed that the strength of hMT+/V5 - hPT connectivity did not differ between groups, whereas the microstructure of the connections was altered by blindness. Our results suggest that the axis-of-motion organization of hMT+/V5 does not depend on visual experience, but that blindness alters the response properties of occipito-temporal networks supporting spatial hearing in the sighted. Significance StatementSpatial hearing helps living organisms navigate their environment. This is certainly even more true in people born blind. How does blindness affect the brain network supporting auditory motion and sound source location? Our results show that the presence of motion directions and sound positions information was higher in hMT+/V5 and lower in hPT in blind relative to sighted people; and that this functional reorganization is accompanied by microstructural (but not macrostructural) alterations in their connections. These findings suggest that blindness alters crossmodal responses between connected areas that share the same computational goals.

neuroscience↗

bioRxiv2020

The balanced act of crossmodal and intramodal plasticity for processing sound categories in early and late onset blindness

How does blindness onset impact on the organization of cortical regions coding for the deprived and the remaining senses? We show that the coding of sound categories in the occipital cortex is enhanced and more stable within and across blind individuals when compared to sighted controls, while a reverse group difference is found in the temporal cortex. Importantly, occipital and temporal regions share a more similar representational structure in blind people, suggesting an interplay between the reorganization of occipital and temporal regions following visual deprivation. We suggest that early, and to some extent late blindness, induces network-level reorganization of the neurobiology of auditory categories by concomitantly increasing/decreasing the respective computational load of occipital/temporal regions. These results highlight the interactive nature of regional brain development in case of sensory deprivation.

neuroscience↗

bioRxiv2020

Visual motion processing recruits regions selective for auditory motion in early deaf individuals

In early deaf individuals, the auditory deprived temporal brain regions become engaged in visual processing. In our study we tested further the hypothesis that intrinsic functional specialization guides the expression of cross-modal responses in the deprived auditory cortex. We used functional MRI to characterize the brain response to horizontal, radial and stochastic visual motion in early deaf and hearing individuals matched for the use of oral or sign language. Visual motion showed enhanced response in the deaf mid-lateral planum temporale, a region selective to auditory motion as demonstrated by a separate auditory motion localizer in hearing people. Moreover, multivariate pattern analysis revealed that this reorganized temporal region showed enhanced decoding of motion categories in the deaf group, while visual motion-selective region hMT+/V5 showed reduced decoding when compared to hearing people. Dynamic Causal Modelling revealed that the deaf motion-selective temporal region shows a specific increase of its functional interactions with hMT+/V5 and is now part of a large-scale visual motion selective network. In addition, we observed preferential responses to radial, compared to horizontal, visual motion in the deaf right superior temporal cortex region that also show preferential response to approaching/receding sounds in the hearing brain. Overall, our results suggest that the early experience of auditory deprivation interacts with intrinsic constraints and triggers a large-scale reallocation of computational load between auditory and visual brain regions that typically support the multisensory processing of motion information. HighlightsO_LIAuditory motion-sensitive regions respond to visual motion in the deaf C_LIO_LIReorganized auditory cortex can discriminate between visual motion trajectories C_LIO_LIPart of the deaf auditory cortex shows preference for in-depth visual motion C_LIO_LIDeafness might lead to computational reallocation between auditory/visual regions. C_LI

neuroscience↗

bioRxiv2020

Direct structural connections between auditory and visual motion selective regions in humans

In humans, the occipital middle-temporal region (hMT+/V5) specializes in the processing of visual motion, while the Planum Temporale (hPT) specializes in auditory motion processing. It has been hypothesized that these regions might communicate directly to achieve fast and optimal exchange of multisensory motion information. In this study, we investigated for the first time in humans the existence of direct white matter connections between visual and auditory motion-selective regions using a combined functional- and diffusion-MRI approach. We found reliable evidence supporting the existence of direct white matter connections between individually and functionally defined hMT+/V5 and hPT. We show that projections between hMT+/V5 and hPT do not overlap with large white matter bundles such as the Inferior Longitudinal Fasciculus (ILF) nor the Inferior Frontal Occipital Fasciculus (IFOF). Moreover, we did not find evidence for the existence of reciprocal projections between the face fusiform area and hPT, supporting the functional specificity of hMT+/V5 - hPT connections. Finally, evidence supporting the existence of hMT+/V5 - hPT connections was corroborated in a large sample of participants (n=114) from the human connectome project. Altogether, this study provides first evidence supporting the existence of direct occipito-temporal projections between hMT+/V5 and hPT which may support the exchange of motion information between functionally specialized auditory and visual regions and that we propose to name the middle (or motion) occipito-temporal track (MOTT).

neuroscience↗

bioRxiv2019

Similar categorical representation from sound and sight in the occipito-temporal cortex of sighted and blind

Is vision necessary for the development of the categorical organization of the Ventral Occipito-Temporal Cortex (VOTC)? We used fMRI to characterize VOTC responses to eight categories presented acoustically in sighted and early blind individuals, and visually in a separate sighted group. We observed that VOTC reliably encodes sound categories in sighted and blind people using a representational structure and connectivity partially similar to the one found in vision. Sound categories were, however, more reliably encoded in the blind than the sighted group, using a representational format closer to the one found in vision. Crucially, VOTC in blind represents the categorical membership of sounds rather than their acoustic features. Our results suggest that sounds trigger categorical responses in the VOTC of congenitally blind and sighted people that partially match the topography and functional profile of the visual response, despite qualitative nuances in the categorical organization of VOTC between modalities and groups.

neuroscience↗

bioRxiv2018

Recruitment of occipital cortex by arithmetic processing follows computational bias in early blind

Arithmetic reasoning activates the occipital cortex of early blind people (EB). This activation of visual areas may reflect functional flexibility or the intrinsic computational role of specific occipital regions. We contrasted these competing hypotheses by characterizing the brain activity of EB and sighted participants while performing subtraction, multiplication and a control verbal task. In both groups, subtraction selectively activated a bilateral dorsal network commonly activated during spatial processing. Multiplication triggered more activity in temporal regions thought to participate in memory retrieval. No between-group difference was observed for the multiplication task whereas subtraction induced enhanced activity in the right dorsal occipital cortex of the blind individuals only. As this area overlaps and exhibits increased functional connectivity with regions showing selective tuning to auditory spatial processing, our results suggest that the recruitment of occipital regions during high-level cognition in the blind actually relates to the intrinsic computational role of the reorganized regions.

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bioRxiv2017

Functional selectivity for face processing in the temporal voice area of early deaf individuals

Brain systems supporting face and voice processing both contribute to the extraction of important information for social interaction (e.g., person identity). How does the brain reorganize when one of these channels is absent? Here we explore this question by combining behavioral and multimodal neuroimaging measures (magneto-encephalography and functional imaging) in a group of early deaf humans. We show enhanced selective neural response for faces and for individual face coding in a specific region of the auditory cortex that is typically specialized for voice perception in hearing individuals. In this region, selectivity to face signals emerges early in the visual processing hierarchy, shortly following typical face-selective responses in the ventral visual pathway. Functional and effective connectivity analyses suggest reorganization in long-range connections from early visual areas to the face-selective temporal area in individuals with early and profound deafness. Altogether, these observations demonstrate that regions that typically specialize for voice processing in the hearing brain preferentially reorganize for face processing in born deaf people. Our results support the idea that cross-modal plasticity in case of early sensory deprivation relates to the original functional specialization of the reorganized brain regions.

neuroscience↗

bioRxiv2017

Visual experience shapes the neural networks remapping touch into external space

Localizing touch relies on the activation of skin-based and externally defined spatial frames of references. Psychophysical studies have demonstrated that early visual deprivation prevents the automatic remapping of touch into external space. We used fMRI to characterize how visual experience impacts on the brain circuits dedicated to the spatial processing of touch. Sighted and congenitally blind humans (male and female) performed a tactile temporal order judgment (TOJ) task, either with the hands uncrossed or crossed over the body midline. Behavioral data confirmed that crossing the hands has a detrimental effect on TOJ judgments in sighted but not in blind. Crucially, the crossed hand posture elicited more activity in a fronto-parietal network in the sighted group only. Psychophysiological interaction analysis revealed that the congenitally blind showed enhanced functional connectivity between parietal and frontal regions in the crossed versus uncrossed hand postures. Our results demonstrate that visual experience scaffolds the neural implementation of touch perception.\n\nSignificance statementAlthough we seamlessly localize tactile events in our daily life, it is not a trivial operation because the hands move constantly within the peripersonal space. To process touch correctly, the brain has therefore to take the current position of the limbs into account and remap them to their location in the external world. In sighted, parietal and premotor areas support this process. However, while visual experience has been suggested to support the implementation of the automatic external remapping of touch, no studies so far have investigated how early visual deprivation alters the brain network supporting touch localization. Examining this question is therefore crucial to conclusively determine the intrinsic role vision plays in scaffolding the neural implementation of touch perception.

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bioRxiv2017

Functional Preference For Object Sounds But Not For Voices In The Occipito-Temporal Cortex Of Early Blind Individuals

Sounds activate occipital regions in early blind individuals. How different sound categories map onto specific regions of the occipital cortex remains however debated. We used fMRI to characterize brain responses of early blind and sighted individuals to familiar object sounds, human voices and their respective low-level control sounds. Sighted participants were additionally tested when viewing pictures of faces, objects and phase-scrambled control pictures. In both early blind and sighted, a double dissociation was evidenced in bilateral auditory cortices between responses to voices and object sounds: voices elicited categorical responses in bilateral superior temporal sulci while object sounds elicited categorical responses along the lateral fissure bilaterally, including the primary auditory cortex and planum temporale. Outside of the auditory regions, object sounds additionally elicited categorical responses in left lateral and ventral occipito-temporal regions in both groups. These regions also showed response preference for images of objects in the sighted, thus suggesting a functional specialization in these regions that is independent of sensory input and visual experience. Between-group comparisons revealed that only in the blind group, categorical responses to object sounds extended more posteriorly into the occipital cortex. Functional connectivity analyses evidenced a selective increase in the functional coupling between these reorganized regions and regions of the ventral occipito-temporal cortex in the early blind. In contrast, vocal sounds did not elicit preferential responses in the occipital cortex in either group. Nevertheless, enhanced voice-selective connectivity between the left temporal voice area and the right fusiform gyrus were found in the blind. Altogether, these findings suggest that separate auditory categories are not equipotent in driving selective auditory recruitment of occipito-temporal regions in the absence of developmental vision, highlighting domain-region constraints on the expression of crossmodal plasticity.

neuroscience↗