It is well known that our body's circadian rhythm controls our sleep cycle, but we also have what are called ultradian rhythms, which may not only influence daily activity but the onset of mental illness as well, according to a new study.

Our daily sleep-wake cycle is governed by an internal 24-hour timer. But ultradian rhythms, on the other hand, which are usually overlooked, follow a much shorter, four-hour cycle. This may explain why, on average, we eat three meals a day that are relatively evenly spaced across our daily wake period.

"Usually superimposed on the 24-hr diurnal or circadian rhythm, ultradian oscillations have been observed in the context of locomotion, sleep, feeding, body temperature, serum hormones, and brain monoamines in species ranging from fruit flies to humans," wrote the research team, from the Douglas Mental Health University Institute and McGill University.

So what causes these shorter cycles? According to the researchers, the answer is dopamine - a key chemical substance in the brain that is often associated with motivation or pleasure. When dopamine levels are out of whack, it disrupts ultradian rhythms, making them last for as long as 48 hours.

This is important considering that previous research has suggested that imbalanced dopamine levels play a part in causing bipolar disease and schizophrenia, two types of mental illness.

What this new study, published in the journal eLife, argues is that a structured schedule with regularly established meal times and early bedtimes may lead to a better life and perhaps even prevent the onset of mental illness.

To better understand ultradian rhythms, lead researcher Dr. Kai-Florian Storch and his colleagues conducted a study on genetically modified mice. They found that an imbalance of an ultradian rhythm generator (oscillator) based on dopamine causes sleep abnormalities, rather than disruption in circadian rhythm as was previously thought.

These findings can possibly explain the symptoms of mania - periods of excitement or euphoria - and depression often observed in certain bipolar patients. That is, when the ultradian arousal oscillator goes awry - running on a 48-hour cycle instead of a four-hour cycle - sleep becomes disturbed and mania will be induced in bipolar patients.

This research could potentially lead to breakthrough treatments for bipolar disorder and other forms of mental illness that are affected by the body's dopamine levels.

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