Y. Harrison et Ja. Horne, OCCURRENCE OF MICROSLEEPS DURING DAYTIME SLEEP ONSET IN NORMAL SUBJECTS, Electroencephalography and clinical neurophysiology, 98(5), 1996, pp. 411-416
The main aim of this study was to explore whether the multiple sleep l
atency test (MSLT) could be made more sensitive to low daytime sleepin
ess in normal, healthy subjects by adopting a shorter period of sleep
(microsleep) as a sleep onset criterion. Subjects underwent MSLTs unde
r two conditions: after normal (baseline) nighttime sleep, and after n
ighttime sleep extension (creating a 'floor effect' of minimal daytime
sleepiness). MSLT sleep onset thresholds of 5 s (microsleeps), 30 a (
the norm) and 90 s of sustained sleep gave 3 separate sleep latency sc
ores for 240 MSLT trials derived from 10 subjects. With low daytime sl
eepiness, whether this be in the morning after baseline sleep or throu
ghout the day after sleep extension, the 5 s sleep onset criterion was
a more sensitive measure of sleepiness than the established 30 s crit
erion. This was the case both for sleep onset latency and for the freq
uency of sleep onsets. Spectral analyses of the EEG indicated that suc
cessive microsleep episodes generally became more substantial, and, de
pending on the level of sleepiness, culminated in more overt signs of
sleep. There was little difference between the 30 s and 90 s criteria
for sleep onset latency scores, although there was a small but signifi
cant difference between them in the frequency of sleep onsets. As dayt
ime sleepiness increased, particularly in the afternoon and under base
line, the 5 s criterion reached a ceiling, with the 30 s criterion bec
oming more sensitive.