Just as the leaves fall or the sunlight hours rise, you brain could have an internal rhythm tied to the pattern of the seasons, according to a study recently published in Proceedings of the National Academy of Sciences.

Researchers from the University of Liege in Belgium looked at the cognitive brain processes of 28 fit and young individuals at different times throughout the year. The subjects were invited to and maintained in the lab for four-and-a-half days before the tests, away from seasonal cues such as sunlight levels, and exposing them to artificially constant light and temperature levels. This was to “acclimatize” the volunteers and ensure that they weren’t influenced by environmental factors, but rather something more internal and ingrained.

While being given two separate attention and working memory tasks, their brain activity was recorded through an fMRI scan.

Interestingly, while their test scores remained the same throughout the year, many of the participants' brain waves seemed to follow a seasonal pattern. The levels of brain activity on the attention task peaked in June and was lowest in December. As Live Science explains, these are points near to the summer solstice and the winter solstice, respectively. Conversely, brain responses during the memory test were highest in the autumn and lower around spring.

The findings suggest that, depending on the season, different areas of the brain have to work harder to sustain certain cognitive functions. Essentially, the researchers say that the physiology of the brain may change to compensate for the season, which could be related to differing levels of calorie intake.

Far from being the result of external factors, such as the physical effect of the weather on the body, the Belgian scientists suggest these patterns are more like an internal seasonal clock. This could have perhaps developed among early humans, giving them an evolutionary advantage by helping them cope with varying external factors.

“Humans were very dependent on seasons a few thousand years ago so it is not surprising to see seasonality in humans as in most species,” the study authors said.

While these are interesting observations, New Scientist points out that the team currently has no insight as to how this process could happen. Additionally, while the subjects were given a few days to get used to an “aseasonal” external environment, it’s more or less impossible to completely remove all external sense of season.