The suppressive effect of rapid eye movements during REM sleep on interictal epileptic discharges (IEDs): an intracerebral EEG study in two different type of epilepsy

Objectives: REM sleep is known to reduce epileptic activity. Here we test the hypothesis that phasic REM (P-REM) sleep has a higher suppressive effect on IEDs than tonic REM (T-REM), investigating the distribution of IEDs with intracerebral implanted electrodes (stereo-EEG), in drug resistant epileptic patients, across REM sleep. IEDs distribution was analyzed in two patient groups: a) with hippocampal sclerosis (HS) b) with focal cortical dysplasia (FCD). Methods: Night combining scalp-stereoEEG recordings were chosen. Sleep scoring was performed from scalp-EEG; P-REM and T-REM epochs were distinguished on the basis of eye movements-bursts (at least three in a 30 seconds epoch); moreover, eye-movements bursts (EM) were marked. Spikes were recognized with a semi-automated system on contacts recording from the HS and the FCD. Statistical analyses compared spike density in P-REM and T-REM and during EM and out of EM. Results: Nine recordings were analyzed (5FCD, 4MTS); 83.36 minutes of REM sleep were scored (66.53% P-REM, 34.47% T-REM; 50.1% time spent with EM). Spike rate (IEDs/min) was calculated for each condition. A signi fi cant reduction of IEDS was in found in P-REM with respect to T-REM (P < 0.05), with a percentage change of 33.35%. This variation resulted much higher, 74.16%, when comparing IEDs during EM and out of EM (P < 0.01). This behavior was confirmed also in the single groups (HS and FCD). Conclusion: Our data show that, independently from the histopathological substrate, REM sleep with EM exerts a stronger suppression effect on IEDs with respect to REM sleep without EM.