Daytime vigilance in chronotypes: Diurnal variations and effects of behavioral sleep fragmentation

Mar 25, 2008Behavioural brain research

Daytime alertness in morning and evening types: daily changes and impact of disrupted sleep

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Abstract

Vigilance levels in 12 morning types and 12 evening types showed significant diurnal variations across multiple measures, except for the psychomotor vigilance task.

Diurnal variations in vigilance were observed for subjective alertness, waking EEG recordings, and sleep latency tests.
Sleep fragmentation led to decreased vigilance levels in all measures, apart from the psychomotor vigilance task.
The effects of sleep fragmentation and recovery were similar for both morning and evening types.
Extreme chronotypes exhibited differences in diurnal variations of subjective alertness and sleep latencies, while intermediate chronotypes showed identical patterns.
No major differences in response to sleep fragmentation were found across chronotype subgroups.

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Vigilance levels of 12 morning types (M-types) and 12 evening types (E-types) were investigated after a baseline night, 2 nights of sleep fragmentation (5 min of forced awakening every half-hour) and a recovery night. Sleep timing was adjusted to the preferred sleep schedule of each subject. Daytime vigilance levels were assessed with test series including a scale of subjective alertness, a psychomotor vigilance task (PVT), a waking EEG recording, and a sleep latency test. Test series were administered every 4h, beginning 1.5h after wake time. On the baseline day, significant diurnal variations were found for each vigilance measure, except for the PVT. Diurnal variations were similar in M-types and E-types. Sleep fragmentation decreased vigilance levels on each measure, except the PVT. Effects of sleep fragmentation and recovery were similar in the two chronotypes. These results highlight the similarities in diurnal variations of vigilance in the two chronotypes when studied at their preferred sleep schedule. Results were also compared between chronotypes with extremely early or late circadian phases ("Extreme" subgroup) and between those with similar, intermediate circadian phases ("Intermediate" subgroup). Diurnal variations of subjective alertness and sleep latencies differed between "Extreme" chronotypes but were identical between "Intermediate" chronotypes. There were no major differences in the response to sleep fragmentation in any subgroup. Since phase angles differed by the same amount between chronotypes within each subgroup, the results suggest that a difference in phase angle cannot be the only source of the differences observed in diurnal variations between "Extreme" chronotypes.

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Daytime vigilance in chronotypes: Diurnal variations and effects of behavioral sleep fragmentation

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