Chronotype and diurnal patterns of positive affect and affective neural circuitry in primary insomnia

Evening-types with insomnia exhibit a reduced degree of diurnal variation in the metabolism of brain regions associated with positive affect.

• Chronotypes differ in daily patterns of self-reported positive affect and brain region activity.
• Evening-types show a phase delay and smaller amplitude in positive affect compared to morning-types.
• Diurnal variation in metabolism is lower in the medial prefrontal cortex and striatum for evening-types.
• Overall metabolism in positive affect-related brain regions is lower in evening-types during both morning and evening wakefulness.
• Alterations in brain activity may help explain the increased risk of mood disorders in evening-type insomniacs.

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