Design of mechanosensory feedback during undulatory locomotion to enhance speed and stability.

Undulatory locomotion relies on the propagation of a wave of excitation in the spinal cord leading to consequential activation of segmental skeletal muscles along the body. Although this process relies on self-generated oscillations of motor circuits in the spinal cord, mechanosensory feedback is crucial to entrain the underlying oscillatory activity and thereby, to enhance movement power and speed. This effect is achieved through directional projections of mechanosensory neurons either sensing stretching or compression of the trunk along the rostrocaudal axis. Different mechanosensory feedback pathways act in concert to shorten and fasten the excitatory wave propagating along the body. While inhibitory mechanosensory cells feedback inhibition on excitatory premotor interneurons and motor neurons, excitatory mechanosensory cells feedforward excitation to premotor excitatory interneurons. Together, diverse mechanosensory cells coordinate the activity of skeletal muscles controlling the head and tail to optimize speed and stabilize balance during fast locomotion.