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O sinal de entrada na retina é decomposto em termos de frequência espacial (FE), variações periódicas de luminância ao longo do espaço. Existe vasta literatura sobre o processamento de FE no córtex visual primário. No entanto, não se sabe ao certo como esta informação sensorial básica é processada e integrada numa visão de alto nível. Esta tese aborda este tema ao investigar lateralidade cerebral, tempo de processamento e contexto cognitivo em três diferentes seções com objetivos específicos. Estas seções investigaram comportamentalmente visão de alto nível tendo a face humana como estímulo, dado sua relevância biológica e social. Na primeira seção (Theoretical Review), uma revisão apresenta estudos clínicos e neuropsicológicos que mostram áreas cerebrais envolvidas na percepção de faces e como os hemisférios esquerdo e direito realizam um processamento holístico e analítico baseado em informações de FEs. A especialização hemisférica de FE no reconhecimento de faces é então revisada e discutida. Concluiu-se que assimetrias sensoriais podem ser a base para assimetrias cognitivas de alta ordem. Ademais, foi destacado a influência do tempo de processamento. Na segunda seção (Study 1), foi investigado por método psicofísico a lateralidade de baixas e altas FEs no reconhecimento de faces em diferentes tempos de exposição. Faces com filtragem de FE foram apresentadas em campo visual dividido em alta e baixa restrição temporal em duas tarefas: reconhecimento facial (Experimento 1) e reconhecimento do sexo facial (Experimento 2). No Experimento 1, informações faciais de baixas e altas FEs foram mais eficientemente processadas no hemisfério direito e esquerdo, respectivamente, sem efeito do tempo de exposição das faces. Os resultados do Experimento 2 mostraram uma assimetria do hemisfério direito para baixas FEs em baixa restrição temporal. Conclui-se que o processamento de altas e baixas FEs é lateralizado nos hemisférios cerebrais no reconhecimento de faces. No entanto, a contribuição de altas e baixas FEs é dependente da tarefa e do tempo de exposição. Na terceira seção (Study 2) foi investigado qual estratégia temporal, coarse-to-fine (de baixas para altas FEs) ou fine-to-coarse, cada hemisfério cerebral utiliza para integrar informação de FE de faces humanas numa tarefa de categorização facial homem-mulher. Sequências dinâmicas breves coarse-to-fine e fine-to-coarse de faces foram apresentadas no campo visual esquerdo, direito e central. Os resultados do tempo de resposta e do score de eficiência invertida mostraram uma prevalência geral de um processamento coarse-to-fine, independente do campo visual de apresentação. Ainda, os dados da taxa de erro ressaltam o processamento coarse-to-fine realizado pelo hemisfério direito. No geral, esta tese fornece insights sobre assimetria cerebral funcional, integração de alto nível e curso temporal do processamento de FEs, principalmente para aqueles interessados na percepção de faces. Também foi mostrado que operações lateralizadas, tarefa-dependente e coarse-to-fine podem coexistir e interagir no cérebro para processar informação de FE. / Retinal input is decomposed in terms of spatial frequency (SF), i.e., periodic variations of luminance through space. There is extensive literature on the processing of SF in the primary visual cortex. However, it is still unclear how SF information is processed and integrated in high-level vision. This thesis addressed this issue in terms of laterality effects, processing time-course, and the cognitive context in three different sections with specific purposes. These sections behaviorally tackle high-level vision using human faces as stimuli due to their biological and social relevance. In the first section (Theoretical Review) a literature review presented clinical and neurophysiological studies that show brain areas that are involved in face perception and how the right and left hemispheres perform holistic and analytic processing, depending on SF information. The SF hemispheric specialization in face recognition is then reviewed and discussed. Our conclusion is that functional sensorial asymmetries may be the basis for high-level cognitive asymmetries. In addition, we highlighted the role of the processing time. In the second section (Study 1), we psychophysically investigated laterality of low and high SF in face recognition at different exposure times. The SF filtered faces were presented in a divided visual field at high and low temporal constraint in two tasks: face recognition (Experiment 1) and face gender recognition (Experiment 2). In Experiment 1, low and high SF facial information were more efficiently processed in the right and in the left hemisphere, respectively, with no effect of exposure time. In Experiment 2, results showed a right hemisphere asymmetry for low SF faces at low temporal constraint. We concluded that the processing of low and high SF is lateralized in the brain hemispheres for face recognition. However, low and high SF contribution is dependent on the task and the exposure time. In the third section (Study 2), we aimed to investigate which temporal strategy, i.e., coarse-to-fine (from low to high SF) or fine-to-course, each brain hemisphere performs to integrate SF information of human faces in a male-female categorization task. Coarse-to-fine and fine-to-course brief dynamic sequences of faces were presented in the left, right and central visual field. Results of the correct response time and the inverse efficiency score showed an overall advantage of coarse-to-fine processing, irrespective of the visual field of presentation. Data of the error rate also highlights the role of the right hemisphere in the coarse-to-fine processing. All in all, this thesis provided some insights on functional brain asymmetry, high-level integration, and processing time-course of SF information, mainly for those interested in face perception. It was also shown that lateralized, diagnostic-oriented, and coarse-to-fine operations may coexist and interact in the human brain to process SF information.

O sinal de entrada na retina é decomposto em termos de frequência espacial (FE), variações periódicas de luminância ao longo do espaço. Existe vasta literatura sobre o processamento de FE no córtex visual primário. No entanto, não se sabe ao certo como esta informação sensorial básica é processada e integrada numa visão de alto nível. Esta tese aborda este tema ao investigar lateralidade cerebral, tempo de processamento e contexto cognitivo em três diferentes seções com objetivos específicos. Estas seções investigaram comportamentalmente visão de alto nível tendo a face humana como estímulo, dado sua relevância biológica e social. Na primeira seção (Theoretical Review), uma revisão apresenta estudos clínicos e neuropsicológicos que mostram áreas cerebrais envolvidas na percepção de faces e como os hemisférios esquerdo e direito realizam um processamento holístico e analítico baseado em informações de FEs. A especialização hemisférica de FE no reconhecimento de faces é então revisada e discutida. Concluiu-se que assimetrias sensoriais podem ser a base para assimetrias cognitivas de alta ordem. Ademais, foi destacado a influência do tempo de processamento. Na segunda seção (Study 1), foi investigado por método psicofísico a lateralidade de baixas e altas FEs no reconhecimento de faces em diferentes tempos de exposição. Faces com filtragem de FE foram apresentadas em campo visual dividido em alta e baixa restrição temporal em duas tarefas: reconhecimento facial (Experimento 1) e reconhecimento do sexo facial (Experimento 2). No Experimento 1, informações faciais de baixas e altas FEs foram mais eficientemente processadas no hemisfério direito e esquerdo, respectivamente, sem efeito do tempo de exposição das faces. Os resultados do Experimento 2 mostraram uma assimetria do hemisfério direito para baixas FEs em baixa restrição temporal. Conclui-se que o processamento de altas e baixas FEs é lateralizado nos hemisférios cerebrais no reconhecimento de faces. No entanto, a contribuição de altas e baixas FEs é dependente da tarefa e do tempo de exposição. Na terceira seção (Study 2) foi investigado qual estratégia temporal, coarse-to-fine (de baixas para altas FEs) ou fine-to-coarse, cada hemisfério cerebral utiliza para integrar informação de FE de faces humanas numa tarefa de categorização facial homem-mulher. Sequências dinâmicas breves coarse-to-fine e fine-to-coarse de faces foram apresentadas no campo visual esquerdo, direito e central. Os resultados do tempo de resposta e do score de eficiência invertida mostraram uma prevalência geral de um processamento coarse-to-fine, independente do campo visual de apresentação. Ainda, os dados da taxa de erro ressaltam o processamento coarse-to-fine realizado pelo hemisfério direito. No geral, esta tese fornece insights sobre assimetria cerebral funcional, integração de alto nível e curso temporal do processamento de FEs, principalmente para aqueles interessados na percepção de faces. Também foi mostrado que operações lateralizadas, tarefa-dependente e coarse-to-fine podem coexistir e interagir no cérebro para processar informação de FE. / Retinal input is decomposed in terms of spatial frequency (SF), i.e., periodic variations of luminance through space. There is extensive literature on the processing of SF in the primary visual cortex. However, it is still unclear how SF information is processed and integrated in high-level vision. This thesis addressed this issue in terms of laterality effects, processing time-course, and the cognitive context in three different sections with specific purposes. These sections behaviorally tackle high-level vision using human faces as stimuli due to their biological and social relevance. In the first section (Theoretical Review) a literature review presented clinical and neurophysiological studies that show brain areas that are involved in face perception and how the right and left hemispheres perform holistic and analytic processing, depending on SF information. The SF hemispheric specialization in face recognition is then reviewed and discussed. Our conclusion is that functional sensorial asymmetries may be the basis for high-level cognitive asymmetries. In addition, we highlighted the role of the processing time. In the second section (Study 1), we psychophysically investigated laterality of low and high SF in face recognition at different exposure times. The SF filtered faces were presented in a divided visual field at high and low temporal constraint in two tasks: face recognition (Experiment 1) and face gender recognition (Experiment 2). In Experiment 1, low and high SF facial information were more efficiently processed in the right and in the left hemisphere, respectively, with no effect of exposure time. In Experiment 2, results showed a right hemisphere asymmetry for low SF faces at low temporal constraint. We concluded that the processing of low and high SF is lateralized in the brain hemispheres for face recognition. However, low and high SF contribution is dependent on the task and the exposure time. In the third section (Study 2), we aimed to investigate which temporal strategy, i.e., coarse-to-fine (from low to high SF) or fine-to-course, each brain hemisphere performs to integrate SF information of human faces in a male-female categorization task. Coarse-to-fine and fine-to-course brief dynamic sequences of faces were presented in the left, right and central visual field. Results of the correct response time and the inverse efficiency score showed an overall advantage of coarse-to-fine processing, irrespective of the visual field of presentation. Data of the error rate also highlights the role of the right hemisphere in the coarse-to-fine processing. All in all, this thesis provided some insights on functional brain asymmetry, high-level integration, and processing time-course of SF information, mainly for those interested in face perception. It was also shown that lateralized, diagnostic-oriented, and coarse-to-fine operations may coexist and interact in the human brain to process SF information.

Handedness is a widely studied behavioral asymmetry that is commonly measured as a preference for using one hand over the other. Right hand preference in humans occurs at a ratio of 9:1, whereas left hand preference in rhesus monkeys has been estimated at 2:1. Despite differences in the direction and degree of hand preference, this dissertation investigated whether primates share common underlying factors for the development of handedness. Previous work in human infants has identified a predictive relationship between rightward supine head orientation and later right hand preference. Experiment 1 examined the relationship between neonatal head orientation and later hand use in rhesus monkey infants (N=16). A leftward supine head orientation bias was found that corresponded to greater left hand activity for hand-to-face movements while supine; however, neonatal head positioning did not predict later hand use preference for reaching or manipulation on a coordinated bimanual task. A supine posture is common for human infants, but not for rhesus monkey infants, indicating that differences in early posture experience may differentially shape the development of hand use preference. Movement quality is an additional factor that may affect how the hands are used in addition to neonatal experience. 2-D and 3-D kinematic analyses were used to examine the quality of reaching movements in rhesus monkey infants (N=16), human infants (N=73) and human adults (N=12). In rhesus monkey infants, left hand reaches were characterized as ballistic as compared to right hand reaches independent of hand use preference (Experiment 2). Left hand ballistic reaching in rhesus monkeys may be a carryover from earlier primates that relied on very fast reaches to capture insect prey. Unlike monkey infants, reach quality was a function of hand preference in human infants (Experiment 3). By contrast, a right hand advantage for reaching was observed in human adults regardless of left or right hand preference (Experiment 4). Differential hand experience due to hand preference in early infancy may in part be responsible for the hand preference effects on movement quality observed in human infants but not monkey infants. Motor control may become increasingly lateralized to the left hemisphere over human development leading to the right hand advantage for reaching observed in human adults, as well as over primate evolution leading to right hand use preferences in higher primates like chimpanzees. An underlying mechanism such as a right shift factor in humans and a left shift factor in rhesus monkeys may be a common basis for primate handedness. Environmental and experiential factors then differentially shape this mechanism, including species-typical development. Further work examining the ontogeny of hand preference and hemispheric specialization in various primate infants will lead to a greater understanding of how different factors interact in the development of hand use across primate species.

A crucial aspect of attentional control is the capacity of anticipating a stimulus appearance in order to improve the speed and effectiveness of its subsequent processing. Preparatory attention (PA) is the ability to modulate (enhance) the intensity of attention directed to a selected stimulus prior to its occurrence, preventing subjects from being distracted by interfering stimuli. Some studies propose that PA is lateralized to the right hemisphere (RH) while others suggest that both the left hemisphere (LH) and the RH participate in the modulation of PA. The aim of the present thesis was to examine the role of each brain hemisphere in the modulation of PA directed to a spatial location. We developed a lateralized version of the Attentional Preparatory Test, (APT, proposed par LaBerge, Auclair & Siéroff, 2000), named the Lateralized APT or LAPT. The APT measures the ability of subjects to modulate PA directed to a target location when the probability of a distractor occurrence varies across several blocks of trials. In the APT, the response times increased as the probability of a distractor appearing in the preparatory phase preceding the target presentation increased, showing that PA is modulated by the events occurring prior to the target appearance. We developed the LAPT using the divided visual field paradigm in which stimuli can occur in the left (LVF) or the right (RVF) visual fields. The visual field differences in subjects' performance are assumed to reflect differences in the processing strategies of both hemispheres (RVF/LH vs LVF/RH). In a series of studies we showed that the modulation of PA by the expected probability of events was different in each visual field/hemisphere, depending on task configuration. In the RVF/LH, PA is modulated by the expected probability of distractor events, especially when this probability is explicit. In addition, the LH seems to play a crucial role in modulating PA when the target and the distractor are hard to discriminate. In the LVF/RH, PA is modulated by the temporal probability of events and may depend on the most probable delay in which the target is expected, but only when the discrimination between the target and the distractor is easy. Most importantly, our findings suggest that the differences between RVF/LH and LVF/RH in the modulation of PA take place at the perceptual level of processing because they are independent of the hand use in executing the response, thus also independent of the processes taking place at the motor programming level. Taken together our results, they suggest that each hemisphere uses a different strategy to modulate PA when directed to a spatial location.

This study's purpose was to investigate the phenomenon of hemispheric specialization for the pitch and rhythmic aspects of melody. Its research problems were to investigate the Influence of pitch, rhythm, and training on hemispheric specialization for pitch-plus-rhythm melodic fragments. A final problem was to examine the relationship between dlchotic ear scores and eye movements evidenced during melodic processing. Twenty musicians and twenty nonmuslcians, right-handed and equally divided as to gender, participated in the project. Accepted dlchotic testing and eye behavior indexing procedures were implemented to investigate each research problem. The dlchotic tape produced for the study contained five subtests In which pitch activity was variously greater than, less than, or equal to rhythmic activity.

Ce mémoire consiste à offre un survol des études neuropsychologiques et électrophysiologiques concernant l’interaction possible entre le traitement du langage et la musique. Le but principal est de déterminer les raisons possibles pour lesquelles des locuteurs d’une langue à tons auraient une meilleure capacité dans la perception du contraste du pitch en musique par rapport aux individus qui ont pour langue maternelle une langue à intonation. Dans un premier temps, nous discutons du traitement neuronal de la prosodie et de la musique, tentant de montrer le chevauchement du traitement cérébral des deux domaines. Ensuite, nous présentons des notions d’une langue tonale ainsi que le traitement neuronal des tons lexicaux. Après, nous discutons des effets de transfert de la capacité du traitement du pitch en linguistique et en musique, en nous focalisant sur l’influence de la connaissance native d’une langue tonale sur la perception musicale. Pour ce faire, l’encodage du pitch et la localisation hémisphérique du traitement des tons lexicaux et la musique serons discutés. / This thesis gives an overview of neuropsychological and electrophysiological studies about the possible interaction between the processing of language and music. Our main purpose is to examine the possible reasons for which tone language speakers have a better capacity in perceiving pitch contrast in music than native speakers of an intonational language. First, we discuss the neural processing of prosody and music, attempting to show an overlap between the two domains. Next, we present the concept of a tone langue and the neural processing of lexical tones. Afterwards, we discuss the transfer effects of the processing capacity of pitch in linguistic and music by focusing on the influence of a knowledge of a tone language on the musical perception. To do this, the encoding of pitch and the hemispheric specialization will be discussed.

Les objectifs de ce programme de recherche étaient, d’une part, d’apporter une compréhension critique des techniques non-invasives utilisées dans la localisation et/ou la latéralisation des aires langagières et mnésiques en tenant compte de leurs avantages, de leurs limites propres ainsi que de leur pertinence dans un contexte clinique. D’autre part, d’approfondir notre compréhension de l’organisation cérébrale langagière auprès d’une population de sujets ayant une agénésie du corps calleux en utilisant un protocole de neuroimagerie. Afin de répondre à notre premier objectif, une revue critique de la littérature des méthodes de neuroimagerie utilisées pour la latéralisation et la localisation des aires cérébrales sous-tendant le traitement langagier et mnésique dans le contexte du bilan préchirurgical des patients épileptiques a été effectuée. Ce travail a permis d’identifier que certaines de ces nouvelles techniques et plus spécialement leur combinaison, montrent un potentiel réel dans ce contexte clinique. Cette recherche a également permis de mettre en lumière que ces méthodes ont encore un grand besoin d’être raffinées et standardisées avant d’être utilisées comme remplacement au test à l’amobarbital intracarotidien dans un contexte clinique sécuritaire. Afin de répondre à notre deuxième objectif, nous avons exploré les patrons de latéralisation du langage auprès de six sujets acalleux en utilisant un protocle d’imagerie par résonance magnétique fonctionnelle (IRMf). Les résultats indiquent que les individus ayant une agénésie du corps calleux montrent un patron d’activation cérébrale tout aussi latéralisé que nos deux groupes contrôles (QI apparié et QI élevé) lors du traitement du langage réceptif. Les sujets ayant une agénésie du corps calleux montrent également un patron de latéralisation comparable à leur groupe contrôle apparié pour le QI pour la tâche de langage expressif. Lorsque l’on compare les sujets ayant une agénésie du corps calleux au groupe contrôle de QI élevé, ces derniers montrent une latéralisation moins marquée uniquement pour la région frontale lors de la tâche de langage expressif. En conclusion, les résultats de cette étude ne supportent pas l’affirmation que le corps calleux jouerait un rôle inhibiteur essentiel afin de permettre un développement normal de la latéralisation hémisphérique pour le langage. / The goals of this research program were, on the one end, to bring a critical understanding of the non invasive techniques used for the localisation and lateralisation of language and memory functions taking into account their respective advantages, limits and relevance in a patient care context. On the other end, we wanted to deepen our understanding of cerebral language organization in the context of the study of acallosal subjects. To meet our first objective, we performed a comprehensive review of the litterature of neuroimaging methods used in language and memory lateralisation and localisation in the context of presurgical assessment of epileptic patients. In this work, we pointed out that some of these new methodologies and moreover their combinations show an interesting potential for the use in a clinical context. We also pointed out that these methods still need to be refined and standardised before replacing the intracarotid amobarbital test in a safe clinical setting. To meet our second objective, we explored patterns of language lateralization in six individuals with callosal agenesis using a functional magnetic resonance imaging (fMRI) protocol. No differences were found between language lateralization of subjects with agenesis of the corpus callosum and the control groups (High-IQ and IQ-matched) in the receptive speech task. However, for expressive speech, the groups differed with respect to frontal activations, with the acallosal participants showing a more bilateral pattern of activation than the high-IQ participants only. No differences were found in themporal regions. Overall, these results indicate that the corpus callosum is not essential for the establishment of lateralized language functions.

Bien que l’utilisation précoce de gestes communicatifs par de jeunes enfants soit reconnue comme étant étroitement liée au développement du langage (e.g., Colonnesi et al., 2010), la nature des liens gestes–langage doit encore être clarifiée. Cette thèse a pour but d’étudier la production de gestes de pointage au cours du développement afin de déterminer si la relation prédictive et facilitatrice entre les gestes et l’acquisition du langage implique des fonctions spécifiques du pointage, en association avec des caractéristiques spécifiques en terme de forme de mains, regard et vocalisations. De plus, une attention particulière a été apportée à l’étude des préférences manuelles dans le but de mieux comprendre le développement de la spécialisation hémisphérique gauche pour les comportements communicatifs. Nos résultats ont révélé des relations complexes entre le langage, les gestes communicatifs et les activités de manipulation, qui dépendent de la fonction des gestes (i.e., pointage impératif versus déclaratif) et des étapes spécifiques de l’acquisition du langage. Les gestes déclaratifs sont plus étroitement associés au développement de la parole que les gestes impératifs, au-moins avant la période d’explosion lexicale. De plus, la comparaison des patterns de préférence manuelle chez l’enfant et l’adulte a montré une plus grande proximité pour les gestes que pour la manipulation d’objet. L’asymétrie manuelle droite pour les gestes communicatifs est ainsi établie à des stades précoces, ce qui suggère un rôle primordial des gestes dans la spécialisation hémisphérique.Finalement, nos résultats ont mis en évidence l’existence d’un système de communication dans l’hémisphère cérébral gauche contrôlant à la fois la communication gestuelle et verbale, qui pourrait avoir une origine phylogénétique ancienne (e.g., Corballis, 2010). Par conséquent, le présent travail peut améliorer notre compréhension des origines du langage, y compris des mécanismes de la spécialisation cérébrale pour les comportements communicatifs. / Even though children’s early use of communicative gestures is recognized as being closely related to language development (e.g., Colonnesi et al., 2010), the nature of speech–gestures links still needs to be clarified. This dissertation aims to investigate the production of pointing gestures during development to determine whether the predictive and facilitative relationship between gestures and language acquisition involves specific functions of pointing, in association with specific features in terms of hand shape, gaze and accompanying vocalizations. Moreover, special attention was paid to the study of hand preferences in order to better understand the development of left hemisphere specialization for communicative behaviors. Our results revealed complex relationships between language, communicative gestures and manipulative activities depending on the function of gestures (i.e., imperative versus declarative pointing) as well as on specific stages of language acquisition. Declarative gestures were found to be more closely associated with speech development than imperative gestures, at least before the lexical spurt period. In addition, the comparison of hand-preference patterns in adults and infants showed stronger similarity for gestures than for object manipulation. The right-sided asymmetry for communicative gestures is thus established in early stages, which suggests a primary role of gestures in hemispheric specialization.Finally, our findings have highlighted the existence of a left-lateralized communication system controlling both gestural and vocal communication, which has been suggested to have a deep phylogenetic origin (e.g., Corballis, 2010). Therefore, the present work may improve current understanding of the evolutionary roots of language, including the mechanisms of cerebral specialization for communicative behaviors.

Les objectifs de ce programme de recherche étaient, d’une part, d’apporter une compréhension critique des techniques non-invasives utilisées dans la localisation et/ou la latéralisation des aires langagières et mnésiques en tenant compte de leurs avantages, de leurs limites propres ainsi que de leur pertinence dans un contexte clinique. D’autre part, d’approfondir notre compréhension de l’organisation cérébrale langagière auprès d’une population de sujets ayant une agénésie du corps calleux en utilisant un protocole de neuroimagerie. Afin de répondre à notre premier objectif, une revue critique de la littérature des méthodes de neuroimagerie utilisées pour la latéralisation et la localisation des aires cérébrales sous-tendant le traitement langagier et mnésique dans le contexte du bilan préchirurgical des patients épileptiques a été effectuée. Ce travail a permis d’identifier que certaines de ces nouvelles techniques et plus spécialement leur combinaison, montrent un potentiel réel dans ce contexte clinique. Cette recherche a également permis de mettre en lumière que ces méthodes ont encore un grand besoin d’être raffinées et standardisées avant d’être utilisées comme remplacement au test à l’amobarbital intracarotidien dans un contexte clinique sécuritaire. Afin de répondre à notre deuxième objectif, nous avons exploré les patrons de latéralisation du langage auprès de six sujets acalleux en utilisant un protocle d’imagerie par résonance magnétique fonctionnelle (IRMf). Les résultats indiquent que les individus ayant une agénésie du corps calleux montrent un patron d’activation cérébrale tout aussi latéralisé que nos deux groupes contrôles (QI apparié et QI élevé) lors du traitement du langage réceptif. Les sujets ayant une agénésie du corps calleux montrent également un patron de latéralisation comparable à leur groupe contrôle apparié pour le QI pour la tâche de langage expressif. Lorsque l’on compare les sujets ayant une agénésie du corps calleux au groupe contrôle de QI élevé, ces derniers montrent une latéralisation moins marquée uniquement pour la région frontale lors de la tâche de langage expressif. En conclusion, les résultats de cette étude ne supportent pas l’affirmation que le corps calleux jouerait un rôle inhibiteur essentiel afin de permettre un développement normal de la latéralisation hémisphérique pour le langage. / The goals of this research program were, on the one end, to bring a critical understanding of the non invasive techniques used for the localisation and lateralisation of language and memory functions taking into account their respective advantages, limits and relevance in a patient care context. On the other end, we wanted to deepen our understanding of cerebral language organization in the context of the study of acallosal subjects. To meet our first objective, we performed a comprehensive review of the litterature of neuroimaging methods used in language and memory lateralisation and localisation in the context of presurgical assessment of epileptic patients. In this work, we pointed out that some of these new methodologies and moreover their combinations show an interesting potential for the use in a clinical context. We also pointed out that these methods still need to be refined and standardised before replacing the intracarotid amobarbital test in a safe clinical setting. To meet our second objective, we explored patterns of language lateralization in six individuals with callosal agenesis using a functional magnetic resonance imaging (fMRI) protocol. No differences were found between language lateralization of subjects with agenesis of the corpus callosum and the control groups (High-IQ and IQ-matched) in the receptive speech task. However, for expressive speech, the groups differed with respect to frontal activations, with the acallosal participants showing a more bilateral pattern of activation than the high-IQ participants only. No differences were found in themporal regions. Overall, these results indicate that the corpus callosum is not essential for the establishment of lateralized language functions.