Abstracts

The aim of the study is to investigate the effect of a short train of electric pulses at high frequency on the primary motor area (M1), primary somatosensory area (S1), and supplementary motor area (SMA) in epileptic patients undergoing functional cortical mapping for presurgical evaluation., Ten patients (two females and eight males; age range 13 - 36 years) were studied. All underwent chronic long-term video/EEG monitoring and cortical mapping by 50Hz electric cortical stimulation. After these clinical evaluations, cortical stimulations by a short train of electric pulses at 500 Hz was carried out through subdural electrodes located at the M1 (9 patients), S1 (3 patients), SMA (5 patients), and surrounding cortical areas, while surface EMG was recorded mainly from the muscles of the contralateral extremities. In 7 patients, ipsilateral muscles were also monitored. The current was given at 80 % of the intensity that produced clinical signs by 50Hz cortical stimulation. In 6 patients, the stimulation was carried out only in the resting condition. In the other 4 patients, the stimulation was carried out in both resting and contraction conditions., In the resting condition, the stimulation of M1 could evoke a motor evoked potential (MEP) in the contralateral muscles. The stimulation of SMA also could induce MEP in the contralateral muscles with longer latencies compared to the stimulation of M1. The stimulation of SMA did not evoke MEP in the ipsilateral muscles. In the contraction condition, the stimulation of M1 could evoke MEP followed by a silent period (SP) in the contralateral muscles. The stimulation of S1 (2 patients) could induce pure SP, without antecedent MEP. The stimulation of SMA could induce pure SP in one patient. In another patient, SP was recorded with antecedent MEP., The stimulation of SMA could evoke MEP in the contralateral extremities with longer latencies compared to the stimulation of M1. This fact may be useful for differentiation of M1 and SMA. The stimulation of S1 and SMA could induce pure SP, suggesting these cortical areas may be involved in the genesis of negative myoclonus., (Supported by the Japan Epilepsy Research Foundation.)