Abstract:
Several recent studies have described the period of impaired alertness and performance
known as sleep inertia that occurs upon awakening from a full night of sleep. They report that
sleep inertia dissipates in a saturating exponential manner, the exact time course being task
dependent, but generally persisting for one to two hours. A number of factors, including sleep
architecture, sleep depth and circadian variables are also thought to affect the duration and
intensity. The present study sought to replicate their findings for subjective alertness and reaction
time and also to examine electrophysiological changes through the use of event-related potentials
(ERPs). Secondly, several sleep parameters were examined for potential effects on the initial
intensity of sleep inertia.
Ten participants spent two consecutive nights and subsequent mornings in the sleep lab.
Sleep architecture was recorded for a fiiU nocturnal episode of sleep based on participants'
habitual sleep patterns. Subjective alertness and performance was measured for a 90-minute
period after awakening. Alertness was measured every five minutes using the Stanford Sleepiness
Scale (SSS) and a visual analogue scale (VAS) of sleepiness. An auditory tone also served as the
target stimulus for an oddball task designed to examine the NlOO and P300 components ofthe
ERP waveform. The five-minute oddball task was presented at 15-minute intervals over the initial
90-minutes after awakening to obtain six measures of average RT and amplitude and latency for
NlOO and P300. Standard polysomnographic recording were used to obtain digital EEG and
describe the night of sleep. Power spectral analyses (FFT) were used to calculate slow wave
activity (SWA) as a measure of sleep depth for the whole night, 90-minutes before awakening and
five minutes before awakening.
