Why Some Brains Refuse to Switch Off at Night

Many people experience the frustration of lying in bed exhausted, yet mentally wide awake. While the body feels ready for rest, the mind continues racing. New research suggests that this nightly struggle, common among individuals with chronic insomnia, may be linked not just to stress or anxiety but to a delayed and weakened internal brain clock.

New Research Sheds Light on Insomnia

A recent study titled Cognitive-affective disengagement: 24h rhythm in insomniacs versus healthy good sleepers, published in the journal Sleep Medicine, explores how the brain’s internal rhythm affects sleep patterns.

Conducted by researchers at the University of South Australia, the study found that people with chronic insomnia have a delayed and weaker “mental clock” compared to healthy sleepers. This mental clock refers to the 24-hour rhythm that regulates cognitive activity — influencing when the brain is alert and when it begins to wind down.

According to the findings, in individuals with insomnia, the shift from active, goal-directed thinking to quieter, dream-like mental states occurs much later than normal. As a result, their brains struggle to transition into sleep mode.

How the Study Was Conducted

To better understand this phenomenon, researchers observed 32 older adults — 16 with sleep-maintenance insomnia and 16 healthy sleepers.

Participants were monitored for 24 hours under strict “constant routine” conditions:

• Dim lighting throughout the day

• No napping allowed

• Controlled food intake

• Limited external time cues

Every hour, participants reported on their thoughts, describing their tone, structure, emotional quality, and how controllable they felt.

This design allowed researchers to isolate natural circadian rhythms without interference from environmental factors.

What Happens in Healthy Sleepers?

The study found that healthy sleepers display a clear and predictable daily mental rhythm.

During the afternoon, their thinking tends to be:

• Structured

• Logical

• Goal-oriented

• Grounded in reality

However, as night approaches, their cognitive style gradually shifts. Thoughts become:

• Less structured

• More image-based

• Dream-like

• Less focused on problem-solving

Researchers observed strong circadian patterns, with peak mental engagement occurring in the afternoon and a natural dip in the early morning hours. This gradual downshifting prepares the brain for sleep.

What Happens in People with Insomnia?

While individuals with insomnia also showed 24-hour rhythms, their patterns differed significantly.

1. Delayed Cognitive Peaks

Their peak mental activity occurred approximately 6.5 hours later than healthy sleepers. In practical terms, their brains continued daytime-style thinking well into the night.

2. Reduced Circadian Amplitude

The difference between daytime alertness and nighttime quietening was much smaller. Scientists describe this as reduced circadian amplitude — meaning the brain does not sufficiently “turn down” its activity at night.

3. Persistent Sequential Thinking

Insomniacs displayed higher levels of sequential thinking — logical, step-by-step chains of thought — particularly at night. This type of thinking keeps the brain actively engaged, making it difficult to drift into sleep.

In simple terms, their brains fail to downshift.

Is Insomnia Just Anxiety?

Anxiety levels were found to be higher in participants with insomnia. Anxiety is known to trigger sequential and repetitive thinking patterns. However, researchers caution against attributing insomnia solely to anxiety.

Instead, they suggest both insomnia and anxiety may share a neurological basis — particularly hyperactivity in the brain’s prefrontal cortex, the region responsible for planning, decision-making, and cognitive control.

This suggests that the problem may not be purely emotional, but biological. The brain may struggle to relinquish control when it is time to rest.

Understanding Cognitive Hyperarousal

Many insomnia sufferers describe experiencing a “racing mind.” Scientists refer to this as cognitive hyperarousal — a state where the brain remains alert and engaged when it should be disengaging.

The study proposes that hyperarousal may not simply stem from stress. Instead, it may be driven by a misaligned circadian rhythm that keeps cognitive systems active too late into the night.

Sleep, researchers note, is not just about closing one’s eyes. It requires the brain to detach from goal-directed thought and transition into a looser, more fluid mental state.

Can Strengthening the Body Clock Improve Sleep?

If insomnia is partly caused by delayed or weakened circadian rhythms, then therapies aimed at strengthening these rhythms may offer relief.

Researchers suggest several possible interventions:

• Timed bright light exposure in the morning

• Maintaining consistent daily routines

• Structured activity scheduling

• Mindfulness-based therapies

Mindfulness practices may be particularly helpful because they interrupt linear, chain-like thinking and encourage a non-judgmental awareness of thoughts — a mental state more conducive to sleep.

If future large-scale studies confirm these findings, treatments for insomnia could become more personalised, focusing on realigning the brain’s internal clock rather than merely suppressing symptoms.

Conclusion

This research highlights that insomnia may be more than stress or worry. A delayed and weakened mental clock could be keeping the brain active when it should be resting. By targeting circadian rhythms and cognitive patterns, future therapies may offer more effective solutions for millions struggling to switch off at night.