Is it normal to have a hot head? Unexpectedly, a healthy brain temperature can reach 40℃ everyday!

When people are excited, they do some irrational things, which is often said to be "hot-headed". However, scientists have recently found through measuring "brain temperature" that the brain of a healthy person is actually hotter than we thought in the past. Compared with normal body temperature, the brain is indeed often in a "hot" state.

Image source: 123RF

Compared with measuring body temperature, measuring "brain temperature" is obviously much more difficult. After all, it is unlikely that we can insert a thermometer into the brain under normal circumstances. There are exceptions. Occasionally, in cases of severe head injuries, for the purpose of treatment, doctors will put a highly sensitive probe into the patient's brain to directly monitor temperature changes. However, the brain temperature measured in this case cannot represent the brain of a healthy person.

Now, with the help of a magnetic resonance imaging (MRI) scanner, researchers at the MRC Laboratory of Molecular Biology in Cambridge, UK, have used a technique called magnetic resonance spectroscopy to non-invasively measure the temperature of multiple parts of the brain of healthy adults. By taking multiple consecutive measurements, they have determined the range of variation in human brain temperature.

▲The research results were recently published in the professional academic journal Brain

The study found that the normal temperature of the human brain is between 36.1°C and 40.9°C, with an average brain temperature of 38.5°C. Compared with the body temperature read by mouth (average 36°C), the brain temperature is 2.5°C higher, clearly showing the truth of "brain burning".

As for why the brain temperature is so high, the researchers believe it is not difficult to understand. After all, we know that the brain is an organ with high metabolic activity.

Not only is the brain warmer than previously thought, but it also varies more than researchers expected, with changes related to sex, age, brain region, the circadian clock (time of day), and women's menstrual cycle.

▲This study constructed a 4D map showing changes in brain temperature for healthy adults (Image source: Reference [1])

The researchers compared the brain temperatures of 20 men and 20 women and found that women's brains were, on average, slightly hotter, about 0.4°C hotter than men's brains. This gender difference is likely related to the menstrual cycle, because most women's brain temperatures are nearly 0.4°C higher in the second half of their menstrual cycle, the luteal phase after ovulation, than in the first half.

The temperature of the brain also fluctuates at different times of the day. The researchers took measurements in the morning, afternoon and evening and found that the brain temperature varied by nearly 1°C in a day: it cooled down at night and rose during the day, with the highest temperature observed in the afternoon. The researchers explained that this may be because when we sleep, more blood flows to the brain, helping it cool down. This may also remind us again of the importance of sleep: to avoid long-term overheating of the CPU.

The results also showed that among the participants aged 20 to 40, the older they were, the hotter their brains became, increasing by 0.6°C in 20 years. The most significant temperature change was in the thalamus, which is located deep in the brain and is also a relatively high temperature area in the entire brain.

The researchers suggest that the brain's ability to cool itself may weaken with age, and it's worth examining whether this change is linked to older people's susceptibility to brain disease.

▲The researchers selected 80 areas in the brain for measurement, including the hypothalamus (Hypo) and thalamus (Thal) located deep in the brain (Image source: Reference [1])

These new findings about brain temperature could change the way people with brain injuries are treated and cared for.

In this paper, the researchers also analyzed more than 100 patients with moderate to severe traumatic brain injury (TBI) and compared their brain temperature data. It was found that the average brain temperature of these patients was similar to that of healthy people, but the temperature range was larger. "Doctors sometimes try to lower the temperature of patients with brain injuries because they are worried that high temperatures may be harmful. This approach may need to be modified." said Dr. Nina Rzechorzek, the leader of the study.

A more significant difference is the daily rhythmic changes in brain temperature - only 1/4 of the patients have daily rhythmic changes. This rhythmic change is also closely related to the patient's survival rate: up to 27% of patients with traumatic brain injury who lack rhythmic changes in brain temperature will die during intensive care, compared with 4% of patients who still have rhythmic changes in brain temperature during intensive care.

"These data suggest that measuring brain temperature around the clock could have great clinical value," Dr. Rzechorzek added. "Our work also opens the door to future studies into whether disruptions in the daily rhythm of brain temperature could serve as an early biomarker in several age-related brain diseases, such as dementia."

References:

[1] Nina M. Rzechorzek et al., (2022) A daily temperature rhythm in the human brain predicts survival after brain injury. Brain. Doi: https://doi.org/10.1093/brain/awab466

[2] Healthy human brains are hotter than previously thought, exceeding 40 degrees. Retrieved June. 14, 2022 from https://www.eurekalert.org/news-releases/955387