Sydney: Biological clocks of humans, animals and even plants are intricately linked with day and night. But when they fall out of sync, they have potentially damaging consequences.

Swinburne University of Technology researcher Greg Murray, who has keenly studied the body clock or the circadian system, found its rhythms can impact human mood.

His research has linked the body clock and certain psychological responses, including the capacity to trigger relapses in patients with bipolar disorder.

Mood disorders such as bipolar disorder have long been linked with sleep problems, suggesting that the circadian system plays a role in these conditions.

"If you take seriously this idea that the body clock is part of a causal pathway to mood disorders, then a natural deduction is that monitoring clock function might provide early warning of relapse in vulnerable people," Murray said.

Murray and his PhD student Ben Bullock have just tested the theory in a project funded by the National Depression Initiative. Twelve volunteers with bipolar disorder were fitted with wrist-worn devices designed to monitor their circadian system by measuring their physical activity throughout the day and night.

According to Murray, these actigraphs give a usable measure of circadian output under natural conditions.

The subjects were tracked for up to 12 months. During the period, one participant experienced a serious relapse that landed him in hospital. "For our purpose, it was very interesting that circadian activity data really did show a marked signal of deterioration in the days and even weeks before the relapse."

Instead of his activity patterns operating on a 24-hour cycle, the participant shifted to a 48-hour cycle of wakefulness and broken, disturbed rest.

"With Indic Premananda, from the University of Massachusetts, we are analysing the actigraph data to find the time scale at which rhythm disruption is most apparent," Murray said.

In the next stage of research, the team wants to see if signals of rhythm disruption in patients can be used as markers of vulnerability to bipolar disorder in the general population. IANS