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How Your Brain Knows When It’s Summer: Circadian Clock Linked To Seasons And Length Of Day

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Seasons have quite the influence on our moods and bodies — making us hungrier, sadder, and more fatigued in the cold months and more energetic and happy in the warmer months.

We’ve all experienced or at least heard of seasonal affective disorder (SAD) — which typically occurs when it gets dark at 4 p.m. and we want to hole up in our rooms — but can also occur during the humid summer months. It’s rather frustrating that a change in weather can have such a profound effect on our minds and emotions.

Researchers out of the RIKEN Brain Science Institute in Japan have examined how humans and animals keep track of seasons on a physiological level. They hope that their new findings can eventually help develop treatments for people who suffer from SAD.

“Just like in other animals, our bodies keep track of the seasons,” Jihwan Myung, an author of the study, said in the press release, “and sudden changes in seasonal day length can cause severe mood disorder in some individuals. Understanding how to adjust our internal seasonal clock could lead to effective ways of helping people whose internal clocks have been disrupted.”

Their study focuses on a circadian clock of sorts that’s located in the brain, which tracks changes in daylight through neurotransmitters. This part of the brain also monitors our circadian rhythm — which is responsible for making us tired when it’s dark, and more awake when the sun rises. It’s called the suprachiasmatic nucleus (SCN).

The SCN expresses certain “clock” genes throughout a 24-hour period — and two of its regions aren’t entirely synched, the authors note. When days get longer in the summer, the gap between the two brain regions widens too. Assuming this was an explanation for why our moods change with the season, the researchers delved into how this occurs; they refer to the two SCN regions as dorsal and ventral, and the “clock” gene as BMAL1.

The researchers focused on mice and found that mice living during long “summer” days had out-of-phase BMAL1 levels in dorsal and ventral regions, while those from shorter days were in synch. This might be caused by a neurotransmitter called GABA, which typically inhibits neurons, but in this case activates neurons due to high levels of chloride in the neurons. When GABA activity was inhibited by the researchers, the gap between dorsal and ventral regions closed.

Ultimately, the researchers believe that inhibiting GABA could have an impact on regulating our brain changing significantly during seasonal changes. If it’s further researched, the researchers hope that it can be used to move SAD treatments forward.

By Lecia Bushak