Those working through the night or regularly falling victim to jet lag may be familiar with the physical toll of disrupting our biological clocks. Progress has been made in understanding how our bodies can better adjust to these disruptions, but scientists have now discovered a "reset button" that could lead to new possibilities for treatments to get our bodies back in sync.

Our biological clocks, or circadian rhythms, run on 24 hour cycles and are dictated by changes in light. If an external factor throws this clock out of whack, be it through lack of exposure to sunlight, working late shifts or playing World of Warcraft all night, it can induce depression, changes in mood and conditions such as seasonal affective disorder.

Over the years, various research efforts have been directed at pinning down the mechanism that keeps this clock ticking, and how it might be manipulated to counter the negative health impacts. This has resulted in solutions such as LED light glasses, purpose-built glass houses and glowing pillows.

Now, researchers from Tennessee's Vanderbilt University claim to have discovered a switch for the brain's master biological clock. The study was conducted using genetically modified mice, which the researchers say possess an almost identical biological clock to humans, other than being nocturnal.

"We found we can change an animal’s sleep and wake rhythms by artificially stimulating the neurons in the master biological clock, which is located in an area of the brain called the suprachiasmatic nucleus (SCN), with a laser and an optical fiber," says Douglas McMahon, Professor of Biological Sciences at Vanderbilt University.

This optogenetics technique sees genes expressing optically sensitive proteins inserted into particular cells with the aim of changing how they respond to light. The team found that in doing so, they could both stimulate and suppress the activity of the SCN neurons to replicate night and day and actually force the clock to reset. The firing rate of these neurons had previously been thought to be only an output of the biological clock's activity.

"Of course, this exact approach isn’t ready for human use yet," says Michael Tackenberg, a doctoral student who worked on the study. "But others are making progress toward eventually using optogenetics as therapy."

Tackenberg is now investigating whether the mice with seasonal affective disorder respond to the new technique.

The research was published in the journal Nature Neuroscience.

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