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11:18:55 
2026-03-28 
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Australian scientists have uncovered strong evidence that chronic insomnia may stem from disruptions in the brain’s internal 24-hour cycle of mental activity. The findings help explain why some people find it so difficult to “switch off” at night, even when they are physically tired.
In a study published in Sleep Medicine, researchers from the University of South Australia (UniSA) tracked how thinking patterns rise and fall across the day in people with long-term insomnia compared with healthy sleepers. This is the first study to chart daily cognitive rhythms in this way.
Insomnia affects roughly 10% of the population and up to one-third of older adults. Many people with the condition describe their minds as overactive or constantly racing at night.
Although this nighttime mental alertness has often been described as cognitive hyperarousal, its underlying cause has remained uncertain. The researchers set out to test whether difficulty calming the mind at night, a defining feature of insomnia, might be linked to abnormalities in circadian rhythms, the body’s internal timekeeping system.
Removing the world to reveal the clock
To investigate this, the team conducted a carefully controlled laboratory experiment involving 32 older adults, including 16 with insomnia and 16 without sleep problems. Participants were monitored for 24 hours while remaining awake in bed. By removing external time cues and daily routines, the researchers were able to focus specifically on the brain’s natural internal rhythm.
Volunteers stayed in a dimly lit environment with tightly regulated food intake and activity levels. Every hour, they completed detailed checklists describing the tone, quality, and controllability of their thoughts, allowing researchers to map how mental activity changed throughout the day and night.
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 nighttime 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.
When disengagement is delayed
“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.
“Practicing mindfulness may also help quiet the mind at night.”
The researchers say that current treatments often focus on behavioral strategies, but these findings suggest that tailored approaches addressing circadian and cognitive factors could offer a solution.
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