Meeting Abstract
23.2 Jan. 5 Integration of the pattern generation and multiple feedback pathways for the control of locomotion. A neuromusculoskeletal model. YAKOVENKO, Sergiy*; PROCHAZKA, Arthur; Universit� de Montr�al; University of Alberta sergiy.yakovenko@umontreal.ca
Though not essential for the generation of locomotor activity, multiple sensory pathways participate in the locomotor control. In this study we investigated how stretch reflexes and multisensory If-Then rules interact with the output from the pattern generator and the intrinsic stabilizing properties of muscles during gait on level and variable terrain. We constructed a two-legged planar model with 9 segments, driven by 12 musculotendon actuators with Hill-type force-velocity and monotonic force-length properties. The locomotor pattern generator provided a stereotyped rhythmical pattern of activity to drive the simulated muscle groups with the patterns based on EMG profiles of the corresponding muscles during slow level locomotion. Muscle spindle Ia and tendon organ Ib afferent inputs were represented by transfer functions with a reflex latency of 35 ms, contributing a preset amount of the net EMG profile and gated to be active only when the receptor-bearing muscles were contracting. If-Then rules triggered swing-stance and stance-swing transitions in the activity of the pattern generator when multisensory conditions, based on muscle length and force, were met. We found that a wide range of combinations of the relative muscle strengths in a model with and without stretch reflexes may result in stable locomotion. The model demonstrated that the decrease in the pattern generator drive can be �rescued� by the stretch reflex pathway, potentiated by interactions with intrinsic muscle properties. Furthermore, we found that the gain of stretch reflexes is inversely related to the amount of the central drive from the pattern generator during locomotion. Finally, multisensory If-Then rules provided a robust mechanism for the regulation of phase duration for stable locomotion at a wide range of model velocities.
