Imagine this: the sun is shining, it’s warm, birds are chirping, bees are buzzing, the cold days of winter have ceased and a new season has just begun. Every year, we as humans gravitate (almost as a herd) toward warmth and more social interaction. These repetitive behaviors have been ingrained in our biology since the dawn of time; even the tiniest organisms rely on the sun and the Earth’s yearly revolutionary path. Each passing day brings our planet a step closer to another season and subsequent adjustments in organism behavior, such as hibernation during the winter and spending time in the sun during the summer. These subtle changes in our environment and eventual shifts of the seasons are not only shaping our behavior but more astonishingly, our brains!  

Photograph of the back of a woman sitting in a sunny, grassy field
A woman enjoying the sunshine (Image source: Pixabay)

The plastic and moldable features of our brain and behavior are sensitive to environmental stimuli. For example, if you touch a hot stove, it’s extremely unlikely you’ll do it again. The brain is made up of cells called neurons that transmit electrical and chemical molecules between particular areas of the brain that are necessary to execute precise behaviors. These neurons communicate with each other through gaps called synapses, which are crucial for learning. The malleability of those synapses is called plasticity, a type of adaptation that allows for our brains to respond to complex events, environments, and experiences.

Adaptation is essential for our survival and longevity, especially for extreme weather in our climate. A group of researchers found interest in this connection between weather and how the brain responds. Using a large dataset of brain images, they explored the effects of our environment on brain size and volume. They found that changes in the weather, such as extreme heat, barometric pressure, and humidity, can predict the volume of your brain. In other words, as the seasons change, so does your brain!

This observation was accomplished using brain imaging with a functional magnetic resonance imaging (fMRI) machine, which allows for direct measurements of volume for particular regions of interest (ROIs). They gathered about 12,600 images over 15 years from 3000 subjects. Pressure, temperature, and humidity on the days these images were collected were used as predictors of brain volume for many structures, including the cortex, cerebellum, amygdala, thalamus, and hippocampus. All of these structures are essential for our daily behaviors, including memory, navigation, and movement. Astonishingly, these investigators found that specific structures and areas of the brain change in volume as the seasons change

In particular, the volume of areas involved in movement, such as the cerebellum, was found to be negatively associated with pressure, such that as barometric pressure decreased, the volume increased. In the winter months, there is less barometric pressure in the environment, which in combination with less movement during winter results in a smaller cerebellum. Moreover, this trend was similar for deep brain (or “subcortical”) ROIs, indicating that subcortical volume decreases during the summer months compared to the winter months. These results point to an adaptive response within our brain that limits unnecessary energy expenditure for structures used less often during different times of the year.

Miniscule differences from one day to the next are likely not observable, however, this research demonstrates the ability to observe brain changes over time that were previously unknown and unobserved. Even further, these results point to a potential influence from underlying biological factors, such as changes in blood flow, oxygen levels, and levels of vitamins that may also fluctuate with the seasons.

As our brains and body adapt to the environment and changes in the seasons, they unfortunately also have the potential to leave us sensitive to disease. Both psychiatric and biological illnesses have been linked to changes in the seasons, such as seasonal affective disorder and multiple sclerosis. However, using brain imaging and exploring related hypotheses, it may be possible to pinpoint specific brain-related impairments that are associated with these illnesses (or previously unknown diseases that could be seasonally influenced). Moreover, these impairments can then be utilized in individualized treatment protocols to potentially alleviate the deficits of a devastating disease. 

In summation, our brains are plastic to our environment (that is, a good kind of plastic!) Our behavior has adapted to the seasons, which may actually be changing the shape of our brain. This leaves us a significant opportunity to approach seasonality as a potential catalyst in every area of medicine, neuroscience, and behavioral science. 


Peer edited by Maria Cardenas

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