Brainstem circuits involved in skilled motor performance

MARIA SOLEDAD ESPOSITO; PAOLO CAPELLI; SILVIA ARBER

Basilea

Congreso; Biozentrum Synposium; 2013

Descending commands from the brain to the spinal cord are essential for the generation of skilled movements. Although many descending pathways have been described, their particular role in precise movement control remains elusive. Highly crucial in motor control is the direct input to motor neurons that can by-pass the stereotypic commands generated by spinal circuits. To begin to pinpoint the possible brain regions involved in skilled motor performance, we used monosynaptically restricted trans-synaptic rabies viruses to visualize premotor neurons in the brain connecting to forelimb or hindlimb motor neurons in the spinal cord. Within a reconstructed three-dimensional premotor brainstem model, we observe striking differences in the access of descending input to distinct spinal motor neurons. We highlight a subpopulation of neurons in the medullary reticular formation ventral part (MdV) as a key brainstem area specifically connecting to a subset of forelimb innervating spinal motor neurons. We show that excitatory MdV neurons receive input from upstream motor control centers, are active during motor behavior, and essential for performance of a skilled motor task. Our findings provide a circuit- and subpopulation level connectivity map for descending pathways regulating limb motor control and put forward a model, in which distinct brainstem hubs differentially address spinal motor neurons to control motor actions.