How the seasons affect our brains

While the notion that celestial bodies affect our personalities and human affairs has no scientific basis, the planet’s orientation toward the sun does. Another way of putting it? Astrology isn’t real, but seasonal changes affect our moods and even our cognition.

Seasonal affective disorder or, SAD, is the most widely known affliction showing the influence the seasons have on our brains. It’s characterized by recurrent clinical depression, and it particularly affects people in northern latitudes, where seasonal amounts of daylight vary more than they do nearer the equator.

Scandinavians in particular experience SAD in large numbers and go to what may seem like extremes to combat it: many undergo light therapy, but one town in Norway installed mirrors to direct light into the valley where they lived, because the sun never rose above the surrounding mountains during the depths of winter. If this sounds like overkill, consider that there is a strong correlation between depression and cognitive impairment. Attention, memory and information processing are all impacted negatively by depression, and according to one study, the cognitive effects of depression haven’t been well treated with antidepressants. So it makes sense that people might go to great lengths to prevent seasonal depression before it sets in.

Cognition in winter isn’t just mood-dependent either. People in general tend to be ‘smarter’ in summer and fall than they are in winter and spring. That is, in one study older adults performed so much better on neuropsychological tests during warmer months that it translated to a 4.8 year cognitive-age difference. This difference was particularly noticeable when it came to working memory and speed of perception. While this seasonal discrepancy might not seem like a big deal—after all, a few months would theoretically bring you back up to snuff—the same study showed that people were 24% more likely to be diagnosed with cognitive impairments including Alzheimer’s Disease if they were tested in winter or spring. Seasonal changes in cognition can have long-term implications.

Scientists still have only a partial understanding of the biological mechanisms behind brain health’s seasonal variations. Serotonin levels, which are closely associated with mood, appear to fluctuate with the seasons. There is also seasonal oscillation of gene expression and even blood cell composition, with upwards of 5,000 genes being expressed more strongly in different seasons. Not only do these changes create many potential ways to impact cognitive function, but the immune system is markedly more prone to inflammation in the winter and shows increased risk for “cardiovascular, psychiatric and autoimmune diseases.”

Scientists know these changes are seasonal and not, say, due to temperature changes because they don’t occur at different points in the day (ie. morning vs. night) and because they persist even when people are tested during sensory deprivation of seasonal signals. And, as expected, there is an inversion of the seasonal cognitive pattern when researchers looked at countries in the southern hemisphere so that Australian summer (December - March) yields better mood and cognition. So, while a “snowbird” retiree’s seasonal move from, say, New York to Florida probably won’t quite do the trick, it seems like actual migratory birds may be onto something…. Christmas in Argentina, anyone?

By Aimee Fountain

References:

https://www.theatlantic.com/health/archive/2017/03/seasonal-affective-disorder-mosaic/519495/

https://www.alzforum.org/news/research-news/does-cognition-change-seasons

https://www.health.harvard.edu/blog/sad-depression-affects-ability-think-201605069551

https://www.nature.com/articles/ncomms8000

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4449160/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3202491/

https://neurosciencenews.com/seasonal-affective-disorder-1515/

https://pubmed.ncbi.nlm.nih.gov/8401963/

https://pubmed.ncbi.nlm.nih.gov/26858432/

https://pubmed.ncbi.nlm.nih.gov/30180184/

https://www.sciencedirect.com/science/article/abs/pii/S0165178117302615