REVEALED: WHY SOME BRAINS REFUSE TO SWITCH OFF AT NIGHT

If you’ve ever lain awake with your thoughts racing while the rest of the house sleeps, new Australian research suggests the problem may not be willpower or worry, but timing.

A study led by the University of South Australia has found that chronic insomnia may be linked to disruptions in the brain’s natural 24-hour rhythm of mental activity, helping explain why some people struggle to mentally “power down” at night.

Published in the journal Sleep Medicine, the research is the first to map how cognitive activity rises and falls across the day in people with insomnia, compared with healthy sleepers.

THE MIND THAT WON’T SLOW DOWN

Insomnia affects around 10 per cent of the population and up to a third of older adults. Many describe the same experience: an overactive or racing mind when they should be winding down.

While this has long been associated with cognitive hyperarousal, it hasn’t been clear where those persistent thought patterns originate.

The new study set out to answer whether the problem lies deeper, in the brain’s internal clock.

INSIDE THE 24-HOUR BRAIN

Researchers monitored 32 older adults, half with chronic insomnia and half classified as healthy sleepers, over a full 24 hours of wakeful bed rest.

The tightly controlled laboratory conditions removed everyday cues like light, activity and routine, allowing scientists to observe the brain’s internal rhythms in isolation.

Participants remained awake in bed in dim lighting, with food and movement carefully regulated. Every hour, they completed detailed checklists assessing the tone, quality and controllability of their thoughts.

A RHYTHM THAT RUNS LATE

Both groups showed clear daily patterns in mental activity, with cognitive peaks in the afternoon and lows in the early morning. But the similarities ended there.

“Unlike good sleepers, whose cognitive state shifted predictably from daytime problem-solving to nighttime disengagement, those with insomnia failed to downshift as strongly,” said lead researcher Kurt Lushington.

“Their thought patterns stayed more daytime-like in the night-time hours when the brain should be quietening.”

The insomnia group’s cognitive peaks were also delayed by around six and a half hours, suggesting their internal clocks may actively promote alert, engaged thinking late into the night.

WHEN THE BRAIN CAN’T POWER DOWN

“Sleep is not just about closing your eyes,” Professor Lushington said. “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.”

NEW AVENUES FOR TREATMENT

Co-author Jill Dorrian said the findings point to new treatment possibilities that go beyond traditional behavioural approaches.

“These include timed light exposure and structured daily routines that may restore the natural day-night variation in thought patterns,” she said.

“Practising mindfulness may also help quieten the mind at night.”

The researchers say current insomnia treatments often focus on sleep habits and behaviour alone. Their findings suggest a more tailored approach, one that also targets circadian rhythms and cognitive activity, could offer relief for people whose minds simply won’t switch off.

The study, titled Cognitive-affective disengagement: 24-hour rhythm in insomniacs versus healthy good sleepers, appears in Sleep Medicine and was conducted by researchers from the University of South Australia, Washington State University and Flinders University.