Ictal-interictal unit firing pattern differences in penicillin-induced primary and secondary epileptogenic foci

Single-unit activity occurring during seizures and interictal periods was studied in primary (penicillin) and secondary (mirror) neocortical epileptogenic foci in the rat. The results revealed that significant differences exist between the behavior of primary and dependent secondary focus neurons. The most prominent difference appeared to be the marked tendency for suppression of neuronal firing in secondary focus units, which was evident both interictally and during seizures. Moreover, seizures did not appear to be more potent than interictal discharges alone, in shifting the firing patterns of secondary focus neurons toward that displayed by primary focus neurons. These data have relevance for current theories regarding the induction of independent (chronic) secondary epileptogenic foci.