Physiological basis: how NREM sleep components can promote and REM sleep components can suppress seizure discharge propagation.

Objectives: To describe how the neural generators of different sleep components can provoke seizure discharge propagation during NREM sleep and can suppress it during REM sleep.

Methods: Experimental manipulations of discrete physiological components were conducted in feline epilepsy models (n=64), mostly in the systemic penicillin epilepsy model of primary generalized epilepsy and the amygdala kindling model of the localization-related seizure disorder, temporal lobe epilepsy. Procedures included seizure induction as well as quantifying norepinephrine concentrations (microdialysis) and the sleep-waking state distribution of seizures before and after lesions, systemic and localized drug administration and/or photic stimulation.

Results: (1) Neural generators of synchronous EEG oscillations, including tonic background slow waves and phasic 'arousal' events (sleep EEG transients such as sleep spindles, k-complexes), can combine to promote electrographic seizure propagation during NREM and drowsiness; anti-gravity muscle tone permits seizure-related movement. (2) Neural generators of asynchronous neuronal discharge patterns can reduce electrographic seizures during alert waking and REM sleep; skeletal motor paralysis blocks seizure-related movement during REM. (3) Etiology of the seizure disorder can interact with sleep and arousal mechanisms to determine sleep-waking state distribution of interictal and ictal events.

Conclusions: Differential effects of NREM versus REM sleep components on seizure discharge propagation are to some extent non-specific and in other ways specific to seizure etiology.