Summary: People with chronic insomnia display a delayed and weakened daily rhythm of mental activity, leaving the brain in a more alert, daytime-like state during the night. In tightly controlled laboratory conditions, individuals with insomnia did not show the normal nighttime decrease in goal-directed thinking observed in healthy sleepers.
Their peak cognitive activity was shifted by roughly six and a half hours later than expected. These results indicate that insomnia can reflect a biological timing problem in how the brain disengages at night, not solely behavioral difficulty initiating sleep.
Key Facts
- Circadian Shift: Peak mental activity occurs several hours later in people with insomnia.
- Blunted Nighttime Shutdown: The normal reduction in cognitive engagement at night is reduced in insomnia.
- Treatment Implications: Strengthening circadian signals may help restore healthier sleep patterns.
Source: University of South Australia
Overview: Australian researchers report strong evidence that insomnia can be linked to disruptions in the brain’s 24-hour rhythm of cognitive and emotional activity. The findings help explain why some people find it difficult to “switch off” at night.
Published in the journal Sleep Medicine, the study led by the University of South Australia (UniSA) is the first to chart how cognitive-affective activity varies across the full day in older adults with chronic insomnia compared with matched healthy sleepers.
Insomnia affects roughly 10% of the general population and up to a third of older adults, many of whom report persistent, racing thoughts in the evening and overnight. Although this has commonly been described as cognitive hyperarousal, the biological origins of those persistent thought patterns have been unclear.
To test whether nighttime cognitive hyperactivity stems from circadian irregularities, researchers used a constant routine protocol. Thirty-two older adults—16 with chronic sleep-maintenance insomnia and 16 healthy sleepers—spent 24 hours in wakeful bedrest under dim light, with meals and activity strictly controlled. This method removes normal environmental and behavioral time cues so internal rhythms can be observed directly.
Participants completed an hourly checklist that measured the tone, quality and controllability of their thoughts, as well as the degree of goal-directed or emotional involvement in their thinking. The checklist captured both the content and metacognitive aspects of mentation across the 24‑hour period.
Both groups showed clear circadian patterns in mental activity, with daytime peaks and early-morning troughs. Crucially, however, people with insomnia differed in three main ways: their nighttime decline in cognitive engagement was less pronounced, their overall day–night variation in several thought qualities was smaller, and their peak cognitive activity was delayed by approximately six and a half hours.
“Good sleepers demonstrate a predictable shift from active, goal-oriented thinking during the day to disengagement at night,” says lead researcher Professor Kurt Lushington (UniSA). “Participants with insomnia did not show that same downshift; their thoughts remained more daytime-like during night hours when the brain should be quieting.”
This diminished and delayed disengagement suggests the brain’s internal clock may be signaling wake-like cognitive states later into the night. The authors interpret the findings as supporting the hyperarousal model of insomnia in which prefrontal and goal-directed processing remain active when they should be reduced.
Co-author Professor Jill Dorrian (UniSA) notes the clinical implications: “Current therapies often emphasize behavioral strategies for sleep initiation. Our data suggest that interventions aimed at strengthening circadian rhythms—such as well-timed light exposure and consistent daily routines—could help restore the natural day–night variation in thinking. Mindfulness and techniques to reduce sequential, goal-focused thought at night may also be beneficial.”
Key Questions Answered
Q: Why does the mind stay active at night in people with insomnia?
A: The internal circadian timing of cognitive-affective activity in people with insomnia appears to fail to downregulate normally, leaving the brain in a more alert, daytime-like state during night hours.
Q: Is insomnia linked to disrupted circadian rhythms?
A: Yes. In this study, rhythms of mental activity in insomniacs were both delayed and reduced in amplitude compared with healthy sleepers.
Q: Does the brain ever quiet in insomnia?
A: The brain does show reductions in activity, but these occur later and less robustly than in good sleepers.
Editorial Notes
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full.
- Additional contextual information was added by editorial staff.
About this research
Author: Candy Gibson, University of South Australia
Source: University of South Australia
Contact: Candy Gibson, University of South Australia
Image credit: Neuroscience News
Original Research: Open access. “Cognitive-affective disengagement: 24-hour rhythm in insomniacs versus healthy good sleepers” by Kurt Lushington et al., published in Sleep Medicine.
Abstract
Cognitive-affective disengagement: 24-hour rhythm in insomniacs versus healthy good sleepers
This study investigated whether a failure to down-regulate cognitive-affective activity at night in people with insomnia reflects underlying circadian rhythm abnormalities. Sixteen sleep-maintenance insomniacs (11 female; mean age 64.3 ± 7.2 years) and 16 good sleepers (11 female; mean age 65.4 ± 7.4 years) completed a constant routine protocol involving 24 hours of wakeful bedrest to control for conditioned responses to sleep initiation.
Participants filled out an hourly cognitive-affective disengagement checklist that included items assessing the tone and quality of mentation and items assessing metacognitive control. Cosinor analyses tested circadian rhythmicity and group differences.
Most measures demonstrated clear circadian rhythms in both groups. However, compared with good sleepers, insomniacs showed smaller 24‑hour variation (reduced amplitude) in reality orientation (dream-like vs real-like mentation), volitional control (degree of control over mental activity), and thought structure. Insomniacs also showed a higher average level of sequential, goal-oriented thinking at night, consistent with continued cognitive engagement.
These results align with the hyperarousal model of insomnia: a failure to downregulate prefrontal cognitive processing at night leads to more goal-directed thought and less cognitive-affective disengagement. Strengthening circadian rhythmicity and reducing sequential thinking at night are proposed as potential avenues for future insomnia interventions.