COUPLING THE NEURAL AND PHYSICAL DYNAMICS IN RHYTHMIC MOVEMENTS

A pair of coupled oscillators simulating a central pattern generator ( CPG) interacting with a pendular limb were numerically integrated. The CPG was represented as a van der Pol oscillator and the pendular limb was modeled as a linearized, hybrid spring-pendulum system. The CPG o scillator drove the pendular limb while the pendular limb modulated th e frequency of the CPG. Three results were observed. First, sensory fe edback influenced the oscillation frequency of the coupled system. The oscillation frequency was lower in the absence of sensory feedback. M oreover, if the muscle gain was decreased, thereby decreasing the osci llation amplitude of the pendular limb and indirectly lowering the eff ect of sensory feedback, the oscillation frequency decreased monotonic ally. This is consistent with experimental data (Williamson and Robert s 1986). Second, the CPG output usually led the angular displacement o f the pendular limb by a phase of 90 degrees regardless of the length of the limb. Third, the frequency of the coupled system tuned itself t o the resonant frequency of the pendular limb. Also, the frequency of the coupled system was highly resistant to changes in the endogenous f requency of the CPG. The results of these simulations support the view that motor behavior emerges from the interaction of the neural dynami cs of the nervous system and the physical dynamics of the periphery.