42.4 Thursday, Jan. 5 A hybrid neuromechanical system for studying reflex reversal in crayfish CHUNG, BP*; LINAN-VELEZ, G; CATTAERT, D; EDWARDS, DH; Georgia State University; Georgia State University; University of Bordeaux 1; Georgia State University firstname.lastname@example.org
Resistance reflexes help to stabilize posture against outside perturbation. During voluntary movement, however, these types of reflexes can lead to interference. In both vertebrates and some invertebrates, descending motor commands include excitation of inhibitory interneurons that prevent unwanted reafference through primary afferent depolarization (PAD). In crayfish, the coxo-basal chordotonal organ (CBCO) is a stretch receptor that spans the coxa-basipodite joint that enables the walking legs to move up and down. CBCO afferents mediate resistance reflexes to maintain leg position during standing, but during walking those resistance reflexes are reversed to produce assistance reflexes. To study how reflex reversal occurs in a closed-loop system, we record from CBCO afferents, central neurons (CNS), and depressor (Dep) and levator (Lev) motorneurons (MNs). The isolated nervous system is connected to a computational neuromechanical model of the crayfish thorax and leg forming a real-time, closed-loop hybrid system. Dep and Lev MN activity excite model Dep and Lev muscles that move the model leg. The leg movement stretches and releases the model CBCO. Changes in the model CBCO length are transduced into identical movements of the live CBCO which generates afferent responses that excite the CNS. We use this system to determine the dynamic changes in reflex loop gains as the system switches from resistance to assistance reflexes during the onset of locomotor central pattern generator (CPG) activity.