Magnetoencephalographic analysis of cortical myoclonic jerks.

We studied the pre-myoclonus spike using magnetoencephalography in patients with cortical myoclonus (6 with cortical reflex myoclonus and one with epilepsia partialis continua). The spike was estimated as a single current dipole on the pre-central gyrus in one patient with epilepsia partialis continua. In contrast, it was estimated as a single dipole on the post-central gyrus in 5 of 6 patients with cortical reflex myoclonus, and as two dipoles on the pre- and post-central gyrus in the remaining patient. We conclude that there are 3 physiological types of cortical myoclonus: (1) abnormal discharges in the motor cortex produce the myoclonus; (2) the source of the myoclonus is mainly the sensory cortex; (3) both the motor and sensory cortices play important roles in the production of myoclonus.