Sleep increases firing rate modulation during interictal epileptic activities in mesial structures

Abstract

Epileptic seizures and interictal epileptiform discharges (IEDs) are strongly influenced by sleep and circadian rhythms. However, human data on the effect of sleep on neuronal behavior during interictal activity have been lacking. We analyzed EEG data from epileptic patients implanted with macro and micro electrodes targeting mesial temporal structures. Sleep staging was performed on concomitantly recorded polysomnography and video-EEG. Automated IED detection identified thousands of IEDs per patient. Both the rate and amplitude of IEDs were increased with deeper stages of NREM sleep. Single unit activity (SUA) and multi-unit activity (MUA) increased their firing during the IED spike, and strongly decreased during the subsequent slow wave. These time-locked firing rate modulations were shown to increase during deeper stages of NREM sleep. Finally, during resting behaviour, neuronal firing rate, bursting rate and firing regularity were all shown to progressively decrease with deeper stages of NREM sleep.