A new American study sheds light on the role of certain neurons that allow the brain to adapt to differences in the duration of light exposure during seasonal changes. This would explain in particular the “seasonal depression”.
- During the winter period, the days are short and the luminosity less intense: it would go from 100,000 lux (unit of measurement of luminosity) on sunny summer days to sometimes barely 2,000 lux on winter days.
- Seasonal depression, or seasonal affective disorder, is depression related to lack of natural light. In Europe, it concerns 1.3 to 4.6% of the population.
- Exposing yourself to as much daylight as possible and eating enough omega-3 fatty acids would prevent low morale and motivation, whatever the time of year.
Duration of exposure to light according to the seasons – longer days in summer, shorter in winter – has long been associated with behavioral changes. Sleep, eating habits, brain and hormonal activity, everything is turned upside down.
The example of seasonal depression
Seasonal depression is a good example. This type of depression, linked to reduced exposure to natural light, usually occurs during the winter months and is much more common in countries in the far north, such as in Scandinavia, where the hours of sunshine are the most. short. The light therapy has been shown to be an effective remedy for treating seasonal depression. But until now we didn’t really understand the mechanism that causes these mood swings.
Everything happens at the level of neurons
According to one new studypublished in Science Advances, this would happen at the level of certain neurons. Researchers at the University of California, San Diego were able to shed light on this process using mice. They found that in response to variations in day length, certain neurons change the way key neurotransmitters interact with each other. Which would then trigger behavioral changes and altered brain activity.
The role of the suprachiasmatic nucleus
These neurons are nestled in the hypothalamus, the part of the brain involved in regulating important functions like hunger, thirst, sleep, sexual behavior or emotions. Specifically, in a small structure called the suprachiasmatic nucleus (SCN), made up of about 20,000 neurons. The SCN is the body’s timekeeper: it regulates most of the circadian rhythms – the physical, mental, and behavioral changes that follow a 24-hour cycle. The SCN works through light-sensitive cells in the retina that communicate changes in light and day length to our body. Given its role, the SCN could become a promising target for new treatments for disorders associated with seasonal variations in light exposure.