ANATOMY AND PHYSIOLOGY OF CORTICOTHALAMIC PATHWAYS

All neocortical areas receive projections from and project back to the thalamus. It is generally admitted that the corticothalamic (CT) projections are organized in a way that reciprocates the spatial distribution of thalamic pathways.

Our current work examines to what extent this principle of reciprocity is supported by the projection patterns of the CT cells of the vibrissal sensory cortex in the rat. Current evidence indicates the existence of both, reciprocal and non reciprocal patterns of CT connectivity. These observations have led us to propose that the spatial organization of the CT connections complies with a more fundamental rule, termed rule of parity, from which reciprocity follows as a general, but not obligatory, consequence. The rule of parity states that the patterns of CT projections from a cortical region are determined by the connectivity patterns of the different classes of prethalamic afferents that influence that region via the thalamus. The anatomical, developmental and physiological implications of this rule are investigated by means of anterograde labeling of single axons and extra- and intracellular recordings in vivo.

These projects are supported by the Medical Research Council of Canada.

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