Scientists create a 4D map of the human brain

By Mark Waghorn via SWNS

A map of the human brain has been created in 4D - showing it is much hotter than the rest of the body.

The organ can be up to 4.5°C warmer - particularly in women during the daytime. It dispels the widely held belief they are the same.

Such fluctuations could be a sign of good health and have implications for the treatment of head injuries - and even Alzheimer's.

Project leader Dr. John O’Neill, of Cambridge University, said: "To me, the most surprising finding is 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 first chart of its kind, named 'HEATWAVE', includes temperature. It was based on 40 healthy volunteers aged 20 to 40 years.

They were scanned at the Royal Infirmary of Edinburgh over one day at three timepoints - 9am, 4pm and 11pm.

Participants were given a wrist-worn activity monitor, accounting for genetic and lifestyle differences in the timing of each person's body clock, or circadian rhythm.

It enabled identification of 'morning larks' or 'night' owls to be factored into the analysis.

Average brain temperature was 38.5°C, more than two degrees than that measured under the tongue.

It also varied depending on time of day, brain region, sex and menstrual cycle and age. The surface was generally cooler.

But deeper brain structures were frequently warmer than 40°C - with the highest observed 40.9°C.

Across all individuals, brain temperature showed consistent time-of-day variation by nearly 1°C, with highest brain observed in the afternoon, and the lowest at night.

On average, the brains of females were around 0.4°C warmer than male counterparts - most likely driven by the menstrual cycle.

Most women were scanned in the post-ovulation phase when temperature was around 0.4°C warmer than that of others.

The results also showed brain temperature went up over the 20-year age range of the participants - most notably in deep brain regions where the average rise was 0.6°C.

The brain's capacity to cool down may deteriorate over time. Further work is needed to investigate if there is a linked with dementia and other age-related brain disorders.

To explore the clinical implications, the researchers then analysed brain temperature data from 114 patients who had suffered moderate to severe head injuries.

The average was 38.5°C. But it varied even more widely - from 32.6 to 42.3°C. Only one-in-four had a daily rhythm in brain temperature.

This was strongly linked with survival. Indeed, of these TBI (traumatic brain injury) patients, only four percent died in intensive care - compared to 27 percent of the rest.

Monitoring daily brain temperature cycles has potential as a tool for predicting prognosis, say the British team.

The overall findings also raise important questions about the use of interventions to modify or control patient temperature in the clinic.

Study leader Dr Nina Rzechorzek, also from Cambridge, said: "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 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."

Previously, such studies have relied upon data capture from brain-injured patients in intensive care, where direct monitoring is often needed.

More recently, a brain scanning technique called MRS (magnetic resonance spectroscopy), has enabled non-invasive measurements in healthy people.

But it had not been used to explore how brain temperature varies throughout the day or to consider how an individual's 'body clock' influences this - until now.

The study in Brain was funded by the Medical Research Council.