Monosynaptic trans-collicular pathways link mouse whisker circuits to integrate somatosensory and motor cortical signals

Abstract

Most brain circuits comprise intermingled neuronal populations with heterogeneous input and output connectivity, which limits the ability to unambiguously map how the circuit of interest synaptically links specific input pathways to specific downstream targets. By applying newly available transsynaptic and intersectional tracing tools to investigate input-output connectivity of the superior colliculus (SC), a conserved midbrain-node with extensive long-range connectivity throughout the brain, we identify hitherto unknown connectivity features underlying cortical control of SC sensory-motor transformations. We pinpoint a whisker region in the SC of mice as a node for the integration of somatosensory and motor cortical signals. Tracing input-defined pathways from brainstem, motor- and somatosensory cortices to the whisker SC and further on to collicular downstream targets in the midbrain and brainstem revealed that long-range inputs establish synaptic contacts with inhibitory and excitatory SC-output neurons, thereby providing monosynaptic trans-collicular pathways between specific cortical and subcortical circuits for somato-motor integration.