Winter gloom and springtime glee are common seasonal swings. But beyond swaying how you feel, yearly cycles may also shift the way you think, according to a new study in the Proceedings of the National Academy of Sciences.

Comparing the cognitive function of 28 volunteers tested at different points in the year, researchers noted pronounced seasonal patterns in brain region activity. Namely, areas involved in working memory hit peak performance around the autumn equinox, and areas dealing with sustained attention crested around the summer solstice. Though it’s still early in the research to understand the significance of possible annual mental oscillations, the study hints at a previously unappreciated seasonal rhythm of the human brain that could affect learning and behavior.

For the study, researchers led by Pierre Maquet and Gilles Vandewalle at the University of Liège in Belgium recruited 28 healthy volunteers, split evenly by gender and all around 21 years old. To rule out the influence of daily rhythms and environmental factors, the researchers prepared the volunteers for the study by having them stay in the lab for 4.5 days. During this time, participants endured a 42-hour sleep deprivation routine in a dimly lit sound-proof room with no time cues.

After their daily senses were theoretically wiped clean and they got a full night’s sleep to recover, the volunteers underwent cognitive testing, completing a sustained attention task and a high-order executive function task. As the participants flexed their minds for the tests, researchers monitored their brain activity using functional magnetic resonance imaging (fMRI). This imaging data shows researchers which areas of the brain are active based on changes in blood flow, which is a proxy for fired-up nerve cell activity.

Examining the snapshots of brain activity, researchers noticed patterns of active brain areas that changed with the time of the year the participants were tested. Though the differences in brain activity didn’t seem to hinder the participants’ overall performances on the tests, the images suggest that different areas of the brain revved up to complete the tasks based on the season.

In particular, activity in areas of the brain involved in working memory, such as frontopolar areas, were most active in the fall and were closest to idle in the spring. For areas of the brain linked to sustained attention, such as the thalamus, activity peaked in the height of summer and dipped in the winter.

Next, the researchers will have to sort out biochemical changes and specific seasonal cues, such as temperature, humidity, and day length, that could help explain the patterns. And more work will be needed to understand if the patterns affect overall cognition and learning throughout the year.

Proceedings of the National Academy of Sciences, 2015. DOI: 10.1073/pnas.1518129113 (About DOIs).