Abnormal reactivity of the similar to 20-Hz motor cortex rhythm in Unverricht Lundborg type progressive myoclonus epilepsy

The similar to 20-Hz component of the human mu rhythm originates predominan tly in the primary motor cortex, We monitored with a whole-scalp neuromagne tometer the reactivity of the similar to 20-Hz rhythm as an index of the fu nctional 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 o n average 5 Hz lower in frequency and its strength was double compared with controls. To study reactivity of the similar to 20-Hz rhythm, left and rig ht median nerves were stimulated alternately at wrists. In controls, these stimuli elicited a small transient decrease, followed by a strong increase ("rebound") of the similar to 20-Hz level. In contrast, the patients showed no significant rebounds of the rhythm. As the similar to 20-Hz rebounds ap parently reflect increased cortical inhibition, our results indicate that p eripheral stimuli excite motor cortex for prolonged periods in patients wit h ULD. (C) 2000 Academic Press.