Résumé : Une coordination appropriée entre les pattes antérieures et postérieures chez les mammifères terrestres est essentielle pour maintenir une stabilité pendant la locomotion quadrupède. Il a été fortement suggéré que les voies propriospinales et le retour sensoriel pourraient jouer un rôle important dans la coordination antéropostérieure. Cependant, les mécanismes neurophysiologiques impliqués dans la coordination entre les membres antérieurs et les membres postérieurs pendant la marche demeurent méconnus. Suite à une lésion partielle de la moelle épinière, plusieurs déficits de la coordination antéropostérieure ont pu être dénotés chez l’animal non-humain et chez l’humain. Malgré tout, les effets d’une lésion partielle sur la coordination antéropostérieure n’ont pas encore été clairement caractérisés. Au regard du nombre considérable de blessés médullaires présentant des troubles de l’équilibre et de la coordination entre les bras et les jambes après avoir récupéré la marche, il semble essentiel de mieux comprendre ces mécanismes. L’objectif du projet était d’offrir une meilleure caractérisation de la coordination antéropostérieure chez le chat intact et suite à une hémisection latérale de la moelle épinière. Pour ce faire, un tapis roulant partitionné transverse permettant de dissocier les vitesses de locomotion entre les pattes antérieures et postérieures a été utilisé. Huit chats implantés chroniquement pour réaliser des enregistrements électromyographiques ont été entrainés dans diverses conditions de locomotion partitionnée et non-partitionnée. Parmi ces 8 chats, 6 ont subi une hémisection latérale du côté droit de la moelle épinière entre la 5ème et la 6ème vertèbre thoracique (T6). Des analyses cinématiques et électromyographiques ont été réalisées chez les chats intacts et 8 semaines après la lésion partielle de la moelle épinière. Les résultats obtenus démontrent que la coordination antéropostérieure est contrôlée par des influences bidirectionnelles et asymétriques entre les pattes antérieures et postérieures. De plus, lorsque la vitesse de locomotion des pattes antérieures était plus élevée que celle des pattes postérieures, une dissociation du rythme était observée avec les pattes antérieures réalisant davantage de pas chez le chat intact. Suite à la lésion, cette dissociation était également observée lors de la locomotion non-partitionnée. Cependant, que ce soit avant ou après la lésion, quand une telle dissociation apparaissait, une nouvelle forme stable de coordination antéropostérieure apparaissait consistant à réaliser deux pas des pattes antérieures pendant un pas des pattes postérieures (coordination 2-1). Finalement, la coordination antéropostérieure pouvait être modulée par l’utilisation du tapis roulant partitionné et une coordination 1-1 pouvait être restaurée suite à la lésion en faisant marcher les pattes postérieures à une vitesse plus élevée. À partir de ces résultats, nous avons proposé un nouveau modèle théorique du contrôle neurophysiologique de la coordination antéropostérieure. Qui plus est, un raffinement des échelles d’évaluation de la récupération locomotrice suite à des lésions de la moelle épinière s’avère indispensable afin d’inclure une caractérisation détaillée de la coordination antéropostérieure. Finalement, d’un point de vue clinique, ces résultats suggèrent que de nouvelles stratégies thérapeutiques basées sur la coordination antéropostérieure pourraient être envisagées afin de renforcer la récupération locomotrice suite à des lésions de la moelle épinière. / Abstract : An appropriate coordination between the forelimbs and the hindlimbs in terrestrial mammals is essential to maintain stability during quadrupedal locomotion. It is thought that propriospinal pathways and sensory feedback contribute to the control of forelimbhindlimb coordination. However, the neurophysiological mechanisms involved in this coordination during locomotion remain poorly defined. After a partial spinal cord injury, several impairments of interlimb coordination have been observed in non-human animal models and human patients. Despite this, the effects of a partial lesion on forelimb-hindlimb coordination have not been clearly characterised. Patients with spinal cord injury have pronounced deficits with their equilibrium and a deficient control of interlimb coordination could be a main contributor. The purpose of these studies was to better characterize forelimb-hindlimb coordination in intact cats and following a lateral hemisection of the spinal cord. A transverse split-belt treadmill was used to independently control the speed of the forelimbs and of the hindlimbs. Eight cats were chronically implanted for e;ectromyography and trained to perform various tied-belt and transverse split-belt locomotor conditions. Among these 8 cats, 6 were hemisected at the 6th thoracic segment of the spinal cord on the right side. Electromyographic and kinematic analyses were performed in the intact state and 8 weeks post-hemisection. The results demonstrate that interlimb coordination is controlled by bidirectional and asymmetrical influences between the forelimbs and the hindlimbs. Moreover, when the forelimbs stepped faster than the hindlimbs, dissociation of the forelimb and hindlimb rhythms occurred, with the forelimbs taking more steps. After the lesion, this dissociation was observed, even during tied-belt locomotion. However, in both intact and injured cats, when such dissociation occurred, a new stable form of forelimb-hindlimb coordination appeared, consisting of two forelimb steps for one hindlimb step (2-1 forelimb-hindlimb coordination). Finally, the transverse split-belt treadmill could modulate forelimb-hindlimb coordination and 1-1 coordination could be restored after the lesion during transverse split-belt locomotion with a faster hindlimb speed. From these results, we propose a theoretical model of the neurophysiological control of interlimb coordination. Moreover, a refinement of performance scales evaluating the locomotor recovery after spinal cord injury is necessary to include a detailed characterisation of interlimb coordination. Finally, from a clinical perspective, these results suggest that new therapeutic strategies based on interlimb coordination could be used to strengthen locomotor recovery after spinal cord injuries.

À ce jour, le rôle des oscillations bêta n’a pas encore été clairement établi. Des travaux récents ont montré que l’activité bêta pendant la préparation du mouvement et celle suivant son exécution sont différemment modulées par les erreurs de mouvements. L’objectif du présent travail a été double : premièrement, déterminer si les modulations de puissance bêta pré- et post-mouvement recrutent des substrats cérébraux différents, deuxièmement, mieux cerner la nature des processus neuronaux reflétés. Grâce à une approche par analyse en composantes indépendantes, nous suggérons fortement que les réponses oscillatoires, aux erreurs cinématiques, observées avant et après le mouvement sont sous-tendues par des structures distinctes, respectivement clairement latéralisées et médiales. De plus, en contrastant différentes tâches motrices, nous montrons que ni l’une ni l’autre des deux activités bêta ne reflètent des mécanismes en lien direct avec les sorties motrices. / The role of beta oscillations has not been clearly established yet. Recent work has shown that the beta activities observed during the preparation phase and after the movement are differently affected by movement errors. The aim of this thesis was twofold: first, to determine whether or not the pre- and post-movement beta power modulations recruit common neural substrates; second, to better understand the nature of the reflected neural processes. Using an independent component analysis approach, we strongly suggest that oscillatory responses to kinematic errors, observed before and after movement, are underpinned by distinct neural structures, respectively clearly lateralized and medial. Moreover, by contrasting different motor tasks, we show that neither of the two beta activities reflects mechanisms directly related to the output of the motor command.

Orientador: Ana Maria Pellegrini / Banca: Cynthia Yukiko Hiraga / Banca: José Angelo Barela / Resumo: A coordenação intermembros é exigida em inúmeras atividades motoras. Nestas atividades, os indivíduos precisam coordenar muitos componentes do corpo, mantendo relações entre eles e destes com o ambiente. Em um sistema dinâmico complexo, as relações entre as partes do sistema limitam ou influenciam o comportamento de outras partes, levando à emergência de padrões de coordenação. Crianças com Transtorno do Desenvolvimento da Coordenação (TDC) têm sido caracterizadas por apresentarem dificuldade em coordenar ritmicamente as partes do corpo em padrões específicos de coordenação intermembros. O presente estudo investigou a emergência e a estabilidade de padrões motores de crianças com TDC em uma tarefa rítmica de coordenação intermembros, analisando suas capacidades de sincronizar os deslocamentos dos membros superiores e inferiores em diferentes superfícies de apoio. Doze crianças com Desenvolvimento Típico (DT) e 12 crianças com TDC realizaram a tarefa de saltar e bater palma, durante 15 segundos, em duas superfícies: rígida (chão) e elástica (mini-trampolim). Foi solicitado à criança saltar e bater palma em quatro condições de coordenação: (i) de livre escolha do participante - Livre; (ii) batendo palma toda vez que os pés tocavam a superfície de apoio - Palma em Baixo; (iii) batendo palma toda vez que o corpo alcançava a máxima altura do salto - Palma em Cima; e (iv) batendo palma toda vez que os pés tocavam a superfície de apoio e toda vez que o corpo alcançava a máxima altura do salto - Duas Palmas. Quando a tarefa foi executada na condição Livre, os resultados mostraram que o padrão emergente das crianças com TDC foi diferente e mais variável na superfície mini-trampolim comparado com o das crianças com DT e com o delas mesmas na superfície chão. Além disso, na condição Palma em Baixo e Palma em Cima, as crianças... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Interlimb coordination is required in many motor activities. To perform these activities, people have to coordinate all body segments at the same time, keeping a relationship between segments and with the environment. In a complex dynamic system, the relationships between its parts limit or influence the behavior of other parts, so coordination patterns emerge. Children with Developmental Coordination Disorder (DCD) have been characterized by showing difficulty in rhythmically coordinate body segments, in specific interlimb coordination patterns. The purpose of this study was to investigate the emergency and stability of coordination patterns in children with DCD when they perform a rhythmic interlimb coordination task, analyzing their abilities to synchronize the movements of upper and lower limbs in two different surfaces. Twelve children with Typical Development (TD) and 12 children with DCD performed a jumping and clapping task during 15 seconds in two surfaces: rigid (on the floor) and elastic (on the mini-tramp). Children were required to clap while jumping (i) in their chosen pattern - Free; (ii) when the feet touched on the surface - Clapping-surface; (iii) when the body reached the maximum jumping height - Clapping-jumping; and (iv) when the feet touched the surface and when the body reached the maximum jumping height - Clapping-both. For the Free condition, the results showed that the DCD children emergent pattern was different and more variable on the mini-tramp than on the floor as compared with TD children coordination pattern. Furthermore, children with DCD were more variable in Clapping-surface and Clapping-jumping conditions compared with TD children. Clapping-jumping condition, characterized by relative phase of 180°, was more difficult for both DCD and TD children to perform than Clapping-surface condition, characterized by relative phase... (Complete abstract click electronic access below) / Mestre

Rhythmic arm cycling suppresses the soleus H-reflex amplitude in stationary legs in neurologically intact (NI) participants. It has been suggested that interlimb pathways connecting cervical and lumbosacral spinal cord are responsible for modulating the reflex excitability. After stroke, stretch reflex and its electrical analogue the H-reflex become hyperactive. The purpose of this study was to examine the effect of arm cycling on the H-reflex amplitude in the stationary legs after stroke. It was hypothesized that rhythmic arm movement would suppress the H-reflex amplitudes in the Iegs after stroke. Sixteen stroke participants performed bilateral arm cycling at 1Hz and at the highest frequency possible they could maintain. Additionally, thirteen age-matched neurologically intact individuals participated as a control group. Tibial nerves were stimulated to evoke H-reflexes simultaneously in both legs. M-wave, H-reflex (M-H) recruitment curves (RC) were collected during arm cycling and with arms stationary. Four variables (i.e.. M-H slope, H at threshold. Hmax, and 50% Hmax] obtained from the ascending limb of the M-H RC were compared across conditions. Results showed that the general effects of arm cycling in suppressing H-reflex size are preserved after stroke. However, effects after stroke were limited in that arm cycling did not affect the whole recruitment curve similarly, as it does in the NI population. Overall the results suggest that incorporation of rhythmic arm movement in rehabilitation paradigms after stroke might be helpful in suppression of hyperactive reflexes in the legs and therefore assist in locomotion.

Made available in DSpace on 2016-06-02T20:19:18Z (GMT). No. of bitstreams: 1 4366.pdf: 1667152 bytes, checksum: e2c5f2da90a5571724bcc0550299f17d (MD5) Previous issue date: 2012-02-29 / Financiadora de Estudos e Projetos / Research has shown that bimanual actions are demonstrative of the functional brain development; thus it is relevant to investigate how interlimb coordination develops in typically-developing infants, as well as in infants with impaired brain organization, such as in the presence of Down syndrome (DS). Objectives: The aims of this study were as follows: 1) to study the development of interlimb coordination in typically-developing infants (TD) and in infants with DS while reaching and grasping objects with different sizes; and 2) to investigate changes in the interlimb relations during the stages after reaching emergence. Methods: Reaching movements performed by 8 TD infants and 7 infants with DS were monthly recorded between the ages of 4 and 8 months. The frequency of categories used during movement initiation, object touching and grasping; the frequency of reaching and the contribution of each arm were calculated. The effects of object size and of the time after reaching onset were analyzed in intra- and inter-group comparisons. Results: TD infants were able to change the configurations used in the movement initiation, object touching and grasping; their interlimb coordination changed from synchronic reaches to asynchrony or unimanual trajectories, based on object properties. Infants with DS only changed their grasping configurations; the strategies they used were not optimally adjusted to object properties; difficulties to grasp the objects were also evident. Conclusions: With the experience in reaching, interlimb coordination in TD infants is increasingly modulated by object properties in an anticipatory way. Infants with DS seem to need a longer time to use sensory information and to modulate reaching and grasping configurations. / Ações bimanuais refletem o desenvolvimento funcional de áreas cerebrais, assim, é necessário compreender o desenvolvimento da coordenação intermembros em lactentes típicos (LT) e com alterações na organização cerebral, como na síndrome de Down (SD). OBJETIVO: Estudar o desenvolvimento da coordenação intermembros em LT e com SD ao alcançar e apreender objetos distintos e identificar se há mudanças nas relações intermembros nos períodos após a aquisição do alcance. MÉTODOS: Oito LT e sete lactentes com SD com idade de 4 a 8 meses foram posicionados em uma cadeira infantil e objetos grandes e pequenos foram apresentados por 1 minuto cada. Foi calculada a frequência das variáveis categoriais adotadas no início e trajetória, toque e apreensão do objeto. O efeito do tamanho dos objetos e do tempo após a aquisição do alcance foi analisado nas comparações intra e entre grupos. RESULTADOS: LT mudaram as configurações de início, toque e apreensão do objeto nos períodos após a aquisição do alcance, evoluindo de movimentos sincrônicos para trajetórias assincrônicas ou unimanuais, atendendo às propriedades dos objetos. Lactentes com SD mudaram apenas as configurações de apreensão, apresentando estratégias menos ajustadas aos objetos e dificuldades para apreender os mesmos. CONCLUSÃO: Ao longo da experiência de alcançar, a coordenação intermembros em LT é modificada e progressivamente modulada pelas propriedades dos objetos de maneira antecipatória. Lactentes com SD parecem necessitar de mais tempo para utilizar informações sensoriais e modificar configurações do alcance e apreensão.

Made available in DSpace on 2014-06-11T19:22:52Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-04-17Bitstream added on 2014-06-13T19:08:25Z : No. of bitstreams: 1 ferracioli_mc_me_rcla.pdf: 395950 bytes, checksum: 238b3a5cfad916ec4fe2d5b841ccbae2 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A coordenação intermembros é exigida em inúmeras atividades motoras. Nestas atividades, os indivíduos precisam coordenar muitos componentes do corpo, mantendo relações entre eles e destes com o ambiente. Em um sistema dinâmico complexo, as relações entre as partes do sistema limitam ou influenciam o comportamento de outras partes, levando à emergência de padrões de coordenação. Crianças com Transtorno do Desenvolvimento da Coordenação (TDC) têm sido caracterizadas por apresentarem dificuldade em coordenar ritmicamente as partes do corpo em padrões específicos de coordenação intermembros. O presente estudo investigou a emergência e a estabilidade de padrões motores de crianças com TDC em uma tarefa rítmica de coordenação intermembros, analisando suas capacidades de sincronizar os deslocamentos dos membros superiores e inferiores em diferentes superfícies de apoio. Doze crianças com Desenvolvimento Típico (DT) e 12 crianças com TDC realizaram a tarefa de saltar e bater palma, durante 15 segundos, em duas superfícies: rígida (chão) e elástica (mini-trampolim). Foi solicitado à criança saltar e bater palma em quatro condições de coordenação: (i) de livre escolha do participante – Livre; (ii) batendo palma toda vez que os pés tocavam a superfície de apoio – Palma em Baixo; (iii) batendo palma toda vez que o corpo alcançava a máxima altura do salto – Palma em Cima; e (iv) batendo palma toda vez que os pés tocavam a superfície de apoio e toda vez que o corpo alcançava a máxima altura do salto – Duas Palmas. Quando a tarefa foi executada na condição Livre, os resultados mostraram que o padrão emergente das crianças com TDC foi diferente e mais variável na superfície mini-trampolim comparado com o das crianças com DT e com o delas mesmas na superfície chão. Além disso, na condição Palma em Baixo e Palma em Cima, as crianças... / Interlimb coordination is required in many motor activities. To perform these activities, people have to coordinate all body segments at the same time, keeping a relationship between segments and with the environment. In a complex dynamic system, the relationships between its parts limit or influence the behavior of other parts, so coordination patterns emerge. Children with Developmental Coordination Disorder (DCD) have been characterized by showing difficulty in rhythmically coordinate body segments, in specific interlimb coordination patterns. The purpose of this study was to investigate the emergency and stability of coordination patterns in children with DCD when they perform a rhythmic interlimb coordination task, analyzing their abilities to synchronize the movements of upper and lower limbs in two different surfaces. Twelve children with Typical Development (TD) and 12 children with DCD performed a jumping and clapping task during 15 seconds in two surfaces: rigid (on the floor) and elastic (on the mini-tramp). Children were required to clap while jumping (i) in their chosen pattern - Free; (ii) when the feet touched on the surface - Clapping-surface; (iii) when the body reached the maximum jumping height - Clapping-jumping; and (iv) when the feet touched the surface and when the body reached the maximum jumping height - Clapping-both. For the Free condition, the results showed that the DCD children emergent pattern was different and more variable on the mini-tramp than on the floor as compared with TD children coordination pattern. Furthermore, children with DCD were more variable in Clapping-surface and Clapping-jumping conditions compared with TD children. Clapping-jumping condition, characterized by relative phase of 180°, was more difficult for both DCD and TD children to perform than Clapping-surface condition, characterized by relative phase... (Complete abstract click electronic access below)

La vision fournit des informations essentielles sur la surface de marche, ainsi que sur la taille, la forme et la position d’obstacles potentiels dans notre environnement. Dans le cas d’un prédateur, la vision fournit également des informations sur la vitesse d’une proie potentielle. Les mécanismes neuronaux impliqués dans l’exécution des modifications de la marche sous guidage visuel sont relativement bien connus, mais ceux impliqués dans la planification de ces modifications de la marche sont peu étudiés. Le cortex pariétal postérieur (CPP) semble être un candidat approprié si l’on considère les propriétés du CPP lors des mouvements d’atteinte vers une cible. Le but des présents travaux est de déterminer la contribution du CPP au contrôle de la locomotion sous guidage visuel. La première étude présentée dans cette thèse a pour hypothèse que le CPP du chat est impliqué dans la planification du placement précis du pied lors des modifications volontaires de la marche. Nous avons entraîné les animaux à enjamber des obstacles en mouvement attachés à la ceinture d’un tapis roulant. Afin d’augmenter la nécessité d’intégrer les informations visuelles et proprioceptives, nous avons dissocié la vitesse des obstacles de celle du tapis roulant. Nous avons observé que plus la vision devient critique pour la tâche, plus les déficits sont importants. Notre analyse démontre que ceux-ci résultent d’un placement inapproprié du pied dans le cycle de marche précédant l’enjambement de l’obstacle. Ceci suggère que le CPP est impliqué dans la planification du placement précis du pied pendant la locomotion sous guidage visuel. La vision directe est disponible lors de la modification de l’activité des membres antérieurs, mais n’est plus disponible lorsque l’obstacle passe sous le corps. Par conséquent, la modification de l’activité des membres postérieurs doit être basée sur l’information gardée en mémoire et coordonnée avec celle des membres antérieurs. Notre deuxième étude a pour but de caractériser les mécanismes neuronaux responsables de cette coordination. Nous avons proposé que le CPP soit impliqué dans la coordination des membres antérieurs et postérieurs lors de l’enjambement d’obstacles. Pour tester cette hypothèse, nous avons enregistré l’activité de neurones de l’aire 5 pendant la même tâche. Nous avons découvert deux populations: une qui décharge lors du passage de l’obstacle entre les membres antérieurs et postérieurs et une autre qui décharge lors du passage de l’obstacle par les membres postérieurs. Dans la tâche de dissociation visuelle, la décharge est modifiée en fonction du temps de passage de l’obstacle sous le corps et reflète la modification du couplage entre les membres lors du changement dans la stratégie d’enjambement. De plus, ces mêmes neurones maintiennent une décharge soutenue lorsqu’un obstacle fixe se trouve entre les membres antérieurs et postérieurs ou les deux membres postérieurs (limite testée : 1-2min). Ces neurones pourraient être responsables de l’emmagasinage à plus long terme des caractéristiques d’un obstacle pour le guidage des mouvements des membres postérieurs. Nos résultats suggèrent que le CPP est impliqué dans l’intégration des informations visuelles et proprioceptives pour la planification du placement précis du pied devant un obstacle. Le patron de décharge de nos populations neuronales suggère qu’il encode également l’information temporelle et spatiale concernant la vitesse et la position de l’obstacle afin de coordonner l’activité des quatre membres pendant la tâche. Finalement, nous proposons qu’une des fonctions du CPP soit d’estimer la position des membres par rapport à l’obstacle en mouvement. / During locomotion, vision provides crucial information about the type of terrain one walks on, as well as the size, shape and location of possible obstacles in the path. In the case of a predator, vision also provides information about the speed of a potential prey. The neuronal mechanisms involved in the execution of visually guided gait modifications are now well studied, but those related to their planning remain poorly understood. One likely candidate involved in movement planning is the posterior parietal cortex (PPC). Based on a consideration of the properties of the PPC in visually-guided reaching, the present study was designed to determine the contribution of the PPC to the control of visually-guided locomotion. In the first study presented in this thesis, we hypothesize that the cat PPC is involved in the planning of precise foot placement during voluntary gait modifications. We trained animals to step over moving obstacles attached on a treadmill belt before and after a lesion to area 5. To increase the need for visual and proprioceptive integration, we dissociated the speed of the obstacles from that of the treadmill. We noticed that deficits were largest when the importance of vision was the greatest. Our analysis showed that the deficits were due to inappropriate paw placement prior to the step over the obstacle and thus suggests that the PPC is involved in the planning of precise paw placement during visually-guided locomotion. Direct visual information is available to guide forelimb gait modifications, but is lost when the obstacle passes under the body. Therefore, hindlimb gait modifications must rely on remembered information and must be coordinated with those of the forelimbs. Our second study is designed to determine the neuronal mechanisms responsible for this coordination. We propose that the PPC is responsible for coordinating the activity of the forelimbs and the hindlimbs during obstacle negotiation. To test this hypothesis, we recorded the activity of area 5 neurones in the same task and found two cell populations: one that discharged in relation to the passage of the obstacle between the fore and hindlimbs, and the other between the two hindlimbs. In the visual dissociation task, the discharge was modified to account for the increased time taken by the obstacle to pass under the body and the change in interlimb coupling when cats modified their stepping strategy during the step over the obstacle. We also found that these same cells maintained their discharge when the cat straddled an obstacle either between the fore and hindlimbs or between the two hindlimbs. The discharge was sustained up to the limit tested (~ 1-2min). These neurones could be responsible for the retention of obstacles characteristics to guide future hindlimb movements. Our results provide support for the hypothesis that the PPC is involved in the integration of visual and proprioceptive information for the planning of precise paw placement in front of obstacles. The discharge of our neuronal populations suggests it also encodes temporal and spatial information regarding obstacle’s location and speed to coordinate all four limbs during the task. Finally, we propose that one function of the PPC is to estimate the position of the limbs with respect to the advancing obstacle.

La vision fournit des informations essentielles sur la surface de marche, ainsi que sur la taille, la forme et la position d’obstacles potentiels dans notre environnement. Dans le cas d’un prédateur, la vision fournit également des informations sur la vitesse d’une proie potentielle. Les mécanismes neuronaux impliqués dans l’exécution des modifications de la marche sous guidage visuel sont relativement bien connus, mais ceux impliqués dans la planification de ces modifications de la marche sont peu étudiés. Le cortex pariétal postérieur (CPP) semble être un candidat approprié si l’on considère les propriétés du CPP lors des mouvements d’atteinte vers une cible. Le but des présents travaux est de déterminer la contribution du CPP au contrôle de la locomotion sous guidage visuel. La première étude présentée dans cette thèse a pour hypothèse que le CPP du chat est impliqué dans la planification du placement précis du pied lors des modifications volontaires de la marche. Nous avons entraîné les animaux à enjamber des obstacles en mouvement attachés à la ceinture d’un tapis roulant. Afin d’augmenter la nécessité d’intégrer les informations visuelles et proprioceptives, nous avons dissocié la vitesse des obstacles de celle du tapis roulant. Nous avons observé que plus la vision devient critique pour la tâche, plus les déficits sont importants. Notre analyse démontre que ceux-ci résultent d’un placement inapproprié du pied dans le cycle de marche précédant l’enjambement de l’obstacle. Ceci suggère que le CPP est impliqué dans la planification du placement précis du pied pendant la locomotion sous guidage visuel. La vision directe est disponible lors de la modification de l’activité des membres antérieurs, mais n’est plus disponible lorsque l’obstacle passe sous le corps. Par conséquent, la modification de l’activité des membres postérieurs doit être basée sur l’information gardée en mémoire et coordonnée avec celle des membres antérieurs. Notre deuxième étude a pour but de caractériser les mécanismes neuronaux responsables de cette coordination. Nous avons proposé que le CPP soit impliqué dans la coordination des membres antérieurs et postérieurs lors de l’enjambement d’obstacles. Pour tester cette hypothèse, nous avons enregistré l’activité de neurones de l’aire 5 pendant la même tâche. Nous avons découvert deux populations: une qui décharge lors du passage de l’obstacle entre les membres antérieurs et postérieurs et une autre qui décharge lors du passage de l’obstacle par les membres postérieurs. Dans la tâche de dissociation visuelle, la décharge est modifiée en fonction du temps de passage de l’obstacle sous le corps et reflète la modification du couplage entre les membres lors du changement dans la stratégie d’enjambement. De plus, ces mêmes neurones maintiennent une décharge soutenue lorsqu’un obstacle fixe se trouve entre les membres antérieurs et postérieurs ou les deux membres postérieurs (limite testée : 1-2min). Ces neurones pourraient être responsables de l’emmagasinage à plus long terme des caractéristiques d’un obstacle pour le guidage des mouvements des membres postérieurs. Nos résultats suggèrent que le CPP est impliqué dans l’intégration des informations visuelles et proprioceptives pour la planification du placement précis du pied devant un obstacle. Le patron de décharge de nos populations neuronales suggère qu’il encode également l’information temporelle et spatiale concernant la vitesse et la position de l’obstacle afin de coordonner l’activité des quatre membres pendant la tâche. Finalement, nous proposons qu’une des fonctions du CPP soit d’estimer la position des membres par rapport à l’obstacle en mouvement. / During locomotion, vision provides crucial information about the type of terrain one walks on, as well as the size, shape and location of possible obstacles in the path. In the case of a predator, vision also provides information about the speed of a potential prey. The neuronal mechanisms involved in the execution of visually guided gait modifications are now well studied, but those related to their planning remain poorly understood. One likely candidate involved in movement planning is the posterior parietal cortex (PPC). Based on a consideration of the properties of the PPC in visually-guided reaching, the present study was designed to determine the contribution of the PPC to the control of visually-guided locomotion. In the first study presented in this thesis, we hypothesize that the cat PPC is involved in the planning of precise foot placement during voluntary gait modifications. We trained animals to step over moving obstacles attached on a treadmill belt before and after a lesion to area 5. To increase the need for visual and proprioceptive integration, we dissociated the speed of the obstacles from that of the treadmill. We noticed that deficits were largest when the importance of vision was the greatest. Our analysis showed that the deficits were due to inappropriate paw placement prior to the step over the obstacle and thus suggests that the PPC is involved in the planning of precise paw placement during visually-guided locomotion. Direct visual information is available to guide forelimb gait modifications, but is lost when the obstacle passes under the body. Therefore, hindlimb gait modifications must rely on remembered information and must be coordinated with those of the forelimbs. Our second study is designed to determine the neuronal mechanisms responsible for this coordination. We propose that the PPC is responsible for coordinating the activity of the forelimbs and the hindlimbs during obstacle negotiation. To test this hypothesis, we recorded the activity of area 5 neurones in the same task and found two cell populations: one that discharged in relation to the passage of the obstacle between the fore and hindlimbs, and the other between the two hindlimbs. In the visual dissociation task, the discharge was modified to account for the increased time taken by the obstacle to pass under the body and the change in interlimb coupling when cats modified their stepping strategy during the step over the obstacle. We also found that these same cells maintained their discharge when the cat straddled an obstacle either between the fore and hindlimbs or between the two hindlimbs. The discharge was sustained up to the limit tested (~ 1-2min). These neurones could be responsible for the retention of obstacles characteristics to guide future hindlimb movements. Our results provide support for the hypothesis that the PPC is involved in the integration of visual and proprioceptive information for the planning of precise paw placement in front of obstacles. The discharge of our neuronal populations suggests it also encodes temporal and spatial information regarding obstacle’s location and speed to coordinate all four limbs during the task. Finally, we propose that one function of the PPC is to estimate the position of the limbs with respect to the advancing obstacle.

L’adaptation motrice renvoie à la capacité de notre système nerveux à produire continuellement des mouvements précis et ce malgré le fait que notre environnement ainsi que notre corps puissent être soumis à des modifications. Le transfert d’adaptation entre les membres découle de notre habilité à généraliser ce que l’on a appris, par exemple, avec un bras au bras opposé. Le transfert entre les membres est un objet d’étude complexe. Les conditions amenant au transfert sont largement débattues dans la littérature car les résultats d’une étude à l’autre peuvent être contradictoires. Ce travail de thèse s’inscrit dans une tentative d’apporter une explication concernant l’hétérogénéité des performances et les divergences observées dans les différentes études portant sur le transfert entre les membres. Les deux premières expériences avaient pour but d’identifier si des conditions paradigmatiques ou idiosyncratiques pouvaient influencer les performances du transfert au bras opposé. L’objectif de la troisième expérience était d’étudier l’influence des processus sous-jacents à l’adaptation sur le transfert entre les membres d’après le modèle de Smith et collaborateurs (2006). Nos résultats nous ont permis d’éclaircir certains aspects du transfert concernant les facteurs prédictifs et les processus mis en jeu. Nos deux premières études suggèrent que les différences individuelles sont une source d’information pertinente pour expliquer certains comportements tels que le transfert entre les membres. Notre troisième étude nous a permis de caractériser les processus qui, durant l’adaptation, prédisposent au transfert. / Motor adaptation refers to the capacity of our nervous system to produce accurate movements while the properties of our body and our environment continuously change. Interlimb transfer is a process that directly stems from motor adaptation. It occurs when knowledge gained through training with one arm change the performance of the opposite arm movements. Interlimb transfer of adaptation is an intricate process. Numerous studies have investigated the patterns of transfer and conflicted results have been found. The attempt of my PhD project was to identify which factors and processes favor interlimb transfer of adaptation and thence may explain the discrepancies found in the literature. The first two experiments aimed at investigated whether paradigmatic or idiosyncratic features would influence the performance in interlimb transfer. The third experiment provided some insights on the processes allowing interlimb transfer by using the dual-rate model of adaptation put forth by Smith et al. (2006). Our results show that inter-individual differences may be a key factor to consider when studying interlimb transfer of adaptation. Also, the study of the different sub-processes of adaptation seems helpful to understand how interlimb transfer works and how it can be related to other behaviors such as the expression of motor memory.