Study Links Insomnia to Disruption of Brain's Internal Clock

Published in Sleep Medicine, this research is notable for being the first to track cognitive rhythms throughout the day in individuals with chronic insomnia compared to healthy sleepers. Insomnia impacts around 10% of the population and as much as a third of older adults, many of whom describe experiencing racing thoughts during the night.

Previously characterized as cognitive hyperarousal, the cause of this heightened nighttime mental activity remained unclear. The study aimed to explore whether the inability to relax at night, a core characteristic of insomnia, is linked to abnormalities in circadian rhythms, the body’s internal clock.

In a controlled laboratory setting, the team monitored 32 older adults—16 with insomnia and 16 without—in an environment stripped of external time cues. They remained awake in bed while their food intake and activity levels were strictly regulated. Participants completed hourly checklists evaluating their thought tone, quality, and controllability to observe fluctuations in mental activity over the course of 24 hours.

Both groups demonstrated clear circadian patterns, with peaks in cognitive activity in the afternoon and troughs early in the morning. However, important distinctions emerged within the insomnia group. Unlike healthy sleepers, who showed a predictable transition from daytime cognitive engagement to nighttime quietness, insomniacs failed to decrease their mental engagement effectively in the evening hours.

Lead researcher, Prof. Kurt Lushington, noted that the thought patterns of those with insomnia remained more active at night compared to healthy individuals, suggesting their cognitive peaks were delayed by approximately six and a half hours. This implies that the internal clocks of insomniacs may promote alertness late into the night.

Prof. Lushington emphasized that sleep involves not just closing one’s eyes but also disengaging the brain from active thinking and emotional engagement. The study found that this disengagement in insomniacs is weaker and delayed, likely due to abnormal circadian rhythms, leading to insufficient signals for the brain to wind down.

Co-author Prof. Jill Dorrian discussed potential treatment avenues that could help insomniacs, such as interventions designed to strengthen circadian rhythms through timed light exposure and organized daily routines that restore natural cognitive variations associated with day and night. Mindfulness practices may also assist in quieting the mind at night.

The researchers pointed out that while current treatments often focus on behavioral approaches, their findings suggest that customized strategies targeting both circadian and cognitive factors could enhance treatment effectiveness.

The study, titled “Cognitive-affective disengagement: 24h rhythm in insomniacs versus healthy good sleepers,” was published on October 25, 2025, and is internally funded by Flinders University of South Australia.