Your brain can exceed 40 °C without being ill

23:00. On the thermal map of a healthy brain, the deep regions have already cooled. The night-time drop is part of the daily cycle; looking only at the highest number would erase that information.

16:00. The hottest point in the entire study appears in the thalamus, a deep region that relays sensory signals: 40.9 °C in a healthy woman during the phase after ovulation. The participants’ average brain temperature is 38.5 °C, compared with 36.0 °C measured in the mouth.

09:00. The study recruits forty healthy adults, twenty women and twenty men aged 20 to 40. MRI measurements are scheduled in the morning, the afternoon and late at night. Spectroscopy calculates temperature from chemical signals in the tissue, without putting a probe inside the head.

The study published in Brain in 2022 found average differences of 2.41 °C between regions of the same brain. Deep areas, especially the thalamus, were the hottest; time, age, sex and menstrual cycle all shifted the figure. The full range observed in healthy people was 36.1 to 40.9 °C.