Cross-modal sensory signaling shapes vestibulo-motor circuit specificity

The ability to continuously adjust posture and balance is necessary for reliable motor behavior.
Vestibular and proprioceptive systems influence postural adjustments during movement by signaling functionally
complementary sensory information.
Using viral tracing and mouse genetics, we reveal two patterns of synaptic specificity between brainstem
vestibular neurons and spinal motor neurons, established through distinct mechanisms. First, vestibular input
targets preferentially extensor over flexor motor pools, a pattern established by developmental refinement
in part controlled by vestibular signaling. Second,
vestibular input targets slow-twitch over fast motor neuron subtypes within extensor
pools, while proprioceptors exhibit inversely correlated connectivity profiles. Genetic
manipulations affecting the functionality of proprioceptive feedback circuits lead to
adjustments in vestibular input to motor neuron subtypes counterbalancing the
imposed changes, without changing the sparse vestibular input to flexor pools. Thus,
two sensory signaling systems interact to establish complementary synaptic input
patterns to the final site of motor output processing.