Cortical stimulation and epileptic seizure: a study of the potential risk in primates

The recent successful development of chronic stimulation of the motor cortex as a treatment for neuropathic and central pain does not exclude the possibility of eventual side effects, such as epileptic seizure or a lowering of the epileptic threshold. This study evaluates the behavioral and electroencephalographic impact of this treatment in three normal monkeys.

None of the monkeys presented epileptic behavior or abnormal electroencephalographic activity at parameters of stimulation currently used in clinical series, i.e., frequency and pulse duration of approximately 40 Hz and 90 microseconds, respectively, and an intensity just under the threshold for inducing muscle twitch in painful areas. Higher intensities did, however, induce reversible epileptic seizure. There was, nonetheless, no modification of the epileptic threshold, because even after these seizures, intermittent light stimulation elicited no abnormal electroencephalographic activity.

It thus seems that motor cortex stimulation does not induce epileptic complications when the classic clinical criteria of stimulation are respected. Nevertheless, it would be wise to subject candidates for implantation to intermittent light stimulation before and after a period of stimulation to ascertain the innocuousness of the cortical stimulation.