HomeScience and ResearchScientific ResearchThere's A Weird Link Between Brain Temperature And Death

There’s A Weird Link Between Brain Temperature And Death

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The first 4D map of healthy human brain temperature created by researchers disproves a number of previously held beliefs and calls into question a long-held belief that the temperature of the human brain and body are the same.

A new study shows that normal human brain temperature fluctuates significantly more than previously believed, and this could be indicative of healthy brain activity. In healthy women and men, the oral temperature is usually less than 37°C, and the average temperature of the brain is 38.5°C. Deeper parts of the brain often get hotter than 40°C, especially during the day for women.

Human brain temperature research has previously depended on data collected from brain-injured patients in intensive care, when direct brain monitoring is frequently required. Researchers have recently been able to quantify brain temperature in healthy people using a brain-scanning technology called magnetic resonance spectroscopy (MRS). However, until today, MRS had not been utilized to investigate how brain temperature varies during the day, or how one’s ‘body clock’ influences this.

The first 4D map of healthy human brain temperature has been created by researchers at the Medical Research Council (MRC) Laboratory for Molecular Biology in Cambridge, UK. This chart disproves a number of previously held beliefs by demonstrating how much brain temperature changes by brain area, age, gender, and time of day. These findings also call into question a long held belief that the temperature of the human brain and body are the same.

Healthy human daily brain temperatures

The study, which was published in the journal Brain, also looked at data from traumatic brain injury patients and found that the presence of daily brain temperature cycles is highly linked to survival. These discoveries could help to improve brain injury diagnosis, prognosis, and treatment.

Differences in brain temperature and health

In order to examine the healthy brain, the researchers selected 40 volunteers aged 20 to 40 years to be scanned at the Edinburgh Imaging Facility, Royal Infirmary of Edinburgh, in the morning, afternoon, and late evening on a single day.

Importantly, they also provided the participants with a wrist-worn activity monitor, which allowed them to account for genetic and lifestyle variances in the timing of each individual’s body clock, or circadian rhythm. Knowing the biological time of day that each brain temperature measurement was collected allowed variances in each volunteer’s body clock to be factored into the study for both ‘night owls’ and ‘morning larks.’

Brain regions included for temperature measurement using magnetic resonance spectroscopy

The average brain temperature in healthy subjects was 38.5°C, more than two degrees higher than the temperature recorded under the tongue. The temperature of the brain fluctuated depending on the following factors, according to the study:

  • Time of day, 
  • brain area, 
  • Gender and menstrual cycle, 
  • and age

While the surface of the brain was normally cooler, deeper brain areas were frequently warmer than 40°C, with the highest temperature recorded at 40.9°C. The brain temperature of all participants varied by roughly 1°C during the day, with the highest temperatures in the afternoon and the lowest values at night.

Female brains were 0.4°C warmer on average than male brains. This gender difference was most likely caused by the menstrual cycle, as the majority of females were scanned during the post-ovulation phase of their cycle, and their brain temperature was around 0.4°C higher than that of females examined during the pre-ovulation period.

The findings also revealed that, during the subjects’ 20-year age span, brain temperature increased with age, most notably in deep brain areas, where the average rise was 0.6°C. According to the researchers, the brain’s ability to cool down may decline with age, and more research is needed to see if this is linked to the development of age-related brain problems.

As explained by Group Leader Dr. John O’Neill:

“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. Such high temperatures have been measured in people with brain injuries in the past, but had been assumed to result from the injury .”

“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 .”

The fluctuations in temperature that occur in injured brains

To investigate the clinical consequences of data gathered from healthy volunteers, researchers analyzed brain temperature data constantly collected from 114 patients with mild to severe traumatic brain injury (TBI). The average brain temperature of the patients was 38.5°C, however, it ranged from 32.6 to 42.3°C.

Only a fourth of the 100 patients with enough data to test for daily rhythms had a daily regularity in brain temperature. When the researchers looked at predictors of survival in intensive care, they discovered that absolute brain temperature measurements were ineffective, but daily brain temperature variation was strongly linked to survival—in fact, only 4% of TBI patients with a daily brain temperature rhythm died in intensive care, compared to 27% of those who did not.

The researchers stress that larger studies are required to validate this connection and that the correlation between brain temperature and survival is merely correlative, meaning that daily brain temperature cycles cannot be presumed to boost survival directly. However, because of the discovered correlation, tracking daily brain temperature cycles in TBI patients could be a potential approach for predicting survival, and more research is needed.

The findings of this study, when combined with data from healthy people, raise critical considerations about the use of therapies in the clinic to modify or manage patient temperature.

The study’s lead author, Dr. Nina Rzechorzek, added:

“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 TBI 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.”

Image Credit: N Rzechorzek/MRC LMB/Brain

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