Healthy human brains can be hotter than we thought, reaching nearly 41°C in women, according to a small study.
The findings could change how people with brain injuries are medically managed, says Nina Rzechorzek at the MRC Laboratory of Molecular Biology in Cambridge, UK.
Normal brain temperature is generally assumed to be the same as that of the rest of the body – about 37 °C – yet we had no way to know for sure. People with head injuries sometimes have highly sensitive temperature probes put into their brains, but this isn’t done to people who aren’t undergoing medical treatment.
Rzechorzek’s team looked at the brains of 40 healthy people – half of whom were women – using a technique called magnetic resonance spectroscopy, in which MRI machines measure the temperature of different parts of the brain. This was the first time the technique has been used to measure brain temperature variation over the menstrual cycle. The study didn’t include transgender people.
The brain temperature ranged from 36.1°C to 40.9°C, with the average reading being 2.5°C higher than the body temperature recorded inside the mouth. This makes sense because the brain is highly metabolically active, says Rzechorzek.
The brains of the women in the study were 0.4°C hotter during the second half of the menstrual cycle, between ovulation and menstruation, compared with the first half, and compared with men.
Doctors sometimes try to lower the body temperature of people with brain injuries because they are concerned that high temperatures are harmful, an approach that may need revising, says Rzechorzek. “We [have been] making an assumption
that a value of, for instance, 40°C is abnormal,” she says.
