Scientists have found evidence that our brains are most active during the summer, with the warmer months appearing to help ramp up the neurological activity required during attention and memory tests.
This seasonal difference in the way the brain functions was apparent, even though participants were being kept in dim light conditions for days before they were tested. This suggests that the brain is relying on an 'internal clock' rather than daylight cues.
Before you drop all your classes and sign up for summer school, we need to make it clear that the study is based on the results of just 28 people, so there's definitely room for further investigation.
And the participants didn't actually get better test results in summer when compared to winter - what the study measured instead was how active people's brains were during these tests. But that's interesting because it's some of the first research into how the seasons can affect our cognitive function, and it provides solid early evidence that such a link exists.
To figure out how our brains change throughout the year, researchers from the University of Liege in Belgium recruited 28 young, healthy volunteers, and tested them every month with two different cognitive tasks - one of the tests measured their attention span, and one measured their working memory, which refers to the amount of information the brain can store and process over a short amount of time.
To make sure the results weren't influenced by external cues, the participants were kept in a dimly lit room for four and a half days before being tested, where they were deprived of external cues. (Side note: that sounds like a pretty terrible way to spend your summer holidays, so thanks for taking one for the team, brave volunteers.)
The volunteers were all hooked up to functional MRI (fMRI) machines throughout the tests, which allowed the researchers to see how their brains were functioning throughout the year.
Although the test results didn't differ significantly based on the season, the participants' brains all seemed to be more sluggish in the colder months.
During the attention tests, brain activity was highest around the summer solstice (the longest day of the year), and was lowest at the time of the winter solstice (the shortest day of the year).
When it came to working memory, the cognitive function peaked at the autumn equinox, which is when the length of the day and night is nearly (but not quite) equal. In the Northern Hemisphere, this occurs around September 22 to 24. The lowest cognitive function when it came to working memory was around the time of the spring equinox.
"Brain responses to both tasks varied significantly across seasons, but the phase of these annual rhythms was strikingly different, speaking for a complex impact of season on human brain function," the researchers report in the Proceedings of the National Academy of Sciences.
We already know that the seasons can affect people's mood, but this is some of the first evidence to suggest that our changing brain activity may play a role in that.
The researchers suggest that the phenomenon may be a throw-back to the days when our ancestors would have been a lot more active in summer, compared to winter, and so their brains may have evolved to reflect that trend.
"Humans were very dependent on season a few thousand years ago so it is not surprising to see seasonality in humans as in most species," lead researcher Gilles Vandewall told The Telegraph. "The mechanism may therefore be a remnant of ancestral rhythmicity."
There are still a lot of questions to be answered - right now scientists really don't know how the seasons could be affecting our brain's performance, particularly given that the link appears to be independent of light.
"Many seasonally changing factors could regulate such a pattern, including day length (known as photoperiod), temperature, humidity, social interaction and physical activity," writes Sam Wong for New Scientist. "Since these weren't all controlled for in the study, it's impossible to say what is responsible for the seasonal changes seen."
Research last year showed that different genes are activated across the seasons, but the mechanism behind the link is something that will need to be investigated further.
So for now, let's take some solice in the fact that there may actually be a scientific reason that, for many of us, everything - including thinking - is more of a struggle in winter.