The left hemisphere (LH) is accepted as the dominant hemisphere for language processing. There is also evidence confirming the language processing abilities of the right hemisphere (RH), particularly its lexical-semantic processing potential (Chiarello, 1988; Joanette, Goulet, & Hannequin, 1990). The capacity of the RH for language processing is significant to the investigation of language processing following LH lesions. However, the precise neurocognitive mechanisms underlying language processing following lesion remain to be fully elucidated. Subsequently, the overall aim for this thesis is to investigate hemispheric contributions to semantic processing following unilateral lesions, and to explore the significance of the contribution made by the RH. In order to achieve this overall aim, the current thesis firstly explores the hemispheric contributions made to lexical-semantic processing for healthy adults, and then shifts focus to explore the changes in hemispheric processing for participants with unilateral lesions (LH and RH). Comparisons of hemispheric activation between these groups will clarify the underlying hemispheric mechanisms that facilitate language processing following unilateral lesion. This thesis includes four complementary investigations of hemispheric contributions to semantic processing. The first study combined divided visual field (DVF) priming with event-related potentials (ERPs), in order to investigate controlled hemispheric semantic priming for young healthy adults. Two experiments were employed for a between subjects comparison of time-course differences (stimulus onset asynchrony, or SOA, varied between experiments) in hemispheric activation of associated and nonassociated category members. Continuous electroencephalograms were recorded throughout the priming task for each participant, and later analysed with reference to relevant ERP components (N400 and Late Positive Complex). Bilateral N400 priming was revealed for associated category members at both the short and long SOA. There was no significant N400 priming for the nonassociated category member condition. The examination of hemispheric priming of associated and nonassociated category member stimuli over the same time-course was continued in the second study for participants with unilateral LH lesions and matched controls. The second investigation aimed to determine the impact of unilateral LH lesions on controlled hemispheric semantic priming, utilising the DVF priming paradigm with participants following unilateral lesions. This study also aimed to explore associations between hemispheric activation during the online priming task and offline comprehension abilities. Differences in priming were observed between the LH lesion group and the control group, with participants in the LH lesion group requiring the association relationship to elicit priming. Priming also varied for participants as a function of their offline comprehension abilities, with RH priming associated with higher offline scores. The third investigation continued the exploration of hemispheric semantic activation following LH lesion, examining the impact of a LH lesion on interhemispheric control mechanisms, and the modification of hemispheric processing capacities with and without dominant hemisphere control. This investigation again utilised DVF priming with associated and nonassociated category member stimuli, in conjunction with the dual task paradigm. The dual task paradigm is designed to overload one hemisphere’s processing resources in order to remove interhemispheric suppression. Findings indicate that following LH lesions, the RH’s contribution is enhanced under conditions that are designed to overload the LH. The final study shifts from the investigation of participants with LH lesions to the impact of a RH lesion. This exploration of controlled hemispheric semantic priming following RH lesion sought to increase our understanding of the underlying mechanisms for semantic processing following unilateral lesion. The RH’s role in lexical-semantic processing has been documented consistently over approximately the last twenty years, however, there remains limited direct investigation of a RH lesion’s impact on contributions to semantic processing. A single case investigation utilised the same experimental procedure as the second study described. Findings suggest a similar activation pattern between the individual with RH lesion and the control participants, with both exhibiting bilateral activation of the associated and nonassociated category member stimuli. However, a subtle difference was found between the activation of the individual with RH lesion and that of the control group, with the individual with a RH lesion showing increased strategic processing difficulties at the longer SOA. Overall, the current thesis demonstrates the importance of the RH for efficient strategic semantic processing for both healthy adults, and people with unilateral lesions. In addition, this thesis concludes that following a LH lesion, the RH contribution to controlled semantic processing may be associated with successful comprehension, and that RH contributions may be improved with the addition of a secondary task designed to overload LH processing. The present thesis provides evidence to support the use of the DVF priming paradigm in the investigation of hemispheric contributions to semantic processing following unilateral lesion. It is anticipated that these findings will improve the current understanding of the underlying hemispheric contributions to lexical-semantics following a unilateral lesion, and will encourage continuing investigation into the RH’s capacity to impact language recovery.

The left hemisphere (LH) is accepted as the dominant hemisphere for language processing. There is also evidence confirming the language processing abilities of the right hemisphere (RH), particularly its lexical-semantic processing potential (Chiarello, 1988; Joanette, Goulet, & Hannequin, 1990). The capacity of the RH for language processing is significant to the investigation of language processing following LH lesions. However, the precise neurocognitive mechanisms underlying language processing following lesion remain to be fully elucidated. Subsequently, the overall aim for this thesis is to investigate hemispheric contributions to semantic processing following unilateral lesions, and to explore the significance of the contribution made by the RH. In order to achieve this overall aim, the current thesis firstly explores the hemispheric contributions made to lexical-semantic processing for healthy adults, and then shifts focus to explore the changes in hemispheric processing for participants with unilateral lesions (LH and RH). Comparisons of hemispheric activation between these groups will clarify the underlying hemispheric mechanisms that facilitate language processing following unilateral lesion. This thesis includes four complementary investigations of hemispheric contributions to semantic processing. The first study combined divided visual field (DVF) priming with event-related potentials (ERPs), in order to investigate controlled hemispheric semantic priming for young healthy adults. Two experiments were employed for a between subjects comparison of time-course differences (stimulus onset asynchrony, or SOA, varied between experiments) in hemispheric activation of associated and nonassociated category members. Continuous electroencephalograms were recorded throughout the priming task for each participant, and later analysed with reference to relevant ERP components (N400 and Late Positive Complex). Bilateral N400 priming was revealed for associated category members at both the short and long SOA. There was no significant N400 priming for the nonassociated category member condition. The examination of hemispheric priming of associated and nonassociated category member stimuli over the same time-course was continued in the second study for participants with unilateral LH lesions and matched controls. The second investigation aimed to determine the impact of unilateral LH lesions on controlled hemispheric semantic priming, utilising the DVF priming paradigm with participants following unilateral lesions. This study also aimed to explore associations between hemispheric activation during the online priming task and offline comprehension abilities. Differences in priming were observed between the LH lesion group and the control group, with participants in the LH lesion group requiring the association relationship to elicit priming. Priming also varied for participants as a function of their offline comprehension abilities, with RH priming associated with higher offline scores. The third investigation continued the exploration of hemispheric semantic activation following LH lesion, examining the impact of a LH lesion on interhemispheric control mechanisms, and the modification of hemispheric processing capacities with and without dominant hemisphere control. This investigation again utilised DVF priming with associated and nonassociated category member stimuli, in conjunction with the dual task paradigm. The dual task paradigm is designed to overload one hemisphere’s processing resources in order to remove interhemispheric suppression. Findings indicate that following LH lesions, the RH’s contribution is enhanced under conditions that are designed to overload the LH. The final study shifts from the investigation of participants with LH lesions to the impact of a RH lesion. This exploration of controlled hemispheric semantic priming following RH lesion sought to increase our understanding of the underlying mechanisms for semantic processing following unilateral lesion. The RH’s role in lexical-semantic processing has been documented consistently over approximately the last twenty years, however, there remains limited direct investigation of a RH lesion’s impact on contributions to semantic processing. A single case investigation utilised the same experimental procedure as the second study described. Findings suggest a similar activation pattern between the individual with RH lesion and the control participants, with both exhibiting bilateral activation of the associated and nonassociated category member stimuli. However, a subtle difference was found between the activation of the individual with RH lesion and that of the control group, with the individual with a RH lesion showing increased strategic processing difficulties at the longer SOA. Overall, the current thesis demonstrates the importance of the RH for efficient strategic semantic processing for both healthy adults, and people with unilateral lesions. In addition, this thesis concludes that following a LH lesion, the RH contribution to controlled semantic processing may be associated with successful comprehension, and that RH contributions may be improved with the addition of a secondary task designed to overload LH processing. The present thesis provides evidence to support the use of the DVF priming paradigm in the investigation of hemispheric contributions to semantic processing following unilateral lesion. It is anticipated that these findings will improve the current understanding of the underlying hemispheric contributions to lexical-semantics following a unilateral lesion, and will encourage continuing investigation into the RH’s capacity to impact language recovery.

The left hemisphere (LH) is accepted as the dominant hemisphere for language processing. There is also evidence confirming the language processing abilities of the right hemisphere (RH), particularly its lexical-semantic processing potential (Chiarello, 1988; Joanette, Goulet, & Hannequin, 1990). The capacity of the RH for language processing is significant to the investigation of language processing following LH lesions. However, the precise neurocognitive mechanisms underlying language processing following lesion remain to be fully elucidated. Subsequently, the overall aim for this thesis is to investigate hemispheric contributions to semantic processing following unilateral lesions, and to explore the significance of the contribution made by the RH. In order to achieve this overall aim, the current thesis firstly explores the hemispheric contributions made to lexical-semantic processing for healthy adults, and then shifts focus to explore the changes in hemispheric processing for participants with unilateral lesions (LH and RH). Comparisons of hemispheric activation between these groups will clarify the underlying hemispheric mechanisms that facilitate language processing following unilateral lesion. This thesis includes four complementary investigations of hemispheric contributions to semantic processing. The first study combined divided visual field (DVF) priming with event-related potentials (ERPs), in order to investigate controlled hemispheric semantic priming for young healthy adults. Two experiments were employed for a between subjects comparison of time-course differences (stimulus onset asynchrony, or SOA, varied between experiments) in hemispheric activation of associated and nonassociated category members. Continuous electroencephalograms were recorded throughout the priming task for each participant, and later analysed with reference to relevant ERP components (N400 and Late Positive Complex). Bilateral N400 priming was revealed for associated category members at both the short and long SOA. There was no significant N400 priming for the nonassociated category member condition. The examination of hemispheric priming of associated and nonassociated category member stimuli over the same time-course was continued in the second study for participants with unilateral LH lesions and matched controls. The second investigation aimed to determine the impact of unilateral LH lesions on controlled hemispheric semantic priming, utilising the DVF priming paradigm with participants following unilateral lesions. This study also aimed to explore associations between hemispheric activation during the online priming task and offline comprehension abilities. Differences in priming were observed between the LH lesion group and the control group, with participants in the LH lesion group requiring the association relationship to elicit priming. Priming also varied for participants as a function of their offline comprehension abilities, with RH priming associated with higher offline scores. The third investigation continued the exploration of hemispheric semantic activation following LH lesion, examining the impact of a LH lesion on interhemispheric control mechanisms, and the modification of hemispheric processing capacities with and without dominant hemisphere control. This investigation again utilised DVF priming with associated and nonassociated category member stimuli, in conjunction with the dual task paradigm. The dual task paradigm is designed to overload one hemisphere’s processing resources in order to remove interhemispheric suppression. Findings indicate that following LH lesions, the RH’s contribution is enhanced under conditions that are designed to overload the LH. The final study shifts from the investigation of participants with LH lesions to the impact of a RH lesion. This exploration of controlled hemispheric semantic priming following RH lesion sought to increase our understanding of the underlying mechanisms for semantic processing following unilateral lesion. The RH’s role in lexical-semantic processing has been documented consistently over approximately the last twenty years, however, there remains limited direct investigation of a RH lesion’s impact on contributions to semantic processing. A single case investigation utilised the same experimental procedure as the second study described. Findings suggest a similar activation pattern between the individual with RH lesion and the control participants, with both exhibiting bilateral activation of the associated and nonassociated category member stimuli. However, a subtle difference was found between the activation of the individual with RH lesion and that of the control group, with the individual with a RH lesion showing increased strategic processing difficulties at the longer SOA. Overall, the current thesis demonstrates the importance of the RH for efficient strategic semantic processing for both healthy adults, and people with unilateral lesions. In addition, this thesis concludes that following a LH lesion, the RH contribution to controlled semantic processing may be associated with successful comprehension, and that RH contributions may be improved with the addition of a secondary task designed to overload LH processing. The present thesis provides evidence to support the use of the DVF priming paradigm in the investigation of hemispheric contributions to semantic processing following unilateral lesion. It is anticipated that these findings will improve the current understanding of the underlying hemispheric contributions to lexical-semantics following a unilateral lesion, and will encourage continuing investigation into the RH’s capacity to impact language recovery.

Esta pesquisa tem como objetivo central a identificação e análise dos principais atores e temas envolvidos na internacionalização do conflito armado na Colômbia. Este estudo entende por internacionalização a participação de atores estrangeiros na formulação e/ou implementação das tentativas de resolução do referido conflito. O recorte temporal pertinente aos propósitos da pesquisa estende-se do Governo César Gaviria (1990-1994) ao final do primeiro governo de Álvaro Uribe (2002-2006), na medida em que, no período anterior, não era possível observar um envolvimento externo considerável nos processos de paz na Colômbia. Os atores selecionados para uma análise mais atenta foram: EUA e OEA, cujas agendas correspondem à proposta hemisférica predominante; e UE e ONU, as quais representam as iniciativas globais voltadas à resolução do conflito. A principal conclusão deste estudo incide sobre o agrupamento das propostas internacionais em torno desses dois pólos: hemisféricas (das quais os EUA constituem o principal expoente) e globais (que têm na UE o seu ponto focal). A primeira é dotada de vultosos recursos, apresenta um caráter marcadamente militar e encontra na erradicação das drogas e no confronto às guerrilhas as suas principais estratégias. Por outro lado, o traço preponderante da segunda é a ênfase nos direitos humanos, na ajuda humanitária e na negociação com as guerrilhas. A proposta emergente do pólo europeu não foi capaz de oferecer um contra-peso à intervenção estadunidense, tanto em termos de recursos financeiros, como de fatores geopolíticos. Assim, a principal conclusão desta pesquisa é que a internacionalização do conflito armado não se manifesta de forma homogênea: embora a participação dos atores estrangeiros tenha ocorrido no âmbito global, as iniciativas hemisféricas são predominantes, especialmente se analisarmos as preferências do governo colombiano. / This study aims to identify and analyze the main actors and themes related to the Colombian armed conflict internationalization. It understands internationalization as the participation of foreign players in the designing and implementation of programs regarding the resolution of the conflict. The period of interest to this study dates back to the government César Gaviria (1990-1994) until the end of the first Álvaro Uribe administration, since there was no considerable external participation on Colombia peace processes previously. The selected players for a more detailed approach were: US and OAS, whose agendas correspond to the predominant proposal in the hemisphere; and EU and UN, which represent the global initiatives towards the conflict resolution. The main conclusion of this study is related to the concentration of international proposals around these poles: hemispheric (whose main exponent is the US) and global (concentrated on EU). The first involves a huge amount of resources, presents a markedly military aspect and privileges the illicit crops eradication and confrontation against guerrillas as strategies. On the other hand, the dominant characteristic of the second is the emphasis on human rights, humanitarian aid and the negotiation with the guerrillas. The proposal that emerged from Europe was not able to offer compensation to American intervention in terms of financial resources and geopolitical factors. Therefore, the main conclusion of this study is that the internationalization of the armed conflict is not homogeneous throughout the world: the participation of external actors is global, but the hemispherical initiatives are predominant, especially if we consider Colombian governments preferences.

The purpose of this thesis focused on a literature curriculum designed to improve reading comprehension through the stimulation of the right hemisphere of the brain. A case study of this curriculum development effort involved a third-grade student from a local public 2 school. He was a part-time Specific Learning Disability student with weaknesses in visual organization, visual concentration, and reading comprehension. A time span of six weeks was dedicated to increasing the child's reading comprehension within a literature framework through the use of right-brain stimulants, specifically, color and visualization. The Gates-MacGinitie Reading Test, Level C, administered at the conclusion of the instructional sessions, and teacher observation provided the evaluation of the curriculum. Results of the study proved inconclusive. Further field study was recommended.

Learner’s processing styles may play a vital role in their approach to learning, more specifically; the ability to make inferences plays an important role in all areas of language and learning and may contribute to difficulties learners are experiencing at school. It is therefore that the research was directed at investigating a possible relationship between the left hemispheric analytical and right hemispheric holistic processing styles and the types of errors inferential versus literal, made in reading comprehension tasks. The hemispheric processing styles were operationalised as the approach taken to the Rey- Osterreith Complex Figure (ROCF) and the types of errors made on the Stanford Diagnostic Reading Test (SDRT) across two levels of educational development. The sample consisted of grade 4 and grade 10 model C learners from the same schooling district. The data obtained from both assessments were subjected to correlation analyses, chi squared tests, analyses of variances (ANOVAs) and logistic regressions. Finally the results and associative conclusions indicated that there were only modest positive relationships between the predominant hemispheric processing styles and the error types on reading comprehension tasks and the demographics of the learners were the main contributors and accounted for the results discovered in the study as opposed to general hemispheric processing. Thus there is a need to understand the unique dynamics within the country and to explore alternatives to teaching practices to account for the variations evident in the classrooms.

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.

Le modèle computo-fonctionnel de la vision de haut niveau de Kosslyn et Koenig (1992) repose sur la dissociation entre la reconnaissance et le traitement spatial de la scène visuelle. En 1987, Kosslyn postula l’existence de deux processus pour le traitement des relations spatiales : un processus catégoriel qui calcule les positions relatives des objets et un processus coordonné qui calcule la distance entre les objets. Des études utilisant le paradigme de présentation en champ visuel divisé ont mis en évidence que l’hémisphère gauche sous-tendrait un traitement catégoriel ; l’hémisphère droit sous-tendrait un traitement coordonné. Cette interaction semblerait valider la dichotomie des deux types de processus.Une revue de la littérature pluridisciplinaire a été menée afin de savoir si ce fait est suffisant pour rejeter l’hypothèse d’un processus unique pour les traitements catégoriels et coordonnés. Entre autres, plusieurs études ont observé un effet de pratique au cours de la réalisation de jugements coordonnés : une diminution de l’intervention de l’hémisphère droit au profit d’une prise en charge progressive de l’hémisphère gauche. De plus, l’avantage de l’hémisphère gauche pour le traitement catégoriel a été rarement observé.Une série de cinq expériences comportementales ont été conduites pour vérifier certains biais expérimentaux qui pourraient expliquer les différences hémisphériques et l’effet de pratique observés. Nos résultats nous ont permis d’avancer des hypothèses axées sur la communication entre les hémisphères et sur un lien entre les processus catégoriels et coordonnés. Une critique du paradigme de présentation en champ visuel divisé et différents modèles d’interaction hémisphérique ont été présentés. Trois expériences ont été menées, afin d’évaluer l’impact des communications hémisphériques dans le traitement des relations spatiales. A la lumière de nos résultats, la dichotomie des processus catégoriels et coordonnés a été discutée. / The computational-functional conception of high-level processing of vision in Kosslyn and Koenig (1992) relies on dissociation between object recognition and spatial processing. In 1987, Kosslyn postulated that two different processes compute spatial-relations: categorical process computes relative position of objects and coordinate process computes the distance between objects. Some studies indicate a left-hemisphere advantage for processing categorical spatial relations and a right-hemisphere advantage for processing coordinate spatial relations. This hemispheric difference is interpreted as an evidence of a dichotomy between these two processes. A pluridisciplinary review was conducted to assure that single process hypothesis is dismissed out. Some studies showed, in a coordinate task, that practice resulted in a decreased right-hemisphere involvement and a concurrent increase in left-hemisphere involvement (i.e., practice effect). Furthermore, the left-hemisphere advantage in categorical was seldom observed. The theoretical aim of the thesis was based on two questions: (1) Are there single or several processes encoding visual spatial relations? (2) How can we interpret this practice effect ?Five experiments were run to verify possible bias which might explain observed hemispheric differences and practice effect. Our results suggested that hemispheric communication might be an important factor in spatial-relation processing.An theoretical investigation of divided visual field paradigm was led and several interhemispheric models were described. Three experiments were conducted to estimate hemispheric communication in spatial-relation process. In the light of our results, separate categorical-coordinate processes hypothesis were discussed.

Le phénomène de Clignement Attentionnel (Attentional Blink, AB), fait référence à une diminution transitoire du rapport exact d’une deuxième cible (C2) si celle-ci est présentée trop tôt après une première cible (C1) lors d’une présentation visuelle sérielle rapide (rapid serial visual presentation, RSVP), et ce, quand les deux cibles doivent être rapportées. Cette étude a examiné l’existence possible d’asymétries hémisphèriques dans le traitement attentionnel ainsi que l’éventualité que la présentation de cibles à deux hémisphères différents puisse diminuer le AB chez des participants neurologiquement sains et l’abolir dans le cas d’un patient callosotomisé. Pour ce faire, nous avons employé un paradigme modifié du AB dans lequel les cibles pouvaient apparaître dans n’importe quelle de quatre RSVP, une dans chaque quadrant du champ visuel, pour permettre des essais dans lesquels les deux cibles puissent être présentées au même hémisphère et d’autres où chaque cible était présentée à un hémisphère différent. Bien que nous n’ayons trouvé aucune diminution de l’effet AB lors de présentation inter-hémisphérique, dans les deux populations à l’étude, le taux de bonnes réponses globales à la deuxième cible était plus élevé quand les cibles étaient présentées à des hémisphères différents. Nous avons également trouvé un avantage de l’hémisphère gauche chez le patient callosotomisé. / The Attentional Blink (AB) refers to a transient impairment in the accurate report of a second target (T2) if it closely follows the presentation of a first target (T1) in a rapid serial visual presentation (RSVP), when both targets must be reported. This study investigated both the possibility of hemispheric asymmetries of attentional processes as well as the possibility that presenting targets to different hemispheres could diminish the AB in neurologically intact participants and abolish it in the case of a split-brain patient. To do so, a modified AB paradigm was used in which targets could appear in any of four simultaneous RSVP streams, one in each quadrant of the visual field, so as to have trials in which both targets were presented to the same hemispheres and trials in which targets were presented to different hemispheres. Although no evidence of a diminished AB was observed by presenting targets to separate hemispheres, in both neurologically intact individuals and the split-brain patient, overall accuracy was higher when targets were presented to separate hemispheres. A left hemisphere advantage was only observed in the split-brain patient.

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.