Average global temperatures have risen by more than one degree since the industrial revolution, and whilst this may seem small, it is resulting in more and more extreme weather events such as flooding, storms and heatwaves. With sweltering temperatures of 34 degrees already being reached across Cambridge this summer, intense heat is threatening to become the new normal. The physical damage caused by storms and flooding is obvious, but how does heat impact our ability to think?

We’ve all been there: imprisoned in a hot, stuffy library, staring blankly down at a problem sheet or a particularly opaque journal article, unable to think of anything but the muggy air promising to suffocate you. But is your sheer lack of brain power simply due to a lack of motivation, or a genuine stress response?

“Unlike the rest of the body, which can use the evaporation of sweat to cool down, the brain relies only on blood flow carrying heat away”

Our brain is extremely sensitive to heat. Unlike the rest of the body, which can use the evaporation of sweat to cool down, the brain relies only on blood flow carrying heat away, making it more vulnerable in hotter weather. This effect is further exacerbated if dehydration results in these dilated blood vessels transporting less blood.

Several studies have looked at the neurological response of brains to heat. In an article from the Journal of Neuroinflammation using mice kept at a temperature of 43 degrees, this was quantified and explained through exploring the effects of neuroinflammation and neurodegeneration. Whilst the human brain is undoubtedly larger and more complex than that of a mouse, the individual neuron types and connections are similar.

“Participants in buildings with no air conditioning were shown to have up to a 10% decrease in cognitive performance”

Neuroinflammation occurs when the glial cells in our nervous system become ‘activated’ due to applied stress. Glial cells are like the ‘bodyguards’ to neurons in our central nervous system, offering support and protection. When we are in hot environments and our body is placed under stress, these glial cells release inflammatory enzymes, such as iNOS (inducible nitric oxide synthase) and cyclooxygenase-2, which produce highly reactive free radicals and compounds such as prostaglandins that cause pain. When too many of these enzymes are produced, neurodegeneration can occur, causing neuronal death and loss of synaptic proteins.

These inflammatory molecules can also interfere with the production of new neurons in the hippocampus part of the brain, resulting in reduced memory formation and slower brain processing. Another study from the PLOS Medicine journal confirmed this result – this time using a sample of 44 humans during a heatwave. Participants in buildings with no air conditioning were shown to have up to a 10% decrease in cognitive test performance.

Your brain feeling like porridge may, in fact, be explained by the hot weather. But can it also account for your lack of motivation?

Data from a study conducted in Switzerland by Marvin Bundo would suggest so. Based on 906 participants, the study found the probability of having a bad mood for an entire day increased by 7% for each five degree temperature increase. This result can be explained by considering the neurotransmitters – or ‘chemical messengers’ – dopamine, serotonin and noradrenaline that are involved in temperature regulation. For instance, noradrenaline can cause the contraction of blood vessels, which reduces heat loss to the surroundings. But these neurotransmitters are also involved in regulating mood: dopamine is involved in learning and reward, serotonin affects sleep and anxiety, and noradrenaline manages stress responses. It follows that heat-induced changes in the balance of these neurotransmitters can result in mood swings, irritability and an overwhelming desire to not do your work.

So next time you just can’t concentrate in the college library, rather than calling yourself lazy, perhaps it’s time to invest in a fan.