Brain-wide connectivity map of mouse thermosensory cortices

ABSTRACT In the thermal system, skin cooling is represented in the primary somatosensory cortex (S1) and the posterior insular cortex (pIC). Whether S1 and pIC are nodes in anatomically separated or overlapping thermal sensorimotor pathways is unclear, as the brain-wide connectivity of the thermal system has not been mapped. We address this using functionally targeted, dual injections of anterograde viruses or retrograde tracers into S1 and pIC. Our data show that inputs to S1 and pIC originate from two non-overlapping populations, supporting the existence of parallel input pathways. While outputs from S1 and pIC were more widespread and share a number of cortical and subcortical regions, within target structures axonal projections were often separable. We observed a high degree of reciprocal connectivity with thalamic and cortical regions from both S1 and pIC, but output to the mid- and hind-brain was unidirectional. Notably, pIC showed exclusive connectivity with regions associated with thermal processing. Together, these data indicate that cutaneous thermal information is routed to the cortex via multiple, parallel streams of information which are forwarded to overlapping downstream regions for the binding of complex somatosensory percepts and integration with ongoing behavior.