Multisensory and motor integration in the non-human primate: anatomical, behavioral and electrophysiological approaches
Intégration multisensorielle et motrice chez le primate non humain : approches anatomique, comportementale et électrophysiologique
Résumé
In order to interact with the multimodal world which surrounds us, we must integrate simultaneously
various sources of sensory information (vision, hearing, body sensation...). A fundamental question is thus
to know how the brain integrates the separate elements of an object defined by several sensory components
to form a unified percept. The superior colliculus was the main model to study the polymodal integration.
At the cortical level, until recently, polymodal integration appeared to be a characteristic that only had the
associative areas located at the top of the information processing hierarchy. First of all, our first study
related to cortico-cortical connections and showed the existence of direct projections between cortical areas
of different sensorialities in the non human primate. Then, the study of projections between different
sensory and motor cortical areas and the thalamus enabled us to highlight the existence of thalamic nuclei
which, by their connections, could represent an alternative pathway for the information transfer of different
sensory and/or motor cortical areas. The thalamus could allow a faster transfer and even an integration of
information. In addition, at the behavioral level, multisensory integration allows an improvement of
perception. An experiment conducted in macaques monkeys in a detection task of unimodal and bimodal
stimuli showed the presence of a significant multisensory gain which is highest at threshold level, which
decreases for increasing intensities above threshold and which disappears at high intensities. Lastly, in
these animals showing this multisensory gain on the behavorial side, we explored the mechanisms
underlying multisensory integration at the neuronal level in the auditory cortex. Thus, using anatomical,
behavioral and electrophysiological approaches, our results provide fundamental elements on the cerebral
structures implied in multisensory integration, their connections and the mechanisms existing in the brain to
treat in an effective way different sensory information, in order to initiate a motor response.
various sources of sensory information (vision, hearing, body sensation...). A fundamental question is thus
to know how the brain integrates the separate elements of an object defined by several sensory components
to form a unified percept. The superior colliculus was the main model to study the polymodal integration.
At the cortical level, until recently, polymodal integration appeared to be a characteristic that only had the
associative areas located at the top of the information processing hierarchy. First of all, our first study
related to cortico-cortical connections and showed the existence of direct projections between cortical areas
of different sensorialities in the non human primate. Then, the study of projections between different
sensory and motor cortical areas and the thalamus enabled us to highlight the existence of thalamic nuclei
which, by their connections, could represent an alternative pathway for the information transfer of different
sensory and/or motor cortical areas. The thalamus could allow a faster transfer and even an integration of
information. In addition, at the behavioral level, multisensory integration allows an improvement of
perception. An experiment conducted in macaques monkeys in a detection task of unimodal and bimodal
stimuli showed the presence of a significant multisensory gain which is highest at threshold level, which
decreases for increasing intensities above threshold and which disappears at high intensities. Lastly, in
these animals showing this multisensory gain on the behavorial side, we explored the mechanisms
underlying multisensory integration at the neuronal level in the auditory cortex. Thus, using anatomical,
behavioral and electrophysiological approaches, our results provide fundamental elements on the cerebral
structures implied in multisensory integration, their connections and the mechanisms existing in the brain to
treat in an effective way different sensory information, in order to initiate a motor response.
Afin d'interagir avec le monde multimodal qui nous entoure, nous devons intégrer simultanément différentes sources d'informations sensorielles (vision, audition, somesthésie...). Une question fondamentale est donc de savoir comment le cerveau intègre les éléments séparés d'un objet défini par plusieurs composantes sensorielles pour former un percept unifié. Le colliculus supérieur a été le principal modèle d'étude de l'intégration polymodale. Au niveau cortical, jusqu'à récemment, les phénomènes d'intégration polymodale paraissaient être une caractéristique que seules possédaient les aires associatives situées au sommet de la hiérarchie du traitement de l'information. Tout d'abord, notre première étude a porté sur les connexions cortico-corticales et a montré l'existence de projections directes entre aires corticales de sensorialités différentes chez le primate non humain. Ensuite, l'étude des projections entre différentes aires corticales sensorielles et motrices et le thalamus nous a permis de mettre en évidence l'existence de noyaux thalamiques qui, par leurs connexions, pourraient représenter une voie alternative pour le transfert des informations de différentes aires corticales sensorielles et/ou motrices. Le thalamus pourrait permettre un transfert plus rapide et même une intégration des informations. Par ailleurs, au niveau comportemental, l'intégration multisensorielle permet une amélioration de la perception. Une expérience que nous avons menée chez des singes macaques dans une tâche de détection de stimuli unimodaux et bimodaux a montré la présence d'un gain multisensoriel significatif qui est le plus marqué près du seuil, qui diminue pour des intensités croissantes au-dessus du seuil et qui, enfin, disparaît à fortes intensités. Enfin, chez ces animaux montrant sur le plan comportemental ce gain multisensoriel, nous avons exploré les mécanismes sous jacents de l'intégration multisensorielle au niveau des neurones du cortex auditif. Nous avons trouvé des neurones dont les propriétés de décharges reflètent une synergie multisensorielle entre audition et vision. Ainsi, par des approches anatomiques, comportementales et électrophysiologiques, nos résultats apportent des éléments fondamentaux sur les structures cérébrales impliquées dans l'intégration multisensorielle, leurs connexions et les mécanismes existant dans le cerveau pour traiter de façon efficace les différentes informations sensorielles, en vue de la genèse d'une réponse motrice.