Model of a pattern generator for locomotion in mammals.

This paper presents an analytic model of a limb pattern generator that can produce complex muscle activation patterns such as those shown to control the limbs of cats. The limb pattern generator is considered to have a tonic input and six outputs; this provides for flexion and extension of representative muscles for each of the three joints of the limb. The pattern generator functions as a community of labile synthesized relaxation oscillators that alters its output in response to input. This model was studied using electromyographic data from an experiment conducted on an acute postmammillary cat preparation. The results suggest that the limb pattern generator can be represented as three subsystems: an oscillator that produces the fundamental frequency of the output in response to the tonic signal, nonlinear shaping functions that mold the oscillator output into the basic complex pattern, and appropriate weighting functions that generate the muscle activity pattern from basic waveforms. The model can account for speed changes in locomotion with a relatively smooth change of system parameters. The pattern generator model is generative, amenable to simulation studies, and can be realized by a neural network.