Our brains turn out to be much warmer than expected; in some areas of the brain, the mercury even rises to almost 41 degrees Celsius at certain times!

“For decades, doctors assumed that a healthy brain temperature is constant and equal to body temperature,” researcher Nina Rzechorzek explains. Scientias.nl from. “But several clinical studies have shown that body temperature measurements cannot tell us which temperatures are in the brain. So we also have to measure that brain temperature.” And this is also regularly done for patients who are in the ICU with brain damage. “Our understanding of human brain temperature is mainly based on research among patients with brain damage, where a drill hole in the skull allows fairly accurate measurements of the temperature at a single location in the brain.” However, when interpreting these measurements, doctors systematically run into a problem: they do not know what a normal brain temperature is. “The result is that some patients with brain damage are now being treated to achieve a ‘normal’ brain temperature, while we don’t really know what is really ‘normal’. It is therefore important to find out what a normal brain temperature is and to what extent it can vary among healthy people. This way doctors can determine whether the brain temperature they measure in their patients is abnormal or not and whether treatment is needed.”

MRS

And that is exactly what Rzechorzek and colleagues have now done. They collected 40 healthy subjects and monitored the brain temperature of these subjects for some time. Incidentally, this did not involve a drill; for some time now it has been possible to determine brain temperature using a technique called magnetic resonance spectroscopy, which involves making a scan of the brain. Using this technique, researchers have now determined the temperature of various brain regions of healthy people and have also examined the extent to which that temperature fluctuates over time. And to what extent it also differs from person to person. It leads to some very striking conclusions.

Conclusions

It turns out that the temperature of healthy human brains can rise much higher than previously thought. “We expected this temperature to be higher than body temperature,” says Rzechorzek. But the test subjects still managed to surprise the researchers. “The highest temperature we measured was 40.9 degrees Celsius.” Remarkable, according to researcher John O’Neill. “To me, the discovery that the healthy human brain can reach temperatures that would be diagnosed as fever elsewhere in the body is the most surprising. Such high temperatures have been previously measured in people with brain damage, but were believed to be the result of that brain damage.”

“In the past, it was believed that such temperatures would be harmful to brain cells,” Rzechorzek added. “But none of the scanned people had a high body temperature – they were all healthy and fever-free – and there is no evidence that a temperature of 40.9 degrees Celsius is abnormal for the human brain or that it is directly harmful to human brain cells. ”

fluctuations

“By the way, it’s important to note that only parts of the brain reach such high temperatures. And we’re certainly not suggesting that these areas of the brain are so warm all the time either.” In fact, one of the other striking conclusions is that the brain temperature of people fluctuates quite a bit over time. “The healthy brain temperature changes throughout the day.” It turns out that the temperature of the brain fluctuates by as much as 1 degree Celsius during the day. The highest brain temperatures were measured in the afternoon and the lowest at night.

Women are warmer

For women, it turns out that their brain temperature is influenced by their menstrual cycle. In the period between ovulation and menstruation, their brain temperature is generally 0.4 degrees Celsius higher than in women who are in the first part of their cycle.

Age

“Another surprise was that temperatures were higher in older brains,” Rzechorzek said. Although the age difference between the subjects studied was limited (the oldest was 40 years old and the youngest 20), there was a clear difference in temperature between the youngest and oldest brains. Rzechorzek and colleagues also have ideas on how to explain the warmer brains of older people. “Since blood flow in the brain is very important for the dissipation of heat, we speculate that aging of the blood vessels in the brain affects the main method we humans have at our disposal for cooling our brains. Further research is needed to confirm this, but warming the brain as we age could contribute to age-related conditions, such as dementia.”

brain damage

In addition to studying 40 healthy people, the researchers also looked at previously collected data from 114 people who were hospitalized with brain damage. The temperature of the brains also varied there, the researchers have to conclude. And much stronger than in the healthy test subjects: from 32.6 to 42.3 degrees Celsius. Sufficient data was available from 100 of the 114 patients to determine how the temperature of the brain changed throughout the day. And that also yields interesting insights. For example, the researchers found a correlation between daily variations in brain temperature and the survival chances of the patients. Patients whose brain temperature changed predictably throughout the day were found to be less likely to die than patients whose brain temperature did not change according to a fixed rhythm throughout the day. It raises an interesting question, says Rzechorzek. “Can restoring the daily rhythm in brain temperature increase the survival chances of patients with brain damage?” Follow-up research will have to show that.

Follow-up questions

What we now know, thanks to the 40 healthy test subjects, is that the temperature of the brain is a lot more dynamic and therefore more exciting than expected. That said, however, the research raises even more questions. “What our recent research makes clear is that human brain cells are in an environment with dynamic temperatures; temperatures that change throughout the day. And if that daily rhythm is lost – or less strongly expressed – it could contribute to age-related brain diseases. We have ideas on how that might work and are now testing them. So stay tuned!” But there are more aspects that need further investigation. “While we know quite a bit about how body temperature is regulated (the brain plays an important role in this), we know relatively little about how brain temperature is regulated, so that’s something to look into in the future as well. ” And so there are still more questions to be asked as a result of the research. “How do the variations in normal human brain temperature affect the functioning of the brain cells? How does the brain work under optimal temperatures and what happens when the temperature is not optimal? How does the brain temperature vary in sleep disorders, epilepsy, stroke, brain tumors, dementia, mental illness and inflammation or infections in the brain? And how does the human brain temperature vary during sleep, when people work shifts, age, are pregnant or enter menopause?” Rezechorzek simply lists a few follow-up questions when asked.

Prelude to more

The most recent research into the temperature of our brains is therefore mainly the prelude to more. “The activity of brain cells is temperature dependent,” emphasizes Rezechorzek. “We’ve known that for a long time, and that also applies to other mammal species. In general, brain cells send out signals faster at higher temperatures and slower at lower temperatures. At extreme temperatures, the brain cells stop functioning completely. So there’s an optimal temperature range where the brain cells are at their best, but until we started doing this research, we didn’t know what that temperature range looked like for humans. Now that we know that, we are using the temperatures found in the lab to see how they affect the functioning of the human brain cells we grow there.”

The last word has certainly not yet been said about the temperature of our brains. And further research is extremely important. “We need to change our thinking about human brain temperature,” Rzechorzek says. “Not only for the sake of patients with brain damage, but also to better understand how the brain works, so that we can also better help patients with other brain problems in the future.”