Control of burst proportion and frequency range by drive-dependent modulation of adaptation

Factors controlling burst proportion in oscillatory networks are analyzed. This question is motivated by the lamprey swimming motor pattern which, independently on burst frequency, is characterized by a constant burst proportion. We investigate the effect of active modulation of the relative influence of a slower and faster adaptation controlling the depolarized phase. Using Morris–Lecar oscillators, NMDA-dependent oscillations or a network of mutually excitatory neurons, it is shown that the burst proportion can be controlled by increasing what corresponds to adaptation. Oscillations occur over an extended range of background stimulation values, leading to a higher maximal frequency.