PATTERN GENERATION BY 2 COUPLED TIME-DISCRETE NEURAL NETWORKS WITH SYNAPTIC DEPRESSION

Numerous animal behaviors, such as locomotion in vertebrates, are prod uced by rhythmic contractions that alternate between two muscle groups . The neuronal networks generating such alternate rhythmic activity ar e generally thought to rely on pacemaker cells or well-designed circui ts consisting of inhibitory and excitatory neurons. However, experimen ts in organotypic cultures of embryonic rat spinal cord have shown tha t neuronal networks with purely excitatory and random connections may oscillate due to their synaptic depression, even without pacemaker cel ls. In this theoretical study, we investigate what happens if two such networks are symmetrically coupled by a small number of excitatory co nnections. We discuss a time-discrete mean-field model describing the average activity and the average synaptic depression of the two networ ks. Depending on the parameter values of the depression, the oscillati ons will be in phase, antiphase, quasiperiodic, or phase trapped. We p ut forward the hypothesis that pattern generators may rely on activity -dependent tuning of synaptic depression.