Idiopathic Generalized Epilepsy: Magnetic Stimulation of Motor Cortex Time‐Locked and Unlocked to 3–Hz Spike‐and Wave Discharges

Summary: In 20 patients with idiopathic generalized epilepsy who showed typical 3‐Hz spike‐and‐wave (SW) EEG complexes, we studied the corticospinal motor output with a transcranial electromagnetic stimulator. First we measured the corticospinal discharge threshold for both hemispheres in the patient group and compared it with that of 10 ageand sex‐matched volunteers. Threshold was significantly higher in the patient group, regardless of whether subjects were treated with antiepileptic drugs (AEDs). In 4 patients with very frequent SW paroxysms, we were able to study motor evoked potential (MEP) changes time‐locked to epileptic EEG transients. The EEG signal was recorded bipolarly (C3–P3, C4–P4) by scalp needle‐electrodes. For a given stimulus intensity, we collected and measured MEPs occurring during the spike or the wave portion of the SW complexes. Data were compared with those of MEPs obtained time‐locked to normal EEG segments. MEP size was significantly decreased when the cortical stimulus was time‐locked to the wave component, and was decreased or unchanged when the stimulus was time‐locked to the spike. Magnetic stimulation never produced remarkable side effects.