CANBERRA, 28th November, 2025: A new study from Australian researchers has uncovered a potential reason why some people find it difficult to mentally switch off at night, linking insomnia to disruptions in the brain’s natural 24-hour rhythm of cognitive activity. The findings, published in Sleep Medicine, mark a significant step toward understanding how the internal body clock influences mental rest and wakefulness. The research, led by the University of South Australia (UniSA), is the first to chart fluctuations in thought patterns over a full day among people with chronic insomnia compared with healthy sleepers. Insomnia affects around 10 percent of the global population and up to one-third of older adults, many of whom report persistent, racing thoughts that prevent restful sleep.
Although this phenomenon has long been tied to a state of cognitive hyperarousal, the biological basis behind it has remained largely unknown. To investigate, scientists conducted a 24-hour laboratory study involving 32 older adults, half of whom had chronic insomnia. Participants were kept under tightly controlled conditions, awake and in bed within a dimly lit environment. Meals, posture, and external cues such as light and activity were strictly regulated. Every hour, subjects completed detailed checklists evaluating the tone, quality, and controllability of their thoughts, allowing researchers to measure mental activity independent of environmental influences. Both healthy participants and those with insomnia exhibited clear circadian patterns in their mental activity, peaking during the afternoon and declining in the early morning.
Findings offer pathway to restore healthy sleep cycles
However, the insomnia group showed a notably weaker shift between daytime engagement and nighttime mental rest. According to lead researcher Professor Kurt Lushington of UniSA, this failure to transition reflects a fundamental disturbance in how the brain aligns cognitive rhythms with the sleep-wake cycle. “Unlike good sleepers, whose cognitive states naturally shift from problem-solving during the day to disengagement at night, those with insomnia do not downshift as effectively,” Professor Lushington explained. “Their thought processes remain more daytime-like, with elevated mental activity persisting into hours when the brain should be quietening.”
He added that the study revealed delayed cognitive peaks by roughly six and a half hours in participants with insomnia, suggesting that their internal clocks may be misaligned toward later-night alertness. “Sleep is not just about closing your eyes,” Lushington noted. “It involves the brain actively disengaging from goal-oriented and emotionally charged thinking. Our findings indicate that this disengagement is both blunted and delayed in those with insomnia, possibly due to circadian rhythm abnormalities that prevent the brain from receiving strong cues to power down.” Co-author Professor Jill Dorrian emphasized that the research opens new avenues for treatment beyond traditional behavioural therapies. “Approaches that strengthen circadian rhythms could help,” she said. “Timed light exposure, consistent daily routines, and mindfulness practices may encourage the natural rise and fall of mental activity across the day.”
Circadian rhythm therapy could redefine insomnia care
The researchers concluded that while existing therapies often focus on managing sleep-related behaviours, addressing the interplay between circadian timing and cognitive patterns may yield more effective long-term solutions. By identifying how disrupted internal rhythms sustain an overactive mind, the study provides a clearer understanding of insomnia’s biological underpinnings and offers a foundation for future interventions aimed at restoring the brain’s natural capacity to rest, improving overall mental health, emotional balance, and daily cognitive performance. – By Content Syndication Services.