Model for simulating cyclic variations in focal epileptogenic excitability

During 0.2 to 1.0 Hz stimulation of an epileptogenic focus, the phenomenon of cyclic spike driving (CSD) occurs, wherein 20- to 40-sec active periods, in which each stimulus triggers an all-or-none interictal event (IE), alternate with quiet periods of similar duration, in which IE are not triggered. CSD was simulated by a model in which individual IE are followed by biphasic response functions which sum linearly to produce long-term oscillations of epileptogenic excitability relative to the IE triggering threshold. The model successfully simulates all of the major characteristics of experimentally induced CSD, including the effects of manipulating stimulus parameters. Results of the simulation provide clues as to the time course of mechanisms which control epileptogenic triggerability.