NEW STUDY SHOWS WHY SOME MINDS CAN’T SWITCH OFF AT NIGHT

Insomnia affects about 10 per cent of the population,

For anyone who has lain awake watching the hours tick by, the idea of a “racing mind” at night will feel painfully familiar.

Now, Australian researchers say they have uncovered why some brains simply refuse to power down at bedtime.

A new study has found compelling evidence that insomnia may be linked to disruptions in the brain’s natural 24-hour rhythm of mental activity, offering fresh insight into why switching off at night can feel impossible for some people.

Published in Sleep Medicine, the research was led by the University of South Australia and is the first to map how cognitive activity rises and falls across the day in people with chronic insomnia, compared with healthy sleepers.

Insomnia and the overactive mind

Insomnia affects about 10 per cent of the population, rising to as many as one in three older adults.

Many people with the condition describe an overactive or “racing” mind at night, a symptom long associated with cognitive hyperarousal.

Until now, it has remained unclear where these persistent thought patterns originate.

Researchers set out to determine whether the inability to downregulate mental activity at night, a hallmark of insomnia, reflects deeper abnormalities in circadian rhythms, the internal biological clock that governs sleep-wake cycles.

Inside the 24-hour brain experiment

Under tightly controlled laboratory conditions, 32 older adults were monitored over 24 hours of wakeful bed rest.

The group included 16 people with chronic insomnia and 16 healthy sleepers.

By eliminating environmental and behavioural cues such as light changes, movement and normal daily routines, researchers were able to isolate the brain’s internal rhythms.

Participants stayed awake in a dimly lit room, remained in bed, and had food and activity carefully regulated. Every hour, they completed checklists assessing the tone, quality and controllability of their thoughts.

Clear rhythms, striking differences

Both healthy sleepers and people with insomnia showed clear circadian patterns in mental activity, with peaks in the afternoon and troughs in the early morning.

But crucial 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.”

The study also found that cognitive peaks in people with insomnia were delayed by about 6.5 hours, suggesting their internal clocks may be driving alertness well into the night.

Why the brain won’t power down

According to Professor Lushington, sleep is about far more than simply closing your eyes.

“Sleep is not just about closing your eyes,” he 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.”

New directions for treatment

Co-author UniSA Professor Jill Dorrian says the findings open the door to new treatment approaches that go beyond traditional behavioural strategies.

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

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

The researchers argue that while many current treatments focus solely on behaviour, tailored approaches that address both circadian rhythms and cognitive activity could offer more effective relief for people with insomnia.

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