Where top-down meets bottom-up: Cell-type specific connectivity map of the whisker system

Abstract

AbstractSensorimotor computation is a closed-loop process where bottomup information collected about the current state of the world is integrated with top-down, internally generated knowledge and task- and goal-related affordances to create an action plan. In the rodent whisker system, a canonical model of sensorimotor computation in the context of active sensing, emerging evidence suggests that neuromodulatory neurotransmitters help shape sensorimotor control of the whisker position and contribute to context-dependent changes in whisking frequency and amplitude. Since neuromodulatory neurotransmitters are mostly released from subcortical nuclei and have long-range projections that reach the rest of the central nervous system, mapping the circuits of top-down neuromodulatory control of sensorimotor nuclei will help to systematically address the mechanisms of active sensing. Therefore, taking advantage of the Allen Institute’s Mouse Connectivity database, we provide an updated, cell-type specific map of the sensorimotor circuits in the mouse brain. The map includes 138 projections (54 of which were not previously reported in the literature) across 18 principal and neuromodulatory neurotransmitterreleasing nuclei of the whisker system. Performing a graph network analysis of this connectome, we identify cell-type specific hubs, sources, and sinks, provide anatomical evidence for monosynaptic inhibitory projections into all stages of the ascending pathway, and show that neuromodulatory projections improve network-wide connectivity. These results argue that beyond the modulatory chemical contributions to information processing and transfer in the whisker system, the circuit connectivity features of the neuromodulatory networks position them as nodes of sensory and motor integration.