Littérature scientifique sur le sujet « Occipito-temporal cortex »

A fundamental question for social cognitive neuroscience is how and where in the brain the identities and actions of others are represented. Here we present a replication and extension of a study by Kable and Chatterjee [Kable, J. W., & Chatterjee, A. Specificity of action representations in the lateral occipito-temporal cortex. Journal of Cognitive Neuroscience, 18, 1498–1517, 2006] examining the role of occipito-temporal cortex in these processes. We presented full-cue movies of actors performing whole-body actions and used fMRI to test for action- and identity-specific adaptation effects. We examined a series of functionally defined regions, including the extrastriate and fusiform body areas, the fusiform face area, the parahippocampal place area, the lateral occipital complex, the right posterior superior temporal sulcus, and motion-selective area hMT+. These regions were analyzed with both standard univariate measures as well as multivoxel pattern analyses. Additionally, we performed whole-brain tests for significant adaptation effects. We found significant action-specific adaptation in many areas, but no evidence for identity-specific adaptation. We argue that this finding could be explained by differences in the familiarity of the stimuli presented: The actions shown were familiar but the actors performing the actions were unfamiliar. However, in contrast to previous findings, we found that the action adaptation effect could not be conclusively tied to specific functionally defined regions. Instead, our results suggest that the adaptation to previously seen actions across identities is a widespread effect, evident across lateral and ventral occipito-temporal cortex.

The visual occipito-temporal cortex is composed of several distinct regions specialized in the identification of different object kinds such as tools and bodies. Its organization appears to reflect not only the visual characteristics of the inputs but also the behavior that can be achieved with them. For example, there are spatially overlapping responses for viewing hands and tools, which is likely due to their common role in object-directed actions. How dependent is occipito-temporal cortex organization on object manipulation and motor experience? To investigate this question, we studied five individuals born without hands (individuals with upper limb dysplasia), who use tools with their feet. Using fMRI, we found the typical selective hand–tool overlap (HTO) not only in typically developed control participants but also in four of the five dysplasics. Functional connectivity of the HTO in the dysplasics also showed a largely similar pattern as in the controls. The preservation of functional organization in the dysplasics suggests that occipito-temporal cortex specialization is driven largely by inherited connectivity constraints that do not require sensorimotor experience. These findings complement discoveries of intact functional organization of the occipito-temporal cortex in people born blind, supporting an organization largely independent of any one specific sensory or motor experience.

The Müller-Lyer illusion occurs both in vision and in touch, and transfers cross-modally from vision to haptics [Mancini, F., Bricolo, E., & Vallar, G. Multisensory integration in the Müller-Lyer illusion: From vision to haptics. Quarterly Journal of Experimental Psychology, 63, 818–830, 2010]. Recent evidence suggests that the neural underpinnings of the Müller-Lyer illusion in the visual modality involve the bilateral lateral occipital complex (LOC) and right superior parietal cortex (SPC). Conversely, the neural correlates of the haptic and cross-modal illusions have never been investigated previously. Here we used repetitive TMS (rTMS) to address the causal role of the regions activated by the visual illusion in the generation of the visual, haptic, and cross-modal visuo-haptic illusory effects, investigating putative modality-specific versus cross-modal underlying processes. rTMS was administered to the right and the left hemisphere, over occipito-temporal cortex or SPC. rTMS over left and right occipito-temporal cortex impaired both unisensory (visual, haptic) and cross-modal processing of the illusion in a similar fashion. Conversely, rTMS interference over left and right SPC did not affect the illusion in any modality. These results demonstrate the causal involvement of bilateral occipito-temporal cortex in the representation of the visual, haptic, and cross-modal Müller-Lyer illusion, in favor of the hypothesis of shared underlying processes. This indicates that occipito-temporal cortex plays a cross-modal role in perception both of illusory and nonillusory shapes.

Specific regions of the human occipito-temporal cortex are consistently activated in functional imaging studies of face processing. To understand the contribution of these regions to face processing, we examined the pattern of fMRI activation in four congenital prosopagnosic (CP) individuals who are markedly impaired at face processing despite normal vision and intelligence, and with no evidence of brain damage. These individuals evinced a normal pattern of fMRI activation in the fusiform gyrus (FFA) and in other ventral occipito-temporal areas, in response to faces, buildings, and other objects, shown both as line drawings in detection and discrimination tasks and under more naturalistic testing conditions when no task was required. CP individuals also showed normal adaptation levels in a block-design adaptation experiment and, like control subjects, exhibited evidence of global face representation in the FFA. The absence of a BOLD-behavioral correlation (profound behavioral deficit, normal face-related activation in the ventral occipito-temporal cortex) challenges existing accounts of face representation, and suggests that activation in these cortical regions per se is not sufficient to ensure intact face processing.

It is well established that the human visual system contains a distributed network of regions that are involved in processing faces, but our understanding of how faces are represented within these face-sensitive brain areas is incomplete. We used fMRI to investigate whether face-sensitive brain areas are solely tuned for whole faces, or whether they contain heterogeneous populations of neurons tuned to individual components of the face as well as whole faces, as suggested by physiological investigations in nonhuman primates. The middle fusiform gyrus (fusiform face area, or FFA) and the inferior occipital gyrus (occipital face area, or OFA) produced robust BOLD activation to synthetic whole face stimuli, but also to the internal facial features and head outlines. BOLD responses to whole face stimuli in FFA were significantly reduced after adaptation to whole faces, but not after adaptation to features or head outlines, whereas activation to head outlines was reduced after adaptation to both whole faces and head outlines. OFA showed no significant adaptation effects for matching adaptation and test conditions, but did exhibit cross-adaptation between whole faces and head outlines. The internal face features did not produce any significant adaptation within either FFA or OFA. Our results are consistent with a model in which independent populations of whole face-, feature-, and head outline-tuned neurons exist within face-sensitive regions of human occipito-temporal cortex, which in turn would support tasks such as viewpoint processing, emotion classification, and identity discrimination.

Abstract Human visual cortex contains many retinotopic and category-specific regions. These brain regions have been the focus of a large body of functional magnetic resonance imaging research, significantly expanding our understanding of visual processing. As studying these regions requires accurate localization of their cortical location, researchers perform functional localizer scans to identify these regions in each individual. However, it is not always possible to conduct these localizer scans. Here, we developed and validated a functional region of interest (ROI) atlas of early visual and category-selective regions in human ventral and lateral occipito-temporal cortex. Results show that for the majority of functionally defined ROIs, cortex-based alignment results in lower between-subject variability compared to nonlinear volumetric alignment. Furthermore, we demonstrate that 1) the atlas accurately predicts the location of an independent dataset of ventral temporal cortex ROIs and other atlases of place selectivity, motion selectivity, and retinotopy. Next, 2) we show that the majority of voxel within our atlas is responding mostly to the labeled category in a left-out subject cross-validation, demonstrating the utility of this atlas. The functional atlas is publicly available (download.brainvoyager.com/data/visfAtlas.zip) and can help identify the location of these regions in healthy subjects as well as populations (e.g., blind people, infants) in which functional localizers cannot be run.

Congenital prosopagnosia is a severe impairment in face identification manifested from early childhood in the absence of any evident brain lesion. In this study, we used fMRI to compare the brain activity elicited by faces in a congenital prosopagnosic subject (YT) relative to a control group of 12 subjects in an attempt to shed more light on the nature of the brain mechanisms subserving face identification. The face-related activation pattern of YT in the ventral occipito-temporal cortex was similar to that observed in the control group on several parameters: anatomical location, activation profiles, and hemispheric laterality. In addition, using a modified vase – face illusion, we found that YT's brain activity in the face-related regions manifested global grouping processes. However, subtle differences in the degree of selectivity between objects and faces were observed in the lateral occipital cortex. These data suggest that face-related activation in the ventral occipito-temporal cortex, although necessary, might not be sufficient by itself for normal face identification.

Previous functional neuroimaging studies of reading in skilled readers, acquired dyslexia and developmental dyslexia have all shown that the left ventral occipito-temporal cortex (vOT) is involved in visual word recognition. Specifically, a region in the left posterior occipito-temporal sulcus lateral to fusiform gyrus and medial to inferior temporal gyrus has been reported to play an important role. However, the precise functional contribution of this area in reading is yet to be fully explored. In this thesis, I empirically evaluated a claim that vOT responds not only to bottom-up processing demands of the visual stimuli but is also influenced by automatic, top-down non-visual processing demands, as proposed by the Interactive Account of vOT functioning. The first part of this thesis investigated the functional properties of vOT during reading, using functional magnetic resonance imaging. In the first project, the top-down influences on vOT were investigated, teasing apart visual and non-visual properties of written stimuli. In the second project, using the Japanese orthography I disentangled a word’s lexical frequency from the frequency of its visual form – an important distinction for understanding the neural information processing in regions engaged by reading and further explored the interactive nature of the vOT responses. The second part then investigated the anatomical basis of these functional interactions between vOT and other cortical regions. I used diffusion-weighted magnetic resonance imaging and tractography, the only method currently available to identify and measure white matter fibre pathways non-invasively and in vivo. My research has demonstrated that vOT integrates bottom-up visual information and top-down predictions from regions encoding non-visual attributes of the stimulus in an interactive fashion. It also illustrated the putative anatomical basis for functional connectivity during reading, which is consistent with the parallel cortical visual pathways seen in other primates. Altogether, the results provide strong support for the Interactive Account.

Reading is a multicomponent task that involves basic visuoperceptive, oculomotor and attentional skills (Aghababian and Nazir 2000; Hyona and Olson 1995; Levy, et al. 2010; Rayner1986; Shaywitz and Shaywitz 2008), together with access to symbolic orthographic and lexico-semantic knowledge and the activation of phonological representations (Coltheart, et al. 1997; Plaut, et al. 1996; Zorzi, et al. 1998). Numerous studies have been published that investigated the neural network involved in single word or pseudoword reading in subjects with normal reading abilities and in subjects with developmental dyslexia, using both behavioural and neuroimaging tecnique (Cornelissen et al., 1995; Fawcett & Nicolson, 1994; Finch et al., 2002; Laycock et al., 2008; Nicolson & Fawcett, 1993; Ramus et al., 2003; Snowling, 1981; Stein, 2003; Steinbrink et al., 2008). Given the complexity of reading system and the heterogeneity of the behavioural pattern observed in dyslexic subjects, a wide range of possible explanations have been suggested for dyslexia, such as (i) a specific linguistic problem due to a deficit in phonological processing (Frith, 1999; Ramus et al., 2003; Snowling, 2001), (ii) an impairment of the magnocellular pathway (Eden, VanMeter, Rumsey, & Zeffiro, 1996; A. M. Galaburda, 1993; Hari & Renvall, 2001; Stein, 2001) and (iii) a disfunction of the cerebellar system (D. V. Bishop, 2002; Nicolson et al., 2001; Rae et al., 2002). Each of these theories has found support in behavioural and/or imaging experiments, suggesting that all the systems have an important role in reading process and that they interact with reading process throught anatomofunctional convergence mechanisms. Thus, we used fMRI to explore the extent of the anatomical overlap between the auditory phonological, the visual magnocellular and the motor/cerebellar systems with reading, in order to isolate “interface” areas, that is, regions that are involved in different cognitive systems relevant for reading (Damasio, 1989). Twenty-eight normal subjects performed, after a neuropsychological screening, five tasks during fMRI scans: word and non-word reading, auditory rhyming for letter names, visual motion perception and a motor sequence learning task. We found a rostro-caudal functional gradient in the left occipitotemporal cortex (van der Mark et al., 2011): an anterior area that was activated by both reading and auditory rhyming tasks; a posterior area, commonly activated by both reading and the motion perception task and a medial area, including the so called Visual Word Form Area (Cohen et al., 2002). that was specifically activated by the reading task. On the contrary, the reading and the motor/cerebellar systems showed an overlap in left premotor ventral area and in the cerebellum, bilaterally. These data were in line with the hypothesis that the left occipito-temporal cortex, broadly considered, is an interface area (Devlin et al., 2006) between the reading system and the phonological and magnocellular systems, even if no single area emerged as a convergence area of all the systems. In the light of these evidence, we investigated the areas of reduced activations in a group of dyslexic subjects during a non-word reading task. 12 dyslexic, well compensated, adults were tested with the same previous tasks tackling non-word reading, phonological awareness, visual motion perception and motor learning skills at both behavioural and neurofunctional levels. The behavioural tests confirmed, at the group level, the presence of a phonological disorder, together with the reading deficit, while no between-group differences emerged in the magnocellular and motor/cerebellar tasks. However, the single-subject analyses showed that reduced performance in reading and in phonological tasks was occasionally associated with a reduced performance in tasks designed to test magnocellular visual or the motor “cerebellar” systems. At the anatomofunctional level, fMRI data confirmed that dyslexics had reduced activation of the left inferior-temporal and ventral occipito-temporal cortices for word and non-word reading (Paulesu et al., 2001; Richlan et al., 2009; S. E. Shaywitz et al., 1998). We also observed that these reduced activations associated with non-word reading in dyslexics involved the visual/orthographic and the orthographic/phonological interface area, together with the ventral area specifically activated by the reading task, observed in the previous experiment. On the contrary, the reduced hypoactivations observed in dyslexic subjects during the word reading task not showed an overlap with the more posterior region, such as the visuo-orthografic interface area was involved in sublexical processes and was less stressed by this type of stimulus, while an overlap emerged between this hypoactivated region and the orthographic-phonological area and the reading per sè area. Moreover, there were also hyperactivations in domain specific regions in the visuo/magnocellular and in the motor/cerebellar tasks. Given the normal performance of dyslexic in these tasks at the behavioural level, we hypothesize that these hyperactivations may represent a possible sign of successfull compensatory processes. However, the phonological and the reading speed deficit did stand above other difficulties being evident at both behavioural and physiological level, while the other systems may have undergone a more efficient compensation because of a more redundant neuronal architecture. Finally, I describe the data of a single-case study on a “rare” left hemispherectomized patient. We studied the linguistic behaviour and neurolinguistic organization of a 14 years-old adolescent who underwent a left hemispherectomy at age 2.5. The aphasia observed after surgery was a clear sign of an initial left language lateralization. This study allowed us to evaluate the hypothesis that the occipito-temporal competence could develop in the non dominant hemisphere, together with the behavioural linguistic recovery. EB's neuropsychological pattern was akin to that of a surface dyslexia patient (K. Patterson, Marshall, & Coltheart, 1985): EB made significantly more errors than controls in a visual lexical decision task, in discriminating written homophones and in reading irregular and loan words, even if he did not show a pathological performance in regular word and non-word reading. At anatomofunctional level, EB’s fMRI patterns were similar to those observed in the dominant hemisphere of controls: in both EB and controls the frontal regions, the middle and inferior temporal gyri and the calcarine cortex were activated during word and non-word reading, while reduced activations were observed, in EB than controls, in the angular gyrus and in the occipito-temporal cortex. In particular, the occipito-temporal region was not completely deprived of its functional role, as demonstrated by its “normal” activation in a more elementary shape-matching task; nonetheless, there was no plain commitment of that brain region for reading, as observed in controls. Notwithstanding, the findings from a single case-study deserve great interpretative caution and any attempt toward general conclusions must be tempered with prudence, the communality between the EB’s activations and the haemodynamic response observed in the dominant hemisphere of controls, together with the EB’s behavioural profile, suggested that the neurolinguistic development of EB was similar to the one resulting from the left hemisphere.

L'acte de lire représente une activité devenue parfaitement automatique et constitue un outil permettant de s'inscrire et de participer au monde social et culturel qui nous entoure. L'acquisition de la lecture requiert un apprentissage long et laborieux. Il repose sur la capacité des lecteurs à identifier correctement des stimuli visuels complexes à un degré tel qu'ils doivent pouvoir distinguer " lion " et " loin " ou " foin " en une seule et unique fixation. Par conséquent, le codage de l'identité et de la position de la lettre est crucial dans l'identification visuelle des mots. Ce travail de thèse s'inscrit dans ce cadre de recherche et présente deux objectifs principaux. Premièrement, nous voulions explorer la façon dont le codage de l'identité et la position de la lettre est modulé par le contexte orthographique au cours de l'acquisition de la lecture et dans le cadre de la dyslexie de développement. Les participants réalisaient une tâche de comparaison de séquences de lettres dans laquelle ils devaient juger si deux suites de lettres présentées successivement et brièvement étaient identiques ou différentes. L'identité et la position des lettres étaient manipulées par le biais d'une substitution ou d'une transposition de deux lettres au sein de la séquence. Des non-mots, des pseudo-mots et des mots ont été utilisés comme stimuli pour étudier les effets lexicaux et sub-lexicaux sur l'encodage des lettres. Les résultats montrent que le traitement orthographique (codage de l'identité et de la position des lettres) et la représentation lexicale sont soumis à des changements développementaux et sont altérés chez les enfants dyslexiques. Un trouble de l'empan visuo-attentionnel (VA), i. E. Une capacité VA réduite, chez ces enfants dyslexiques permet de rendre compte de ces perturbations. Deuxièmement, nous voulions explorer, en utilisant l'IRMf, les substrats neurobiologiques du codage de l'identité et de la position des lettres en contexte non-mot chez des adultes normo-lecteurs et dyslexiques. Les normo-lecteurs montrent une forte activation dans les régions pariétales et l'aire occipito-temporale ventrale (VOT) en condition de substitution de lettres, tandis que ces activations sont absentes chez les dyslexiques. Chez les normo-lecteurs, la condition de transposition de lettres active un réseau cortical plus limité, incluant l'aire VOT, laquelle n'est pas activée chez les participants dyslexiques. Ces résultats conduisent à mieux le rôle des régions pariétales et VOT dans la phase précoce du traitement visuel des mots en lecture et dans le cadre de la dyslexie développementale
With time and practice, reading becomes a fully automatized activity that acts as an essential tool for our insertion in the social and cultural world around us. The acquisition of reading is long and laborious and relies on the readers' capacity to properly identify complex visual stimuli at such a fine degree that 'causal' must be discriminated from 'casual' within a single fixation. Consequently, letter-identity and letter-position encoding are crucial for visual identification of words. This thesis work fits into this research framework and investigates two main issues. First, we aimed to explore how letter-identity and letter-position encoding are modulated by letter context during reading acquisition and in developmental dyslexia. A letter-string comparison task was administered to participants who had to judge whether two successively and briefly presented letter strings were identical or different. Letter-position and letter-identity were manipulated through the transposition or substitution of two letters. Non-words, pseudo-words, and words were used as stimuli to investigate sub-lexical and lexical effects on letter encoding. Results show that orthographic processing (letter-identity and letter-position encoding) and lexical representations are subject to developmental changes and are strongly impaired in dyslexic children. A disorder of visuo-attention (VA) span, i. E. A reduced VA capacity, in these dyslexic children might account for this deficit. Secondly, using fMRI, we investigated the neurobiological substrates of letter-position and letter-identity encoding in non-word context in normal and dyslexic adults. Healthy readers activate the parietal and ventral occipito-temporal (VOT) areas in the substitution condition, while dyslexics do not. In healthy readers, the transposition condition activates a more limited cortical network including VOT area, which was not activated in dyslexic participants. These findings provide new insights on the role of parietal and VOT regions in the early phase of visual word processing in reading and developmental dyslexia

Nous proposons un protocole expérimental alliant une période d'amorçage avec des stimuli en présentation unique pour étudier l'implication des cortex visuels associatifs dans la perception de stimuli linguistiques élémentaires. Pour cela, 2 sets de stimuli sont utilisés, l'un linguistique (des lettres uniques), l'autre non-linguistique (des figures géométriques simples) et un stimulus ambigu (le " O "), qui, sous les mêmes caractéristiques physiques, peut être interprété soit comme une lettre soit comme une figure géométrique. Une première étude a été menée en IRM fonctionnelle événementielle. Une analyse de groupe puis deux analyses à partir des données individuelles (l'une fondée sur l'étendue des activations, l'autre sur l'intensité du signal) ont montré une spécialisation du cortex occipito-temporal gauche dans le traitement des graphèmes. .
We propose an experimental design based on a priming paradigm with single visual stimuli to study the role of extrastriate cortex in the perceptual processing of simple linguistic stimuli. We used two sets of stimuli, a linguistic one that consisted of single letters, and a non-linguistic one that consisted of familiar geometric figures; in addition, the ambiguous stimulus "O", which could be categorized either as a letter or as a familiar geometric figure, was primed by both categorical sets. A first study was conducted with an event-related fMRI protocol. The group analysis and the individual analysis on both the extend and intensity of activations showed that the left occipito-temporal cortex was specifically involved in grapheme processing. .

The sensitivity of the left ventral occipito-temporal (vOT) cortex to visual word processing has triggered a considerable debate about the functional role of this region in reading. The debate rests largely on the issue whether this particular region is specifically dedicated to reading and the extraction of invariant visual word form. A lot of studies have been conducted to provide evidences supporting or against the functional specialization of this region. However, the trend is showing that the different functional properties proposed by the two kinds of view are not in conflict with each other, but instead show different sides of the same fact. Here, the authors focus on two questions: firstly, where do the two views conflict, and secondly, how do they fit with each other on a larger framework of functional organization in object vision pathway? This review evaluates findings from the two sides of the debate for a broader understanding of the functional role of the left vOT cortex.