Hotter human brains are actually healthy and protective

June 14, 2022
Hotter human brains are actually healthy and protective

Healthy brain function is indicated by warmer human brain temperatures, and varies depending on the time of day, brain region, sex and menstrual cycle, and age, according to researchers from the UK. In healthy participants of a study at the Edinburgh Imaging Facility, Royal Infirmary of Edinburgh, the average brain temperature was found to be more than two degrees warmer than that measured under the tongue, at 38.5°C.

“To me, the most surprising finding from our study is that the healthy human brain can reach temperatures that would be diagnosed as fever anywhere else in the body,” said Dr. John O’Neill, Group Leader at the Medical Research Council (MRC) Laboratory for Molecular Biology. “Such high temperatures have been measured in people with brain injuries in the past, but had been assumed to result from the injury.”

The human brain surface is generally cooler, while deeper brain structures can be warmer than 40°C; with the highest observed brain temperature being 40.9°C. A brain temperature study by MRC researchers, across 40 participants – taking into account the genetic and lifestyle differences in the timing of each participant’s body clock – showed consistent time-of-day variation by nearly 1°C, with highest brain temperatures observed in the afternoon, and the lowest at night.

“We found that brain temperature drops at night before you go to sleep and rises during the day. There is good reason to believe this daily variation is associated with long-term brain health – something we hope to investigate next,” said Dr. O’Neill.

In the same study, on average, female brains were found to be around 0.4°C warmer than male brains – this sex difference was driven by the menstrual cycle, since most females were scanned in the post-ovulation phase of their cycle (the brain temperature was slightly lower in females scanned in their pre-ovulation phase).

The results also showed that brain temperature increased with age, most notably in deep brain regions, where the average increase was 0.6°C. This led researchers to propose that the brain’s capacity to cool down may deteriorate with age.

Using a novel technique called magnetic resonance spectroscopy (MRS), MRC researchers have also produced the first detailed 4D map of healthy human brain temperature – challenging previous assumptions that the human brain and body temperature are the same.

Dr. Nina Rzechorzek, MRC Clinician Scientist Fellow, commented: “Using the most comprehensive exploration to date of normal human brain temperature, we’ve established ‘HEATWAVE’ – a 4D temperature map of the brain. This map provides an urgently needed reference resource against which patient data can be compared, and could transform our understanding of how the brain works. That a daily brain temperature rhythm correlates so strongly with survival after [traumatic brain injury] suggests that round-the-clock brain temperature measurement holds great clinical value.

“Our work also opens a door for future research into whether disruption of daily brain temperature rhythms can be used as an early biomarker for several chronic brain disorders, including dementia.”

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Hotter human brains are actually healthy and protective

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