On-off intermittency of thalamo-cortical oscillations in the electroencephalogram of rats with genetic predisposition to absence epilepsy

Spike-wave discharges (SWD) are electroencephalographic hallmarks of absence epilepsy. SWD are known to originate from thalamo-cortical neuronal network that normally produce sleep spindle oscillations. Although both sleep spindles and SWD are considered as thalamo-cortical oscillations, functional relationship between them is still uncertain. The present study describes temporal dynamics of SWD and sleep spindles as determined in long-term EEG recordings in WAG/Rij rat model of absence epilepsy. It was found that non-linear dynamics of SWD fits well to the law of 'on-off intermittency'. Typical sleep spindles that occur during slow-wave sleep (SWS) also demonstrated 'on-off intermittency' behavior, in contrast to high-voltage spindles during intermediate sleep stage, whose dynamics was uncertain. This implies that both SWS sleep spindles and SWD are controlled by a system-level mechanism that is responsible for regulating circadian activity and/or sleep-wake transitions.