The human brain is probably much hotter than previously thought – temperatures can reach over 40°C.
Scientists say that brain temperature can fluctuate more throughout the day than anyone could have imagined.
The new study has been published in the journal Brain.
While the human body typically has a temperature of around 37°C (98.6°F), it appears that the temperature of the brain varies. A healthy brain is hotter than previously thought and could be more than 2°C (3.6°F) warmer than the rest of our bodies, according to a new study.
Healthy study participants had an average brain temperature of 38.5°C (101.3°F ), which is as much as 2.5°C (4.5°F) higher than the average oral temperature. In the deeper regions of the brain, temperatures often exceeded 40°C (104°F), with 40.9°C (105.6°F) being the highest temperature recorded.
The study found that brain temperature is not fixed—it varies more than scientists once thought, depending on age, gender, menstrual cycle, brain region, and time of day.
“To me, the most surprising finding of our study is that the brain of a healthy person can reach a temperature that would be diagnosed as a fever in any other part of the body. Such high temperatures have been measured in people with traumatic brain injuries in the past, but were thought to be the result of trauma,” said Dr. John O'Neill, team leader in the Medical Research Council's Molecular Biology Laboratory, in a statement.
“Normal” brain temperature in humans has never been determined. Instead, it is usually assumed to be the same as the rest of the body. Previous studies used data from brain-injured patients whose brains were directly observed. Brain temperature can now be measured in healthy individuals using magnetic resonance spectroscopy (MRS), a non-invasive brain scanning technique.
Using MRS, the new study team studied the brains of 40 healthy people – 20 men and 20 women – aged 20 to 40. The measurements were taken three times during the day, making it the first time MRS has been used to track changes in brain temperature throughout the day.
Brain temperature ranged from 36.1°C to 40.9°C (97°F to 105.6°F). The surface of the brain tended to be colder, while the deeper regions were significantly warmer. For example, the thalamus, one of the deepest parts of the brain, recorded the highest temperature.
It has also been found that a person's gender affects their brain temperature. Women's brains were 0.36°C (0.65°F) warmer in the second half of their menstrual cycle after ovulation than in the first half or compared to men's brains.
All participants were found to have brain temperature fluctuated up to 1°C (1.8°F) during the day. Brains were hottest during the day and coldest at night.
“We found that brain temperature drops at night before bedtime and rises during the day. There is good reason to believe that these daily fluctuations are associated with long-term brain health—something we hope to explore further,” added O'Neill.
The authors caution that their results so far are purely correlational and needing confirmation in larger studies, they remain optimistic that they may be of clinical value in the treatment of traumatic brain injury.