Department of Biology
University of Toronto Mississauga
Sensory cortices modulate innate motor behaviours throughout corticofugal projections that target phylogenetically-old brainstem nuclei. However, it remains unknown whether the functional properties of these projections match the properties of the innate behaviours they modulate. Here, I will present evidence that visual cortical neurons projecting to the brainstem optic-tract and dorsal-terminal nuclei (NOT-DTN) transmit motion signals relevant to the optokinetic reflex (OKR), a brainstem-mediated innate eye movement that is paramount for vision. Remarkably, enriched in specific visual areas these neurons prefer temporo-nasal visual motion, sharing the direction bias of downstream NOT-DTN neurons. Furthermore, the activity of temporo-nasally biasing cortical neurons is selectively enhanced when OKR is potentiated. These functional specificities allow efficiently integrating cortical input in NOT-DTN neurons to support OKR potentiation. Lastly, I will pinpoint the synaptic target of the corticofugal projection by showing that the visual cortex innervates only one subpopulation of NOT-DTN neurons, which project specifically to the inferior olive (IO) in the brainstem. This IO projecting NOT-DTN population also prefers the temporo-nasal motion, and is critical for the cortical contribution to the OKR. Overall, our results provide compelling evidence that a direction-selective descending pathway connects the visual cortex and brainstem, which conducts functionally relevant information and specializes in adaptively modulating the OKR.