Abnormal Reactivity of the ∼20-Hz Motor Cortex Rhythm in Unverricht Lundborg Type Progressive Myoclonus Epilepsy

Abstract

The ∼20-Hz component of the human mu rhythm originates predominantly in the primary motor cortex. We monitored with a whole-scalp neuromagnetometer the reactivity of the ∼20-Hz rhythm as an index of the functional state of the primary motor cortex in seven patients suffering from Unverricht–Lundborg type (ULD) progressive myoclonus epilepsy (PME) and in seven healthy control subjects. In patients, the motor cortex rhythm was on average 5 Hz lower in frequency and its strength was double compared with controls. To study reactivity of the ∼20-Hz rhythm, left and right median nerves were stimulated alternately at wrists. In controls, these stimuli elicited a small transient decrease, followed by a strong increase (“rebound”) of the ∼20-Hz level. In contrast, the patients showed no significant rebounds of the rhythm. As the ∼20-Hz rebounds apparently reflect increased cortical inhibition, our results indicate that peripheral stimuli excite motor cortex for prolonged periods in patients with ULD.