Reduction of transcallosal inhibition upon awakening from REM sleep in humans as assessed by transcranial magnetic stimulation.

STUDY OBJECTIVES

The aim of the study is to assess, in humans, transcallosal inhibition upon awakening from rapid eye movement (REM) and non-REM sleep, by paired-pulse transcranial magnetic stimulation (TMS).

DESIGN

During the daytime, a baseline session of motor evoked potentials (MEPs) was recorded. During the nighttime, the TMS sessions were administered just before sleep onset and upon awakenings from REM and stage 2 sleep, both in the early and final part of night.

SETTING

The sleep research laboratory at the University of Rome "La Sapienza."

PARTICIPANTS

Ten right-handed subjects participated in the experiment for 4 consecutive sleep-recording nights.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

During the daytime, a robust transcallosal inhibition was found; the MEP amplitude reduction ranged from 35% to 40%. During the nighttime, a decrease of transcallosal inhibition from right-to-left motor cortex, as compared to that from left-to-right motor cortex, was observed. The direct assessment of MEP changes, as a function of sleep stage and of the time of night, pointed to a drop of transcallosal inhibition after awakening from REM sleep. Therefore, the inhibitory activity of transcallosal fibers observed after non-REM awakening almost disappeared after REM sleep awakenings.

CONCLUSIONS

The drastic drop of transcallosal inhibition after awakenings from REM sleep represents the first evidence in humans of a change of interhemispheric connectivity mediated by the corpus callosum during this sleep stage and may open new avenues for a better understanding of some aspects of sleep mechanisms (ie, dreaming function and dream mentation).