Circadian and homeostatic sleep regulation in morningness–eveningness

In subjects with intermediate circadian phases, the initial level and decay rate of slow-wave activity in NREM sleep were significantly higher in morning types than evening types.

• Morning and evening types exhibited similar circadian phases despite differing sleep timing preferences.
• Twelve morning-type and twelve evening-type subjects were categorized based on their dim light melatonin onset.
• In the intermediate phase group, morning types had greater slow-wave activity decay compared to evening types.
• No significant differences in slow-wave activity were found between extreme phase groups.
• There was no correlation between slow-wave activity decay and dim light melatonin onset.

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