Diurnal spectral EEG fluctuations in narcoleptic patients during rest and reaction time tasks

Abstract

Narcolepsy is associated with lowered vigilance. Diurnal variation in vigilance appears altered, but the exact nature of this change is unclear. It was hypothesized that the homeostatic sleep drive is increased in narcolepsy. Decreased levels of vigilance are reflected in low frequency band power in the electroencephalogram (EEG), so these frequencies were expected to be increased in the narcolepsy group. Furthermore, it was expected that low frequency power should increase over the day. Narcoleptic patients and healthy controls participated (36 participants in total); they were not allowed to take medication or naps on the experimental day. EEG was measured at 9:00, 11:00, 13:00, 15:00, and 17:00 hours, during rest and during reaction time tasks. In the narcolepsy group, alpha power was lower at rest at all times. Delta and theta power during rest and task performance increased steadily over the day in this group, from 11:00 hours onwards. Additionally, in the narcolepsy group beta1 and beta2 power during rest appeared increased at the end of the day. The effects in the lower frequency bands strongly suggest that vigilance is low at all times. The progressive increase in low frequency power indicates that the sleep drive is enhanced. It is not clear whether this pattern reflects an extreme state of low vigilance, or a pathological brain condition. The effects in the higher frequencies suggest that narcoleptic patients may make an effort to counteract their low vigilance level.