Fig 1.
Study protocol to assess sleepiness following sleep restriction.
The protocol is plotted for a participant maintaining a 00:00–08:00 h sleep schedule (black bars). Following at least 3 weeks of an 8-hour sleep schedule at home, participants restricted their sleep to 5 hours on the last night at home, remaining in dim light for the 3 hours of extended wake (grey bar on study day 1). Participants attended the sleep laboratory on the following evening. Two hours after session start ambient light levels were reduced to < 2 lux (dark grey bar on study day 2). Saliva samples (●) were collected every 30 to 60 minutes for assessment of circadian phase. Sleep was further restricted to three hours duration in the laboratory (0 lux). POMS-Bi (+) was completed 1.75 hours after waking. Two hours after waking participants underwent constant posture (grey diagonal striped bar) and completed a performance battery (▲) including the Karolinska Sleepiness Scale, auditory psychomotor vigilance test, and Karolinksa Drowsiness Test. The test battery was practiced up to three times during constant posture on study night 1.
Table 1.
Participant characteristics shown for the entire sample (n = 43) and separately for individuals recording no lapses on the PVT (n = 16) compared to individuals with a high number of lapses (4+, n = 16) two hours after waking.
Fig 2.
Timing of melatonin onset (circles) for each participant (n = 43) relative to clock time (upper panel) and relative to sleep onset (phase angle of entrainment; lower panel).
Dashed line represents mean time of sleep onset and the triangle represents the mean melatonin onset time for all participants. A subset of these data (n = 28) has been published previously [24].
Fig 3.
Sleepiness measures two hours after waking following two nights of sleep restriction, as indicated by the number of PVT lapses (A & B; n = 43), Karolinska Sleepiness Scale (C & D; n = 43), and the proportion of EOG epochs containing slow eye movements (E & F; n = 37).
Data are plotted relative to circadian phase represented by (a) the clock hour of an individuals’ DLMO (left panels; A, C, E) and (b) phase angle difference between dim light melatonin onset (DLMO) and mean sleep onset on the 9 nights prior to the laboratory visit (right panels; B, D, F), (e.g., -2 represents someone with a DLMO occurring 2 hours before sleep onset time). Main bar plots represent data categorised into hourly bins (mean ± SEM) to illustrate the relationship between circadian phase and sleepiness. Inserts present the raw data scatterplots.
Fig 4.
Relationships between dim light melatonin onset and mood states composed-anxious (r = -0.366), agreeable-hostile (r = -0.347) and clearheaded-confused (r = -0.459).
All relationships were significant (p < 0.05). Higher values represent more positive mood.
Fig 5.
Schematic representation of the relationship between circadian phase and morning performance for individuals with a phase angle < 2 h (black) and individuals with a phase angle ≥ 2 h (grey).
Phase angle of entrainment represents the time between dim light melatonin onset (DLMO) and mean sleep onset on the 9 nights prior to the laboratory visit. Circles illustrate the timing of DLMO; horizontal bars represent sleep times; squares represent the number of PVT lapses two hours after waking.