Excitability of the human motor cortex is enhanced during REM sleep.

A conspicuous feature of rapid eye movement (REM) sleep is atonia of postural muscles due to a powerful brainstem inhibitory effect on spinal motoneurones. However, small myoclonic jerks occur during REM sleep and increased activity of cortical neurones is suggested by the EEG. Transcranial cortical stimulation with magnetic pulses has been used to investigate motor excitability during sleep in man. Motor responses were evoked during sleep using stimuli identical to those used in wakefulness. Response amplitudes were depressed during slow wave sleep (SWS) and enhanced or the same during REM sleep. These findings suggest that the susceptibility of the human motor cortex to stimulation is enhanced during REM sleep.