EEG desynchronization during phasic REM sleep suppresses interictal epileptic activity in humans

Area of Science:

• Neuroscience
• Sleep Medicine
• Epileptology

Background:

• Rapid eye movement (REM) sleep is known to suppress epileptic activity.
• Cholinergic neurotransmission during REM sleep may mediate this suppression through neuronal desynchronization.
• Interictal epileptiform discharges (IEDs) and high-frequency oscillations (HFOs) are key biomarkers of the epileptogenic zone.

Purpose of the Study:

• To investigate the distribution of IEDs and HFOs during phasic and tonic REM sleep.
• To test the hypothesis that IEDs are more suppressed during phasic REM sleep due to increased cholinergic drive.

Main Methods:

• Polysomnography with combined scalp-intracerebral electroencephalography (EEG) in 12 patients.
• Identification of phasic REM (with rapid eye movements) and tonic REM (without rapid eye movements) sleep stages.
• Analysis of intracerebral EEG for power in specific frequency bands, IEDs, ripples (>80 Hz), and fast ripples (>250 Hz) in the seizure-onset zone (SOZ), irritative zone (EIZ), and normal zone (NoZ).

Main Results:

• Lower power in frequencies <30 Hz during phasic REM sleep, indicating increased desynchronization.
• Significantly reduced frequency of IEDs, ripples, and fast ripples during phasic REM sleep compared to tonic REM sleep (p < 0.001).
• Increased abundance of physiologic ripples in the normal zone during phasic REM sleep, while epileptogenic zone ripples decreased.

Conclusions:

• Phasic REM sleep exhibits a stronger suppressive effect on IEDs, supporting the role of EEG desynchronization in suppressing epileptic activity.
• The increase in physiologic ripples during phasic REM sleep may be associated with REM sleep functions like memory consolidation and dreaming.