New research in the journal Brain shows that normal human brain temperature varies much more than previously thought. In healthy people whose oral temperature is usually below 37°C, the average brain temperature is 38.5°C, while deep brain regions often exceed 40°C, especially in women during the daytime. The study suggests that the daily circulation of brain temperature is closely related to survival. These findings could improve the understanding, prognosis and treatment of brain injury.
The new study was led by researchers at the Medical Research Council (MRC) Laboratory of Molecular Biology in Cambridge, UK, who produced the first 4D map of healthy human brain temperature. The graph overturns several previous hypotheses, showing that brain temperature varies with brain region, age, sex and time of day. Importantly, the findings also challenge the commonly held belief that the human brain and body temperature are the same.
To study healthy brains, the researchers recruited 40 volunteers aged 20-40 years and scanned their brains in the morning, afternoon and late at night during the day. They also provided participants with an activity monitor to wear on their wrists so that each person’s biological clock and lifestyle differences could be taken into account. Whether you are a “night owl” or an “early riser”, knowing the biological time of each brain temperature measurement allows you to take into account the differences in each volunteer’s biological clock in your 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 brain temperature varied depending on the time of day, brain region, gender and menstrual cycle, and age.
Although the surface of the brain is usually colder, the temperature of the deeper brain structures tends to be higher than 40°C; the highest brain temperature observed was 40.9°C. In all individuals, brain temperature consistently showed a variation with time of day close to 1°C, with the highest brain temperature in the afternoon and the lowest at night.
On average, women’s brain temperatures were about 0.4°C higher than men’s. This gender difference is likely due to the menstrual cycle, as most women were scanned during the post-ovulatory phase of their cycle, and their brain temperatures were about 0.4°C higher than during the pre-ovulatory phase.
The results also showed that brain temperature rose with age across the range of 20-year differences in participants, most notably in the deeper regions of the brain, which rose by an average of 0.6°C. The researchers suggest that the brain’s ability to cool down may deteriorate with age, and further research is needed to see if this is related to the development of age-related brain disorders.
