CORTICAL CIRCUITRY FOR TOP-DOWN SELECTION OF VISUAL INPUTS

Washington University, Saint Louis MO

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Abstract

DESCRIPTION (provided by applicant): The matrix of cerebral cortex consists of iterated circuits whose local, intra-areal connections account for 90% of excitatory synapses. When activated, these circuits generate positive feedback that is kept in check by local inhibition and plays a role in the selection of inputs and the restoration of signals from the outside world. Within mouse primary visual cortex (V1), non-overlapping groups of pyramidal cells with distinct projections to the higher visual areas LM and AL are connected within each population through horizontal networks. These networks provide influences from topographically distant points and are responsible for contour integration and image segmentation. This form of contextual processing is influenced by attention, expectation and perceptual task, suggesting that feedback from the ventral stream area, LM, and the dorsal stream area, AL, preferentially interacts with LM- and AL-projecting horizontal networks within V1. The top-down influences from LM and AL may be functionally specialized for object categories and temporal context, respectively, and disruption of interactions with specific horizontal V1 networks may lead to behavioral disorders. Direct evidence for interactions between context-processing local networks and top-down pathways, however, is lacking. Here, we propose to study whether: (1) LM- and AL-projecting neurons form separate V1 subnetworks, (2) feedback from the dorsal stream area, AL, and the ventral stream area, LM, preferentially interacts with the subnetwork from which it receives feedforward input, and (3) the LM-projecting ventral stream subnetwork is less strongly inhibited by feedback input from LM, than by feedback from the functionally different dorsal stream area, AL. We propose to study these questions by performing whole-cell patch clamp recordings form pairs of identified pyramidal neurons and interneurons in acute slices of mouse visual cortex, and to use subcellular channelrhodopsin-assisted circuit mapping to characterize the specificity of feedback inputs from dorsal and ventral streams to different excitatory and inhibitory V1 subnetworks.