SUBTHRESHOLD DYNAMICS IN PERIODICALLY STIMULATED SQUID GIANT-AXONS

Action potentials resulting from periodic stimulation of nerve axons o ccur at intervals that are irregular at moderate stimulation frequenci es. Histograms of the intervals are multimodal, as seen in stochastic resonance. At higher stimulation frequencies, the action potentials ar e suppressed entirely, leaving only subthreshold dynamics. Return maps constructed from data show that both types of response are governed b y the same deterministic one-dimensional description, with an unstable subthreshold fixed point largely accounting for the irregular interva ls at moderate stimulation frequencies.