Linking cortical circuits to subcortical output structure

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Integrated perception of the outside world emerges from the processing of sensory information in multiple areas of the cerebral cortex. It is generally believed that the multiple cortical areas are reciprocally interconnected by an intricate network of feedforward and feedback connections. Forward connections provide information from lower to higher areas for further (bottom-up) processing. Feedback connections send information from higher areas and modulate lower areas activity (top-down). From these types of connections, a general hierarchical model of cortical processing has been proposed and has been applied to primates, cats and rodents. These types of cortical connections are defined by the distribution of the cells of origin and their terminal axons in the 6 layers of the cerebral cortex. This gross pattern of laminar distribution of axonal terminals is the result of the sum of a host of single axons. Observations of single axons show a variety of termination patterns some of which are common to both forward and backward connections. There is yet no in depth understanding of the microcircuits that constitute these cortical macrocircuits. The main objective of the present proposal is to study the links between cortical connectivity and cortical output structure. We will study the axonal architecture of feedback connections to the primary visual cortex from the extrastriate cortices. We will study the brain wide monosynaptic connectivity on corticofugal projections neurons and the spatial distribution of synaptic contacts of distinct feedback visual pathways on the dendritic arbors of target specific corticofugal neurons of the primary visual cortex. This will provide basic knowledge on the organisation of long-range cortical connections.