The effect of varying durations of stimulation of the 3-Hz interference effect

Abstract

Experiments were conducted to evaluate the effect of various durations of 3-Hz brain stimulation on kindling behavior induced by 60-Hz sine-wave stimulation of the amygdala. In two experiments the effective threshold intensity (ETI) to elicit a convulsion was determined on four separate occasions with 5 days of daily trials interspersed between determinations. On each day experimental rats were stimulated with 3-Hz current on the first and third trials for 5, 15, 30, 60, 120, or 300 sec duration and with 60-Hz current for 30 sec on the second trial. A steady increase in the intensity required to elicit a convulsion with 60-Hz current from ETI1 to ETI4 resulted for all rats with durations of 15 sec or greater. Rats stimulated only with 60-Hz sine waves and those in the 5-sec group maintained relatively stable values from ETI1 to ETI4, with a slight decline occurring. Suppression of the expected 60-Hz-induced convulsive behavior on daily trials was modest in the 15-sec group, pronounced with the 30-sec group, and drastic with the other groups. The 300-sec group had the greatest suppressive effect operating. The suppression effect appeared not to be due to tissues damage inasmuch as many of the experimental rats (except the 300-sec group) convulsed again at previous low ETI levels following a 16-day rest at the end of the experiment. This result suggests that the suppression effect is a relatively transient event.