Post-Activation Brain Warming: A 1-H MRS Thermometry Study

PURPOSE: Temperature plays a fundamental role for the proper functioning of the brain. However, there are only fragmentary data on brain temperature (T(br)) and its regulation under different physiological conditions. METHODS: We studied T(br) in the visual cortex of 20 normal subjects serially with a wide temporal window under different states including rest, activation and recovery by a visual stimulation-Magnetic Resonance Spectroscopy Thermometry combined approach. We also studied T(br) in a control region, the centrum semiovale, under the same conditions. RESULTS: Visual cortex mean baseline T(br) was higher than mean body temperature (37.38 vs 36.60, P<0.001). During activation T(br) remained unchanged at first and then showed a small decrease (-0.20 C°) around the baseline value. After the end of activation T(br) increased consistently (+0.60 C°) and then returned to baseline values after some minutes. Centrum semiovale T(br) remained unchanged through rest, visual stimulation and recovery. CONCLUSION: These findings have several implications, among them that neuronal firing itself is not a major source of heat release in the brain and that there is an aftermath of brain activation that lasts minutes before returning to baseline conditions.