New research, published in the journal Brain on the 12th, shows that changes in the temperature of the normal human brain are much greater than previously thought. In healthy individuals whose oral temperatures were typically below 37°C, the average brain temperature was 38.5°C, while deep brain regions frequently exceeded 40°C, especially in women's brains during the day. Research has shown that the daily cycle of brain temperature is closely related to survival. These findings could improve the understanding, prognosis and treatment of brain injury.
The new study, led by researchers at the Medical Research Council (MRC) Molecular Biology Laboratory in Cambridge, UK, produced the first 4D map of the temperature of a healthy human brain. This graph overturns several previous assumptions, showing that brain temperature varies by brain region, age, gender and time of day. Importantly, the findings also challenge a widely held belief that human brains and body temperature are the same.
To study healthy brains, the researchers recruited 40 volunteers between the ages of 20 and 40 to scan their brains in the morning, afternoon and late at night. They also provided participants with an activity monitor to wear on the wrist, so that each individual's biological clock and lifestyle differences could be taken into account. Whether it's a "night owl" or an "early lark," knowing the biological timing of each measurement of brain temperature allows the differences in each volunteer's biological clock to be factored into the analysis.
In healthy subjects, the average brain temperature was 38.5°C, more than 2°C higher than the temperature measured under the tongue. The study also found that changes in brain temperature depend on time of day, brain region, gender and menstrual cycle, and age.
Although the surface of the brain is generally cooler, the deeper structures of the brain tend to be warmer than 40°C; the highest observed brain temperature was 40.9°C. Across all individuals, brain temperature consistently showed a time-of-day variation of nearly 1°C, with the highest brain temperature in the afternoon and the lowest at night.
On average, women's brain temperatures are about 0.4°C higher than men's. This gender difference is likely due to the menstrual cycle, as most women who were scanned during the post-ovulatory phase of their cycle had brain temperatures about 0.4°C higher than the pre-ovulatory phase.
The results also showed that, within the 20-year-old difference of the participants, brain temperature rose with age, most notably in the deep regions of the brain, with an average rise of 0.6°C. The researchers suggest that the brain's ability to cool down may worsen with age, and further research is needed to see if this is involved in the development of age-related brain diseases.
