More intense focal seizure types after callosal section: the role of inhibition.

Corpus callosum section reduces the incidence of generalized seizures associated with loss of consciousness. Minimal data are available, however, regarding the types of seizures that may be present following surgery. Five of 17 patients in our clinic who underwent partial or complete corpus callosum section developed more intense and sometimes newly patterned (but not necessarily more frequent) focal seizures postoperatively. These patients were not predictably different from the other 12 in terms of age at onset of seizures or at surgery, cause of seizures, extent of callosum sectioned, radiographically demonstrable structural lesions, or the types of preoperative seizures. All 5 patients, however, had bilateral independent frontal electroencephalographic foci. No patients without these electroencephalographic findings developed more intense focal seizures after surgery. The findings are consistent with the results of experimental animal studies and argue for a suppressive influence of the contralateral hemisphere on some types of seizures.