Kindling epileptogenesis in orbital and mesial frontal cortical areas of subhuman primates.

Despite ready bilateralization of ictal and interictal EEG discharge throughout cortical kindling, the rate of convulsive seizure development was slow at both orbital and mesial frontal sites, even in the epileptic baboon. However, convulsive generalization occurred swiftly from the mesial frontal cortical (MF) sites once conjugate head, eye, and body adversion developed in the three primate species examined. Only epileptic baboons developed Stage 5 bisymmetrical and bisynchronous convulsion. Stimulation of the contralateral homotopic mesial cortical site readily produced afterdischarge that remained localized and convulsive seizure development did not occur. The findings suggest that (a) the frontal lobe plays an important role in the generation of nonconvulsive seizures, (b) the frontorolandic cortex plays a unique role in convulsive seizure generalization, (c) the role of the intrinsic (genetic) factor is significant in determining the quality of the kindled seizure, and (d) the development of focal epileptogenesis at one MF site interferes with clinical seizure development at the "mirror focus." Our findings underscore (a) the necessity of the conceptual differentiation between the EEG mirror focus and the epileptogenic focus capable of generating clinical seizures and (b) the importance of dissecting interictal behavior reflecting a "continuous disorder of neuronal function," which may cause symptoms other than seizures.