The incidence of spreading depression, which was elicited by interhemispheric stimulation, increased with prolonged duration and strength of individual pulses and with longer stimulus trains. In the first trial spreading depression appeared in one-third of the experiments, in two-thirds it was activated by repeated stimulus trains. Both the activated and the first trial spreading depression were preceded by alternation of the interhemispheric response and often by self-sustained afterdischarges. All the phases of the interhemispheric response patterns contained inhibitory components either in the form of phasic focal polarizing waves of the evoked and self-sustained field potentials or giant slow spreading depolarizations. The stimulation parameters determine whether a permanent increase of excitability prevails, as in Goddard's kindling procedures, or whether inhibitory patterns, described in this paper, result from the stimulation.

Institute of Physiology Czechoslovak Academy of Sciences Prague Czechoslovakia

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Epilepsy Research in the Institute of Physiology of the Czech Academy of Sciences in Prague