EEG Spectral Analysis of the Sleep-onset Period in Narcoleptics and Normal Sleepers

The sleep-onset period of 10 drug-free patients with narcolepsy-cataplexy and 10 normals matched for age and gender was investigated using the multiple sleep latency test to elicit episodes of intentional sleep onset. Spectral analyses were calculated for delta, theta, alpha, sigma, and beta frequencies using 5-second epochs beginning at lights-out and continuing until the first 2 minutes of stage 2 or REM sleep were reached, or until 20 minutes had elapsed. The sleep-onset period was divided into quartiles, and mean root mean square (RMS) amplitude within each quartile was calculated. Mean delta amplitude was significantly higher across the sleep-onset period of narcoleptic REM naps and narcoleptic stage 2 naps compared to the sleep-onset period of normal stage 2 naps or normal stage 1 naps. Mean theta amplitude was significantly higher for narcoleptic REM naps compared to normal stage 1 naps, and tended to be higher for narcoleptic stage 2 naps compared to normal stage 1 naps. Mean alpha amplitude was significantly lower for narcoleptic REM naps and narcoleptic stage 2 naps compared to normal naps containing just stage 1. Mean sigma amplitude was significantly lower for narcoleptic REM naps compared to normal stage 1 naps, and tended to be lower for narcoleptic REM naps compared to normal stage 2 naps. Mean beta amplitude did not differ between the narcoleptic and normal sleep-onset process. These findings support the existence of electrophysiologic differences within the microstructure of the process of sleep entry in narcoleptics and normals.