Heat does not melt the brain, but it is capable of denaturing the proteins that make up our cells. From 40ºC, the organ can begin to lose its adjustment in several planes: confusion, relegating functions or uncoordinated movements.
With high temperatures, this crucial organ can be somewhat confused by lack of habit. One of its parts, the hypothalamus -hyperexhausted to regulate the heat of the whole body- leaves many of its functions in the background, and some neurons, such as those that coordinate movements, become affected.
Heat also alters the transmission of nerve impulses and makes them go much slower. Hence, we can be a bit dazed, more listless and without much desire to work or do leisure activities with the sun still on. And that's not all, when heat affects the blood-brain barrier (a network that protects the brain from harmful substances), coupled with dehydration, you can experience minor memory loss.
The first thing that happens to the brain when it experiences a lot of heat on a continuous basis is confusion. “Our brain, depending on light intensity, for example, prepares us to be awake or asleep. The same goes for temperature. When there are prolonged high temperatures, he does not understand that information and gets confused”, explains José A. Morales-García, professor and scientific researcher in Neuroscience at the Complutense University of Madrid.
Heat also has consequences on the hypothalamus, which is the region of the brain responsible for regulating a large number of functions, including maintaining a constant temperature, the release of hormones, sleep or even moods. “All this influences the character. We are more dazed and have loss of attention.”
When the hypothalamus focuses almost exclusively on controlling heat so that it does not affect the body or the brain, it leaves the rest of its functions in the background. Hence, it can be difficult to sleep or a person feels apathetic in the middle of a heat wave like the one that has hit Spain this July. "All this greatly affects the nervous system," adds the specialist.
The hypothalamus regulates body temperature through vasodilation and vasoconstriction. In the first, the blood vessels widen, get closer to the skin and favor heat loss through sweat. In the second, the vessels shrink, move away from the skin and prevent heat loss. “In summer we sweat and in winter we get chills. A shiver is neither more nor less than opposing movements of the muscles to produce energy so that we are not cold”, describes Morales-García.
However, a critical point may come for the hypothalamus. “If the temperature starts to get too high, the hypothalamus goes crazy because all its effort is to keep your temperature constant and it doesn't always succeed. That's when you can get a heat stroke ". Heat strokes affect children, the elderly and people with previous pathologies more.
“Another thing that happens when the temperature rises a lot is that the transmission of the nerve impulse is much slower. Neurons communicate through nerve impulses. The heat makes us more dazed, inattentive, listless and slower when reacting to any stimulus”, says the neuroscientist.
The brain does not melt from heat, as is popularly said on many occasions. But proteins do come out very badly. “Heat causes proteins to denature. This affects the cells and some cells of the nervous system are affected more than others. For example, in the neurons of the cerebellum, the Purkinje neurons –which are responsible for coordinating movement– are especially sensitive”, says the researcher. When this happens, "the proteins begin to die and, when they die, they begin to generate a series of cellular debris that produce inflammation."
On the other hand, heat can also affect the blood-brain barrier, which is the one that surrounds the brain, and, together with dehydration, can cause changes in the hippocampus, an area that is related to memory, and thus produce small losses of regards.
When the body is not able to reduce the temperature, it is when heat stroke can arrive, the consequences of which range from a lack of coordination to the death of neurons. People who die, the expert points out, usually present "a cardiovascular disorder" and, in most cases, it is due to previous pathologies. "In the case of older people, as a consequence of age, temperature regulation is not as effective as that of a younger person."
For the neuroscientist, "you have to be very careful" with the idea that some people tolerate heat better than others when going out to play sports. “When you run you need a very high energy input and you generate a lot of heat. If you generate a lot of heat and on top of that the environment that surrounds you is very hot, you have all the ballots for it to give you a heat stroke”.
The prick some people feel near the forehead when drinking a very cold drink in hot weather is actually a wake-up call from the nervous system. “By having a very cold drink, what you are telling your cardiovascular system, and then your brain, is that it is cold. And if it's cold we have to keep the temperature down”, explains Morales-García. But that ice cream or that drink with a lot of ice is really something momentary. Is it cold or is it hot? This is what the cardiovascular system asks itself.
“All this information is sent to the nervous system and it gives us a touch, it calls our attention. And the way he gets our attention is through pain.” The sting is felt in the forehead because the pain receptors are in the mouth and throat. However, not everyone experiences this when they drink a cold drink. It depends on the nerve that sends this information to the brain, which is the trigeminal nerve. “In some people it is much more sensitive than in others. That is why in those who have it more sensitive they can feel this pain. There are studies that correlate pain when drinking cold drinks with also being more predisposed to suffer from migraines, ”he concludes.