Motor-sensory loops in insect locomotion: adaptive control of centrally-coupled pattern generator circuits

Animals’ ability to demonstrate both stereotyped and adaptive locomotor behavior is largely dependent on the interplay between centrally-generated motor patterns and the sensory inputs that shape them. Theoretical predictions suggest that the degree to which sensory feedback is used for coordinating movement depends on the specific properties of the movement and the environment; i.e when animals navigate slowly through a complex environment where great precision is required, motor activity is expected to be mostly modulated by neural reflexes and sensory information. In contrast, during fast running or under noisy conditions, the relatively slow neural processing makes feedback-based coordination unlikely. The research project I would like to present is our attempt to study the relative importance of central coupling of pattern generating networks vs. intersegmental afferents for locomotion in the cockroach, an animal that is renowned for rapid and stable running. In order to do so, we combine neurophysiological experiments with simulations of stochastic models of coupled oscillators. Specifically, we record activity patterns from leg motor neurons in semi-intact preparations whose legs movement is controlled. The recorded traces are then compared with model generated activity to estimate underlying physiological parameters using a maximum likelihood technique. Our findings suggest segmental hierarchies, speed-dependent control and provide insights into how sensory information from a moving leg dynamically modulates centrally generated patterns. I will discuss these and suggest movement-based feedback in cockroach locomotion as a model system to study the bidirectional interactions between motor control and sensory processing in general.