What’s the average brain temperature?
I once asked that query to a young buck neurosurgeon while we’re both side by side at the Cafe Neuro (Montreal Neurological Institute) lunch counter. He glanced sideways with that bored look in his eyes, “What do you mean, average?” as he leered at me. “Well I bet in a long procedure you literally have your fingers in brain tissue, did you ever measure the temperature during the operation?” I know I surprised him, I could see the quick cloud race across his eyes. “I mean anaesthesia is known to drop the body temperature does it drop the brain temperature, in your experience?” as I probed hard wood with him. “Well as the procedure gets on the long, we do take measures to keep the patient cool but not too cool,” he cooed, clearly bored with the idiot beside him at the lunch counter. “Have you read Mellergard’s observations of brain temperature?” I was skating back, behind the net, now reacting to his arrogance with me.“Who’s Mellergard?” he shot back. ” Mellergard is a Swedish neurosurgeon who has reported a measurable temperature difference between core/central brain areas versus cortex, Mellergard calls it a thermal gradient,” now I saw his flustered anger rising in his eyes. ” My tuna sandwich is here, I gotta go back to the OR,” he abruptly huffed, as he swept his gown at me, stepping away as if on a movie shoot from the lunch counter. I thought to myself, “You should have read Mellergard’s article, it’s only a critical part of your business.”
When I first came across Mellergard’s observations I was stunned by his evidence. After much reading in the medical literature, there was a lot of shivering threshold observations from researcher Sessler, what he termed an intra threshold difference of brain temperature. In my own simple observations measuring brain temperature in Hanna Pappius lab, I had caught something unusual one day. For our edema experiments, that I mentioned in an earlier Post, they were in fact concussion damage experiments. My expertise was to make a surgical opening in the rat’s skull then place a gadget we had custom-made for freezing a small 5mm circle of the exposed brain tissue. I had a rectal thermometer inserted into my animal. Then I did one of those serendipity things. I had a Cole-Palmer thermister with a very fine tip that I suddenly inserted into the rat’s huge masseter muscle. The masseter muscle is fed from a branch of the internal carotid, it’s the big muscle on the side of their skull that gives them such strong biting strength. I was inducing the animal with 2.5 % halogen anesthetic gas, to put the animal to sleep for the surgery. I glanced at the rectal temperature, getting 37 degrees centigrade. Then I must have looked confused at the thermister temperature reading from the masseter muscle, the temperature was falling. I tapped the instrument, was it working right I wondered to myself. I got out my notebook to kept track of the thermite temperature in 10ths of a degree centigrade. I made my usual lesion (concussion mimic) damage on the brain with our minus 50 centigrade cooling device held gently in contact with the cortex for 5 seconds. Over the next few weeks I kept track of the masseter temperature changes with the anesthetic induction each time I did an experiment. We treated our edema/concussed animals with a variety of drugs that Dr Pappius was employing, attempting to reduce the brian damage I was giving to our animals. Something was wrong. Our controls weren’t working. Even though I was making real brain damage something was making the damage resolve. After much debate among ourselves we were questioning everything in my technique. Research is like this. Things can go haywire without an easy answer of what is going off, especially in brain protocols. Then I mentioned to Dr Pappius about my masseter temperature measurements. We said it together, “The brain is being cooled under the influence of the halothane !” Hence no damage shows up since the cooled brain is being protected by the drop in brain temperature. The anesthesia researcher Sessler, termed this effect as disturbing the shivering threshold set temperature. But what about Mellergard’s thermal temperature gradient that he was measuring within human brains?
What’s going on here, in terms of brain temperature? Is brain temperature different to body temperature? As my very skilled research supervisor Dr Sandra Miller alway says, ‘ ask what is the advantage for Nature to do this?’ That is not easy, I don’t have a ready answer for that question. The brain temperature cycles 2 degrees Centigrade about 3 cycles per hour, perhaps if I were to stretch the interpretation, purge the short term memory that needs not be saved? That’s just a guess. I don’t know why, more research. But brain temperature is under its own dedicated network that is similar to body, core temperature but a different network. More work is needed there to resolve the Mellergard gradient thing.
Here’s my conclusion about brain temperature : I have made up my own definition for brain temperature, I call it brainsett. We have all been taught that our brain’s have a built in thermostat, correct? Not quite- it looks like Nature has two set points for keeping the brain temperature regulated. We have to satisfy what Mellergard has actually measured. He has measured people’s brain temperature the moment they show up at his hospital with horrible head injuries, literally with portions of their brain exposed in open wounds, horrific injuries. He would measure inside to the exposed central portion as well as at the outer surface recording his temperature measurements. He always observed a thermal gradient within these trauma brains, hotter at the brain core, cooler toward the outside in the cortex areas. To control such a difference of temperature at the same time suggest strongly that the thermister set point is not one set point, it would involve two set points. That is why I call my brain temperature brainsett, with two t’s, one for each set point. A lower limit plus an upper limit, that cycles 3 times per hour, varying approximately 2 degrees centigrade each cycle.
Now let’s go back to my early observations making rat concussions for Dr. Pappius. As the masseter muscle, which is fed by the internal carotid feeds the muscle, the muscle also mimics temperature wise what is happening with the other internal carotid feeding inside the brain. The halogen anaesthesia is affecting the lower set point, hence there will be a drop in brain set temperature. But the animal has a higher set point too. What’s happening here? If a fever were to start at the induction of the anesthesia there would be a crisis of temperature set point activity. The brain temperature would rise. What happens when people with brain injuries have fever? They do very poorly, usually they don’t make it through a bad crisis. If you have a stroke plus a fever, this is very bad news. My opinion is get that brain temperature down as first priority.
I’m running through this brain temperature material very fast for the reader. What does it have to do with the theme of concussions or other minor head trauma? To save the brain influence the lower set point get the brain cooler, that is what should be done. The Hopital Ste-Justine des Enfants here in Montreal tries to accomplish this kind of intervention. It is extremely difficult. You require dedicated nursing staff who are super diligent to keep a young patient’s body cool to keep a brain cool. The extra work is worth it, in terms of recovery from the damage. Does any trainer think about cooling the brain after a concussion? No- the knowledge is simply not out there in the public domain. That’s my job to get that sort of good information out there to start protecting a damaged concussed brain right away. Race drivers understand this already. In NASCAR, there is a special cooling unit inside the helmet surrounding the drivers head. The inside car temperature can reach easily to 150 degrees fahrenheit. A driver to perform inside such an oven without helmet/brain cooling would fade totally during the course of a three hour race.
Why not cooling helmets for primary concussion treatment? The technology is already out there, in place. Just ask Jacques Villeneuve, he uses a cooling helmet.