Abstracts

Rationale: This study evaluates the frequency of seizures induced by electrical stimulation of the cortical and intracerebral regions, and determines the sensitivity and specificity of the induced secondary generalized seizures (SGSs), complex partial seizures (CPSs), and simple partial seizures (SPSs). Methods: In a consecutive 62 patients with implantation of subdural and intracerebral electrodes, we performed functional mapping studies of 52 patients and evaluated the data of 2074 and 2734 contact points in the left and right cerebral hemispheres, respectively. We conducted 7546 unifocal or bifocal stimulations trials for 275 days. The stimulation parameters were as follows: pulse duration, 0.2 ms; stimulus frequency, 50 Hz of alternative electric current; and stimulus train duration, 2-5 s. In all cases, we began mapping with 1 mA and increased the current until functional changes or afterdischarges occurred, or we increased the current till it attained the maximum intensity of 10 mA. Results: The frequency of spontaneous seizures in 40 patients was 4 times that of induced seizures, i.e., in a total of 1129 seizures, we observed 86 SGSs, 377 CPSs, and 666 SPSs in 23, 33, and 25 patients, respectively. The electrical stimulation elicited 277 seizures in 40 patients; this frequency was 3.7% of all the stimulation trials. SGS was elicited in 28 seizures (0.37%) of 14 patients, CPS in 47 seizures (0.62%) of 16 patients, and SPS in 202 seizures (2.7%) of 30 patients. The positions of 185 and 92 electrodes that induced seizures were within and beyond the resected region, respectively. Assuming that the postsurgical outcome is good after resection of all the seizure-inducing electrodes, the sensitivity and specificity of the induced SGSs, CPSs, and SPSs were 92% and 13%, 59% and 90%, and 69% and 56%, respectively. The frequency of the induced seizures not correlated to the seizure-related zone was 14%, 74% of which was observed around the pre- and post-central gyri. Conclusions: The induced generalized seizure showed a low frequency (0.37%) during the brain stimulation study. The clinical importance of the stimulation-induced seizure is that the specificity of CPS induction is higher than that of SPS and SGS. Although the seizure-induced region is not always included in the seizure-onset zone, the electrical stimulation study plays a partial role in the detection of excitability in the epileptogenic zones and facilitates the identification of the seizure-propagation pathways.