Study reveals why people with insomnia cannot stop thinking at night

Scientists from the University of South Australia have announced solid evidence uncovering why individuals with insomnia struggle to stop their thoughts during the night.

The findings show that a disruption in the brain’s natural 24-hour rhythm of mental activity is the main reason the brain loses its ability to shift from active daytime thinking to the calm state required at night.

According to the researchers, this is the first study of its kind to map fluctuations in cognitive activity throughout the day in individuals with chronic insomnia, compared to healthy sleepers.

Under strictly controlled laboratory conditions, 32 older adults—16 with insomnia and 16 healthy—were monitored for 24 hours while lying in bed but kept awake. This approach allowed scientists to isolate the brain’s internal rhythms.

Both healthy participants and those with insomnia displayed clear rhythmic patterns of cognitive activity, peaking in the afternoon and reaching their lowest levels in the early morning.

However, several key differences emerged in the insomnia group.

Professor Kurt Lushington, the lead researcher, explained:

> “Unlike good sleepers, whose cognitive state predictably shifts from daytime problem-solving to mental disengagement at night, people with insomnia fail to make this transition with the same strength. Their thinking patterns remain similar to daytime levels during night hours when the brain should be winding down.”

He added that sleep is not simply about closing one’s eyes; it requires the brain to detach from goal-directed thinking and emotional engagement.

The study reveals that this mental disengagement is weaker and delayed in people with insomnia, likely due to disturbances in their circadian rhythm. This means the brain does not receive strong signals to “switch off” at night.

Insomnia refers to difficulty falling asleep or staying asleep, which leads to daytime fatigue. It can be short-term (non-chronic) or chronic and has negative effects on both physical and mental health.

Symptoms include difficulty initiating sleep, frequent awakenings, very early morning wake-ups, daytime tiredness, and trouble concentrating.

Insomnia can also contribute to health issues such as high blood pressure, obesity, and depression.