Insomnia may be driven by delayed circadian rhythms that prevent the brain from powering down at night.
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.
Reference: “Cognitive-affective disengagement: 24h rhythm in insomniacs versus healthy good sleepers” by Kurt Lushington, Jillian Dorrian, Hans P.A. Van Dongen and Leon Lack, 25 October 2025, Sleep Medicine.
DOI: 10.1016/j.sleep.2025.106881
This study was internally funded by Flinders University of South Australia.
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7 Comments
I don’t understand why it’s so urgent for everyone to think they have to sleep at night the way I see it. The daytime is hot and bright and dusty where I live in Texas and the evening is cool and pleasant. That’s when I want to be awake and do my thinking. Why is it so ingrained that the entire population has to sleep during certain hours to be considered normal? It’s just foolish to put everybody in one box. Thank you. Enjoy your hot sweaty day. I choose to sleep during that brightness and congestion and smog and traffic and pollution. I like the cool crisp quiet night time air
I suffer from ADHD. It’s well know that we cannot quiet our minds. For over 35 years I’ve tried everything to no avail. The whole insomnia thing is far worse for people like me. It only gets worse with age.
They don’t take this into account In their studies.
I’ve tried every suggestion from diet, to changing lights colors and dimming based on time, to drugs and mindfulness. Absolutely nothing works. It’s not that simple to retrain a mind that races with a million thoughts. Especially if you have ADHD.
I’ve long ago just given in and sleep when my body and mind tells me to. To coin a phrase, “Resistance Is Futile”.
Tiring your mind until it’s totally fatigued is the ONLY solution I found that somewhat works. As in playing video games or engaging your mind into any activity that requires its complete attention and focus for long periods until it can’t cope anymore. This is what partially works for me.
Our circadian rhythm is distributed by our overactive minds and so our rhythm is different. I often find I function better at night anyway so sleep during part of the day.
This is just MY natural rhythm. I’ve never been a day person. I’m much more awake and functional during evening hours. Why should I fight against my body’s own clock to try to confirm to accepted societal norms. There are just those of us that are simply night owls and no amount of trying is going to fix it.
Though I’ve tried to put myself on a schedule, I always end up right back at my old nighttime life.
That’s just our natural rhythm.
Totally agree. I think most are hardwired from the time when there were no lights, you had to do your work during the day because night was dark. Just a suspicion, I don’t actually know but it makes sense.
Me too.
Im considered abnormal.
I appreciate the information, but it really doesn’t explain anything…”insomniacs” (like myself) have a different circadian rhythm…I think we all kinda already knew that. Is there an actual reason? Is there something we can change? What other info did the study find?
I guess we just have to find a sleep specialist to work with our individual needs??
I am a night person, as was my Mother. Some of us are just wired to be awake on a different schedule from most, and the best way to cope with it is to find work that allows one to maintain our natural body clock. My mom was forced into a day schedule by her psychiatrist, and I believe it led directly to her decline. Let those of us who do not conform to your schedule sleep when we need to.