Lack of interhemispheric transfer of the I-Hz suppression effect in rats

Three experiments were conducted to evaluate the effect of 1-Hzbrain stimulation of the amygdala on kindling behavior induced by 60-Hz sine-wave stimulation in the contralateral amygdala. In Experiment 1, the effective threshold intensity (ETI) to elicit a kindled response with 60-Hz stimulation was determined on four separate occasions with 15 trials between determinations (three per day) for each of three groups. Experimental rats in Group 1 were stimulated with 1-Hz sine waves in one amygdala, then with 60-Hz current in the opposite amygdala, followed by 1-Hz stimulation of the first site (1-60-1, OA), with 1-h interstimulation intervals. Group 2 was treated with the 1-60-1 pattern, but with all stimulation in the same amygdala (1-60-1, SA). Group 3 received only the 60-Hz stimulation trials (X-60-X), on the second trial. Group 2 showed the typical suppression result, a gradual increase in threshold over the four ETI determinations. However, Group l's responses were similar to those of Group 3: ETI values decreased gradually over the determinations. Later, when Group 1 received a set of trials in which 1and 60-Hz current stimulation was to the same site, suppression responses occurred. Two further experiments were conducted with similar results. These results suggest that the suppression effect generated by 1-Hz stimulation appears to involve a local process, an intrahemispheric effect.