Is Winter Good for Your Neurons?

It is that time of the year again. Whilst the Southern Hemisphere is coping with the sweltering heat of the summer, cold is sweeping across the rest of the globe, bringing with it snowfalls, violent winds, and an irresistible desire to spend most of your day curling up in bed. Winter is the named enemy of all summer lovers, and the bitingly cold months of this season have certainly contributed to its negative reputation. Musty parkas, questionable bubble hats, and runny noses are just some of the usual suspects of this season. And if this was not enough, a medical condition called darkness-induced seasonal affective disorder, or the winter blues, may explain the apparent link between winter and complex mood changes. Nonetheless, scientists are coming to realize that dark days may not be so dark after all.

The idea that our surrounding temperature affects the workings of our brain may seem far-fetched. However, new evidence suggests that temperature-related changes can sway your decision-making. Interesting studies have demonstrated that in particularly hot temperatures, we don’t actually make good decisions. Just a few months ago, Jose Cedeño-Laurent and colleagues examined differences in cognitive performance between students living in dormitories without air conditioning (AC) and those with AC. The study was conducted at the Harvard TH Chan School of Public Health during the 2016 Boston heat wave and aimed to disentangle the consequences of extreme heat on public health. Their findings indicated that students living without air conditioning displayed a 13.4% longer reaction time on cognition tests compared to their ‘cooler’ peers. In addition, students in rooms with AC not only appeared faster at answering, but were also more accurate. Although ticking the right box in a test can feel like a life-or-death experience, history teaches us that operating a quick and effective response in the battlefield can literally make the difference between life and death. So what happens when soldiers are faced with complex decisions under environmentally challenging conditions? This question intrigued a group of scientists at the Indian Armed Forces Medical College who assessed changes in cognitive performance in troops that had spent at least one year in desert conditions. Results were not good. Unsurprisingly, evaluation of attention, concentration, and memory all revealed a significant decline in hot climates, adding to the notion that high temperature can impair mental performance.

…the physical demands imposed by the cooling process in hot climates jeopardize brain functioning by depleting glucose more readily than in cold climates…

What about cold climates? One of the earliest studies to examine the apparent link between winter and cognition was carried out in Tromsø, Norway, where sixty-two participants were examined in a range of mental functions during winter and summer. In this study, subjects were found to display improved attention and shorter reaction times in the winter compared to summer months. These findings support the theory that lower temperatures enhance brain function and lead to improved decision making.

Yet, a heated (yes, that’s right) debate exists regarding the biological mechanisms of this presumed effect. One theory is that our body finds it more difficult to cool us down than to warm us up. Just like any other organ of the human body, our brain utilizes glucosa – a type of sugar found in foods that our body uses for energy – to fuel our mental processes. However, researchers found that more glucose is needed to cool us down than to warm us up, meaning that the physical demands imposed by the cooling process in hot climates jeopardize brain functioning by depleting glucose more readily than in cold climates. Conversely, it could be that more glucose is available to the brain in cooler environments, thus positively affecting our decision-making abilities.

Another possibility is that as the temperature decreases, neural activity becomes more ‘efficient’. This idea was recently put forward following a study in which 28 young men and women were asked to perform an attention and working memory task in a brain scanner at different times of the year. Results of this study indicated that mental performance does not vary significantly across seasons but, notably, brain activity was lowest in the winter and highest in the summer. This reduced winter brain activity was interpreted as a sign of improved efficiency as the brain was shown to perform equally well between summer and winter while consuming significantly less energy during the latter season.

Does all of the above mean that human beings are more prone to making poor decisions in warmer climates? And more importantly, will sticking your head in the refrigerator help you to ace exams?

While the above findings shine some light on the darkest season of the year, experimental evidence with regard to cognitive function in the cold is not always straightforward.

I am afraid the answer is no. While the above findings shine some light on the darkest season of the year, experimental evidence with regard to cognitive function in the cold is not always straightforward. Muller and colleagues at Kent State University used a computerized test battery to examine mental performance in young healthy men during periods of cold exposure or rewarming. Their data suggested that working memory and executive function decline relative to baseline when subjects are exposed to lower temperatures. This finding is intriguing as most studies suggest that cooler temperatures generally enhance mental activity. So where do these differences come from?

Some experts believe that mixed findings could be due to the duration or mode of cooling or the specific cognitive task adopted for the investigation. Indeed, it is important to remember that the exact impact of cold temperatures on cognitive function is still poorly understood, and therefore, the optimal temperature and duration of cooling to achieve measurable changes in brain function are yet to be established. Thus, longer exposures to cold temperatures or exposure to lower temperatures may differently influence the outcome of each study and thereby explain some conflicting results in the literature.

These discoveries suggest that the popular assumption that winter makes us sluggish and moody does not stand up to scientific scrutiny. In contrast, accumulating evidence suggests that your brain works better in the winter, entering what scientists call an ‘eco mode’ in which fewer resources are consumed to perform as well as in the summer. If you are one of those people experiencing winter blues, this refreshing discovery might help you to look at the darkest days of the year with a new, brighter light.

A neuron halfway between winter and summer season backgrounds. Illustrated by McCall Sarrett.

– Written by Marco Travaglio. Illustrated by McCall Sarrett.

  • Cedeño Laurent J.C., Williams A., Oulhote Y., et al. (2018). Reduced cognitive function during a heat wave among residents of non-air-conditioned buildings: An observational study of young adults in the summer of 2016, PLOS Medicine, doi: 10.1371/journal.pmed.1002605
  • Saini R., Srivastava K., Agrawal S., et al., (2017) Cognitive deficits due to thermal stress: An exploratory study on soldiers in deserts, Medical journal of Armed Forces of India, 73(4):370-374.
  • Muller M.D., Gunstad J., Alosco M.L., et al., (2012). Acute cold exposure and cognitive function: evidence for sustained impairment, Ergonomics, 55(7):792-8.
  • Meyer C., Muto V., Jaspar M., et al., (2016). Seasonality in human cognitive brain responses, Proceedings of the National Academy of Science U S A,113(11):3066-71.

Do you think that different seasons are influencing the way you think and work? Let us know in the comments below!

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Marco Travaglio

Marco Travaglio is currently pursuing a PhD in Neuroscience at The University of Cambridge. His research aims to generate novel mechanistic insights into the selective vulnerability of dopaminergic neurons in Parkinson’s disease. His project involves the use of both embryonic and induced pluripotent stem cell based model systems to study the onset of the disease and its subsequent pathological manifestations. He received his MSci in Neuroscience from the University of Nottingham.