It’s pretty warm in a healthy brain. The mean brain temperature of 38.5 degrees Celsius is more than two degrees higher than a measurement in the mouth, as a British research group has now reported in the journal Brain. In the deeper brain regions, it often even exceeds 40 degrees – a value that would be diagnosed as fever elsewhere in the body.
The team led by Nina Rzechorzek from the MRC Laboratory for Molecular Biology in Cambridge recruited 40 healthy volunteers between the ages of 20 and 40 and measured their temperatures in different brain regions in the morning, afternoon and evening using magnetic resonance spectroscopy (MRS). In all test subjects, the brain temperature fluctuated by almost 1 degree Celsius over the course of the day. In the evening it fell, during the day it rose again. The highest values were measured in the afternoon. A woman set the record: 40.9 degrees Celsius in the thalamus – the brain region where it was warmest on average.
On average, the women’s brain temperatures were around 0.4 degrees Celsius higher than those of men. The researchers suspect that this probably has something to do with the menstrual cycle: After ovulation, the temperatures are higher, and most women were in this phase when the measurement was taken. Temperature also increased with age, especially in the deeper brain regions.
From this data, the researchers created what they say is the first 4-D map of brain temperature – “an urgently needed reference source,” says study leader Nina Rzechorzek. They compared readings from more than 100 intensive care patients with craniocerebral trauma: the average brain temperature was one degree lower. In addition, it fluctuated between 32.6 and 42.3 degrees Celsius and thus more than in the healthy volunteers (36.1 to 40.9). But only a quarter of the sick showed the typical daily rhythm of healthy people. If the rhythm was missing, the risk of death increased by a factor of 20.