Mécanismes de la plasticité neuronale et de l'encodage des signaux visuels

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Our research program is centered on two important topics in neuroscience: A) mechanisms of neuronal plasticity, and B) encoding processes of sensory signals. The ability of adult sensory nerve cells to adapt their response to changing stimuli is an important capability of neurons. We propose a series of experiments aimed at studying the physiological mechanisms responsible for cortical plasticity following adaptation in the visual cortex of anesthetized adult cats. The following properties will be investigated: orientation and spatial frequency preferences, direction velocity selectivities. More specifically, we will study the role of inhibition in attractive and repulsive shifts of the peak of the tuning curves. Several drugs linked to glutamate receptors are believed to facilitate or prevent cortical plasticity. We will test the effect of local drug application on the ability of neurons to change their preferred stimulus after adaptation. Using intrinsic optical imaging we will study the modifications of composite orientation maps. Specifically, pinwheels, and cardinal and oblique orientation domains will be compared to provide a detailed structural map after adaptation. We will examine how cells in area 18 react to plasticity in area 17 cells. That is, we will analyze the influence of adaptation inherited from earlier cortical areas. In parallel, we will investigate the relationships between image structures and response patterns and synchronization indexes, in a pairwise fashion, testing the hypothesis that firing patterns and synchronization are related to signal processing. A dissimilarity index (1-r, Pearson coefficient) will correlate evoked firing patterns and stimuli applied within a cell's receptive field(s). A second correlation will compare synchronization indexes induced by two trains of action potentials in response to the same image properties. The above computations will permit establishing two distinct representational dissimilarity matrices for both areas (17 and 18). These computations will allow us to determine which property dominates and hence guide the establishment of category-sensitive subregions in areas 17 and 18. We may then determine if firing rates or synchronization are more sensitive, and thus more reliable, in coding image properties.