Summary: People with chronic insomnia show a delayed and weakened daily rhythm of mental activity, keeping the brain in a more alert, daytime-like state at night. Under tightly controlled conditions, individuals with insomnia failed to show the normal nighttime drop in goal-directed thinking seen in healthy sleepers.
Their peak cognitive activity also shifted roughly six and a half hours later than normal. These findings suggest insomnia involves a biological timing problem in how the brain powers down, not just behavioral difficulty falling asleep.
Key Facts
- Circadian Shift: Mental activity peaks occur hours later in people with insomnia.
- Blunted Nighttime Shutdown: The expected drop in cognitive engagement during night is reduced.
- Treatment Implications: Strengthening circadian rhythms may improve sleep outcomes.
Source: University of South Australia
Australian researchers have found compelling evidence that insomnia may be linked to disruptions in the brain’s natural 24-hour rhythm of mental activity, shedding light on why some people struggle to ‘switch off’ at night.
Published in Sleep Medicine, the study led by the University of South Australia (UniSA) is the first to map how cognitive activity fluctuates across the day in individuals with chronic insomnia, compared to healthy sleepers.
Insomnia affects about 10% of the population, and up to 33% of older adults, with many reporting an overactive or ‘racing’ mind at night.
While this has long been linked to cognitive hyperarousal, it has remained unclear where these thought patterns stem from.
Researchers examined whether the inability to downregulate mental activity at night – a hallmark of insomnia – reflects underlying circadian rhythm abnormalities.
Under tightly controlled laboratory conditions, 32 older adults were monitored (16 with insomnia and 16 healthy sleepers) over 24 hours of wakeful bedrest.
This approach eliminated environmental and behavioural cues, allowing scientists to isolate the brain’s internal rhythms.
Participants remained awake in a dimly-lit room, in bed, with food and activity carefully controlled. They completed hourly checklists, assessing the tone, quality and controllability of their thoughts.
Both healthy sleepers and insomniacs showed clear circadian patterns in mental activity, with peaks in the afternoon and troughs in the early morning.
However, several key differences emerged in the insomnia group.
“Unlike good sleepers, whose cognitive state shifted predictably from daytime problem-solving to nighttime disengagement, those with insomnia failed to downshift as strongly,” says lead researcher UniSA Professor Kurt Lushington.
“Their thought patterns stayed more daytime-like in the night-time hours when the brain should be quietening.”
Their cognitive peaks were also delayed by around six and a half hours, suggesting that their internal clocks may encourage alert thinking well into the night.
“Sleep is not just about closing your eyes,” Prof Lushington says. “It’s about the brain disengaging from goal-directed thought and emotional involvement.”
“Our study shows that in insomnia, this disengagement is blunted and delayed, likely due to circadian rhythm abnormalities. This means that the brain doesn’t receive strong signals to ‘power down’ at night.”
Co-author, UniSA Professor Jill Dorrian, says the findings highlight new treatment possibilities for insomniacs, such as interventions that strengthen circadian rhythms.
“These include timed light exposure and structured daily routines that may restore the natural day-night variation in thought patterns,” Prof Dorrian says.
“Practising mindfulness may also help quieten the mind at night.”
The researchers say that current treatments often focus on behavioural strategies, but these findings suggest that tailored approaches addressing circadian and cognitive factors could offer a solution.
Key Questions Answered:
A: Their brain’s internal clock fails to properly reduce cognitive activity during nighttime hours.
A: Yes. Mental activity rhythms are delayed and weakened compared to healthy sleepers.
A: It does, but much later and less effectively than in healthy sleepers.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this insomnia and circadian rhythm research news
Author: Candy Gibson
Source: University of South Australia
Contact: Candy Gibson – University of South Australia
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Cognitive-affective disengagement: 24-hour rhythm in insomniacs versus healthy good sleepers” by Kurt Lushington et al. Sleep Medicine
Abstract
Cognitive-affective disengagement: 24-hour rhythm in insomniacs versus healthy good sleepers
This study explored whether a failure to down-regulate cognitive-affective activity at night in insomniacs reflect the presence of underlying circadian rhythm abnormalities. 16 sleep maintenance insomniacs (11 F; 64.3 ± 7.2 y) and 16 good sleepers (11 F; 65.4 ± 7.4 y) participated in a constant routine protocol involving 24 h of wakeful bedrest, which controls for any conditioned response to sleep initiation.
Every hour participants completed a cognitive-affective disengagement checklist containing four items assessing the tone and quality of mentations and four items assessing metacognitive activity.
Circadian rhythmicity and group differences were tested using cosinor analyses. Except for thought modality (mental activity was auditory vs imagery) and thought structure (mental activity was repetitive vs sequential) in insomniacs, the remaining tone and quality of mentations and all metacognitive measures demonstrated circadian rhythmicity in both insomniacs and good sleepers.
However, insomniacs compared to good sleepers demonstrated less 24 h variation (smaller amplitude) in reality orientation (mental activity was dream-like vs real-like), volitional control (little vs much control over mental activity) and thought structure; and reflective of continuing cognitive engagement, a greater tendency for sequential mental activity at night (higher mesor).
Our findings are consistent with the hyperarousal model of insomnia, with the failure to downregulate prefrontal activity at night leading to greater goal-oriented processing and less cognitive-affective disengagement.
Strengthening the circadian rhythmicity of cognitive-affective activity and modifying sequential thinking are potential interventions in the future treatment of insomnia.
