Slow potential changes in experimental neocortical propagated foci.
During and following interhemispheric stimulation (HS), characteristic negative slow potential changes (NSPCs) appeared which coincided with defined patterns of epileptic phasic field potentials (PFPs). Stimulus time-locked, high-amplitude, interhemispheric responses (IHRs), interictal and ictal patterns were accompanied by typical moderate NSPCs. In the wake of the latter, giant NSPCs occurred, concurrent with Van Harrevelds convulsions and/or either total or partial spreading, or local depressions. Partial depression of the PFPs and spreading of the moderate NSPCs were also present in the IHR stage. It is suggested that the moderate and giant NSPCs characterize two distinct types of experimental epileptogenesis which differ in the extent of alteration of the extracellular ion activities.