Abstracts

Deep brain stimulation has been used to prevent seizures in humans. One Hz stimulation in animals is known to induce long-lasting synaptic depression and may inhibit seizures. We studied the effect of 1 Hz intracranial stimulation in the epileptogenic focus on interictal spiking and intracranial EEG power spectra in humans.
Subjects were patients (n=6) with CPS disorder admitted for intracranial EEG study. Their identified seizure focus (n=3 hippocampus, n=3 neocortex) and a distant non-epileptogenic brain area (n=4 neocortex, n=1 contralateral hippocampus) were stimulated interictally at 1 Hz, 0.2 msec bipolar square wave pulses, at 5-10 mA (stimulus strength which did not induce afterdischarges) for 15 min. Intracranial EEG data was collected for 15 min before and after stimulation and analyzed for spike count and changes in the EEG power spectrum at the epileptogenic focus in response to 1) stimulation at the focus and 2) stimulation at a non-epileptogenic site (control). Data from 15 min prior to the 1 Hz stimulation (baseline) was compared to data obtained for 15 min following the stimulation.
In 5 out of 6 patients the epileptogenic focus had high interictal spiking, while the non-epileptogenic sites had no interictal spike activity. None of the patients experienced clinical seizures during stimulation. Data from one patient who had several subclinical discharges throughout the study and from one patient with no spike activity in the epileptogenic focus was not included in the spike analysis. One Hz stimulation at the seizure focus caused 64% decrease in the spike activity in all 4 patients (p[lt]0.02, paired t-test comparing data averaged over 5 min pre- and post-stimulus). The decrease in the spike activity returned to baseline levels by 7 min post-stimulus. Stimulation at the non-epileptic control site caused no significant change in the epileptogenic focus (p[gt]0.05). Stimulation at the seizure focus caused a decrease in total EEG power (p [lt] 0.05) at the seizure focus for 5 min starting 5 min post-stimulation and an increase in total power at distant sites.
One Hz 15 min stimulation in the human brain results in enduring suppression of spike activity and changes in the EEG power spectrum within the stimulated seizure focus. While the effects on the spike activity are local, the effects on the EEG power spectrum appear to be both widespread and frequency specific. This work suggests that intracranial 1 Hz stimulation of the seizure focus is safe and may have future applications for seizure suppression.
[Supported by: NIH P01-NS-39092 and BIRCRH 1K12DA14038-01 for I. Cavus]