The Transcranial Magnetic Stimulation (TMS) as a new research tool in psychphysiology of sleep.

TMS is now an established technique in neurosciences allowing the noninvasive assessment of cortical excitability, but its system- atic application to sleep has been limited by the fact that delivering a single suprathreshold stimulus awakens subjects, or lightens their sleep. We have used TMS in three different protocols: (1) motor thresholds (MTs) to assess corticospinal excitability upon REM and NREM awakenings; (2) cortico-cortical paired pulses to as- sess intracortical facilitation and inhibition in REM and SWS; (3) inter-hemispheric paired pulses to assess callosal inhibition in REM and NREM sleep. The main findings are (1) an increase of MTs in REM sleep reflecting the brainstem inhibitory effect on spinal motoneurons [Bertini et al., J Sleep Res 13:31–6, 2004]; (2) a heightened cor- tical facilitation in REM sleep than in SWS and wakefulness [De Gennaro et al. Eur J Neurosci 19:3099–104, 2004]; (3) a drop of callosal inhibition in REM sleep [Bertini et al. Sleep 27:875–82, 2004]. The coherent pattern of empirical results encourages the psychophysiological study of the corticospinal organization in different sleep stages, legitimating the introduction of TMS as a new tool for sleep research.