Rather tickled to discover that contrary to the belief of some ancient greeks, it seems that the brain isn’t an organ for cooling the blood:
Increasing [cerebral blood flow] in a specific deep brain region can cause a resultant decrease in brain temperature there. According to the author mammal’s brains can sustain a temperature upwards of 42 Celsius without becoming damaged. Though, the optimum temperature may be much lower than that. Certain drugs have the ability to increase the brain’s temperature in part by vasoconstriction. Cerebral blood flow only acts as a coolant inside deeper brain regions where the blood is cooler than the surrounding brain tissue. So it’s really not a coolant in the same manner as that in a heat engine. The cbf actually heats up more superficial brain regions that are closer to the skull so the mechanism is not uniform. The main purpose of cerebral blood flow is to bring glucose to neurons for their basic energy need. So the cooling ability is sort of a secondary aspect of blood flow and is probably not ideally suited for that purpose. Evolution has basically co-opted one process for a different purpose entirely. The blood flow’s ability to cool is more important for larger brained mammals and less relevant for smaller brained ones where heat can dissipate from the head easier.
This comes in the context of a paper that applies thermodynamics to answer the question of how big (and powerful) brains can potentially get.
Click here for the answer… [Brainstimulant blog]