As heatwaves become more intense with climate change, scientists are racing to understand how extreme heat changes the way our brains work.

When Jake was five months old, he had his first tonic-clonic seizure, his little body stiffening and then jerking rapidly. "It was extremely hot, he had overheated and we witnessed what we thought would be the scariest thing we would ever see," says his mother, Stephanie Smith. "Unfortunately, it wasn't."

Seizures began to crop up often in hot weather. As soon as the stifling, humid days of summer would arrive, the family would resort to all kinds of cooling methods and a fierce battle to keep the seizures at bay would ensue.

Following a genetic test at the age of 18 months, Jake was diagnosed with Dravet Syndrome, a neurological condition that includes a form of epilepsy and affects around one in 15,000 children. Seizures are often accompanied by intellectual disability and a range of comorbidities such as autism and ADHD, as well as difficulties with speech, mobility, eating and sleep. Heat and sudden temperature changes can bring on a seizure.

Jake is now 13 years old, but has endured countless seizures with the turn of the weather, his mother says. "Increasingly hot summers and heatwaves are adding to the burden of living with this already devastating condition," says Smith.

Dravet Syndrome is just one of many neurological diseases that are exacerbated by higher temperatures, says Sanjay Sisodiya of University College London and a pioneer in the field of climate change's impact on the brain. A neurologist who specialises in epilepsy, he frequently heard from patients' families that they had more troubles during heatwaves. "And I thought to myself, of course, why shouldn't climate change also affect the brain? After all, so many processes in the brain are involved in how the body copes with heat."

As he dug into the scientific literature, he discovered a range of neurological conditions that are made worse by rising heat and humidity, including epilepsy, stroke, encephalitis, multiple sclerosis, migraine, along with a number of others. He also discovered that the effects of climate change on our brains are already becoming visible.

During the 2003 European heatwave, for example, about 7% of the excess deaths involved direct neurological problems. Similar figures were also seen during the 2022 UK heatwave.

But heat can also alter other ways our brains function – making us more violent, grumpy and depressed. (Find out more about how heatwaves warp the mind in this article by Zaria Gorvett.)

So, as the world warms due to climate change, what can we expect the effect on our brains to be?

The human brain is, on average, rarely more than 1C (1.8F) higher, on average, than our core body temperature. Yet our brains – as one of the more energy-hungry organs in our bodies – produce a fair amount of their own heat when we think, remember and respond to the world around us. This means our bodies have to work hard to keep it cool. Blood circulating through a network of blood vessels helps to maintain its temperature, whisking away excess heat.

This is necessary because our brain cells are also extremely heat sensitive. And the function of some of the molecules that pass messages between them are also thought to be temperature dependent, meaning they stop working efficiently if our brains get too hot or too cold.

"We don't fully understand how........

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