We all know that people's moods tend to vary with the seasons (you may have heard of Seasonal Affective Disorder (SAD) which comes with the beginning of winter). But few studies have looked at physiological fluctuations in the brain based on the time of year. A recent study carried out by a team at the University of Liège in Belgium shows that brain activity can vary according to the rhythm of the seasons. During what part of year are we most efficient?

To study the possible effect of the seasons on our brain activity, C. Meyer and her colleagues asked 28 subjects (14 men and 14 women; average age = 21 years) to remain in an environment devoid of any seasonal cues (such as brightness) over the course of four and a half days; this period included a phase of 50 hours of sleep deprivation. After this period of “confinement,” participants performed two cognitive tasks in order to evaluate their attention and working memory capacities. Functional MRI was used to scan the subjects’ brains. The protocol was used monthly between May 2010 and October 2011.

Brain imaging shows that for the sustained attention task, the maximal and minimal responses appeared respectively around the summer and winter solstices; while for the working memory task, the results were better in autumn and worse in spring. According to the authors, the differences in brain function aren’t noticeable in daily life, but they do show that brain activity changes throughout the year, and is likely influenced by the seasons.

Though the researchers can't yet determine which elements affect this "brain seasonality," they nevertheless suggest the following external factors: changes in temperature, humidity, amount of daylight, and even the length of social interactions. The meaning of these seasonal variations remains uncertain, as the number of participants was quite low.

Still, this study published in PNAS raises an interesting question about the possible effects of seasonality on human cognitive function.