Kind of a nitpick, but if radiative heat loss has almost nothing to do with how chips are cooled, and it has almost nothing to do with how the brain is cooled, then why are we even bringing up the Stefan-Boltzmann law in the first place?
I think a keyword here (if you want to google on your own) is “selective brain cooling (SBC)”. In practice this might be on a continuum, but this might be an area where humans have some unique adaptations?
The basic mechanisms tend to involve things like a “plexus” of veins/arteries for heat exchange, dynamic blood routing based on activity, and then trying to set up radiators somehow/somewhere on the body to take hot blood and push the heat into the larger world. Many mammals just have evaporative cooling in their mouth that runs on saliva, but humans (and maybe pigs) have it over their whole body. Elephant ears seem like another non-trivial adaptation related to heat. One possibility is that the cetaceans are so smart (as an evolutionary branch) because they have such a trivially easy way to get a water cooled brain.
I’ve looked into this enough to buy a tool for short/quick experiments in specialized brain cooling, but they have been very low key. No blinded controls (obviously) and not even any data collection. Mostly I find the cap to be subjectively useful after a long phone call holding a microwave transmitter next to my head, where I feel a bit fuzzy brained after the call… then the cap fixes that pretty fast :-)
In practice I think water cooled super performance (in this case the paradigmatic performance test is pull-ups) does seem to be a thing though I know of no cognitive version at this time. I’ve never thought in a highly focused way about exactly this topic.
If heat dissipation is a real bottleneck on mental performance then my vague priors suggest: (1) it would mostly be a bottleneck on “endurance of vigorous activity” like solving logic puzzles very fast for hours at a time, and (2) IF heat was the bottleneck and that bottleneck was removed THEN whatever the next bottleneck was (like maybe neurotransmitter shortages?) it might have much worse side effects when it hits (seizures? death?) because whatever the failure mode is, it probably has been optimized by evolution to a lesser extent.
Fascinating! I’m going to link this in to the main article. I was aware of the whole “humans adapted to long distance running” thing, and how sweat is optimized for that, but I hadn’t considered the related implications for brain cooling.
Human brains are about 3x larger, and thus require/output 3x more energy and surface power density, than our similar-ish sized primate relative with similar-ish sized skulls. Brain tissue also has a 10x higher power density than the rest of the body. This does suggest the need for significant evolutionary optimization towards cooling.
There is a minor literature on the evolution of brain cooling as potentially “blocked in early primates and then unblocked sorta-by-accident which allowed selection for brain size in hominids as a happy side effect”. I’m unsure whether the hypothesis is true or not, but people have thought about it with some care and I’ve not yet heard of anyone figuring out a clean kill shot for the idea.
I’m just thinking—it might be that while heat does determine brain efficiency to a large degree it might not be so simple as it might be determined by the architecture.
DIfferent animals might be adapated to a certain temperature range—it might not make your brain more efficient when it is cooled in this way.
does anybody know how the cognition of coldblood creatures varies as they warm and cool throughout the day?
I’m not sure what theory that observation would test cleanly, since ectotherms have such a complicated relationship to heat.
One thing I just checked is honeybees, which I’ve read a book or two about, because I know they have large cooling requirements for their wing muscles (their blood doesn’t move O2, it just moves heat, basically). When the hive gets cold in the winter, some go to the center and lock their wings with their arms, and shiver their wing muscles, and this heats the entire hive. So they are kind of endothermic? Maybe? Depending on definitions?
It looks like probably individual honeybee brains are cooled by using honey sort of like how dogs use saliva, with evaporative cooling from the mouth. Then, when flying on a very hot day, the waste heat from the wings is moved, by the blood, to the thorax (but not to the head) to use the thorax as a radiator.
When it is cold, the stationary wings can send heat to the thorax via the blood, but somehow the head doesn’t need this.
SB law describes the relationship to power density of a surface and corresponding temperature; it just gives you an idea of the equivalent temperature sans active cooling. For the brain that temperature is just similar to a dark surface receiving constant sunlight, so it’s not a serious cooling challenge.
That section was admittedly cut a little short, if I had more time/length it would justify a deeper dive into the physics of cooling and how much of a constraint that could be on the brain. You’re right though that the surface power density already describes what matters for cooling.
Kind of a nitpick, but if radiative heat loss has almost nothing to do with how chips are cooled, and it has almost nothing to do with how the brain is cooled, then why are we even bringing up the Stefan-Boltzmann law in the first place?
I think a keyword here (if you want to google on your own) is “selective brain cooling (SBC)”. In practice this might be on a continuum, but this might be an area where humans have some unique adaptations?
The basic mechanisms tend to involve things like a “plexus” of veins/arteries for heat exchange, dynamic blood routing based on activity, and then trying to set up radiators somehow/somewhere on the body to take hot blood and push the heat into the larger world. Many mammals just have evaporative cooling in their mouth that runs on saliva, but humans (and maybe pigs) have it over their whole body. Elephant ears seem like another non-trivial adaptation related to heat. One possibility is that the cetaceans are so smart (as an evolutionary branch) because they have such a trivially easy way to get a water cooled brain.
I’ve looked into this enough to buy a tool for short/quick experiments in specialized brain cooling, but they have been very low key. No blinded controls (obviously) and not even any data collection. Mostly I find the cap to be subjectively useful after a long phone call holding a microwave transmitter next to my head, where I feel a bit fuzzy brained after the call… then the cap fixes that pretty fast :-)
In practice I think water cooled super performance (in this case the paradigmatic performance test is pull-ups) does seem to be a thing though I know of no cognitive version at this time. I’ve never thought in a highly focused way about exactly this topic.
If heat dissipation is a real bottleneck on mental performance then my vague priors suggest: (1) it would mostly be a bottleneck on “endurance of vigorous activity” like solving logic puzzles very fast for hours at a time, and (2) IF heat was the bottleneck and that bottleneck was removed THEN whatever the next bottleneck was (like maybe neurotransmitter shortages?) it might have much worse side effects when it hits (seizures? death?) because whatever the failure mode is, it probably has been optimized by evolution to a lesser extent.
Fascinating! I’m going to link this in to the main article. I was aware of the whole “humans adapted to long distance running” thing, and how sweat is optimized for that, but I hadn’t considered the related implications for brain cooling.
Human brains are about 3x larger, and thus require/output 3x more energy and surface power density, than our similar-ish sized primate relative with similar-ish sized skulls. Brain tissue also has a 10x higher power density than the rest of the body. This does suggest the need for significant evolutionary optimization towards cooling.
There is a minor literature on the evolution of brain cooling as potentially “blocked in early primates and then unblocked sorta-by-accident which allowed selection for brain size in hominids as a happy side effect”. I’m unsure whether the hypothesis is true or not, but people have thought about it with some care and I’ve not yet heard of anyone figuring out a clean kill shot for the idea.
Woah Jennifer this is wild stuff. Fascinating!
I’m just thinking—it might be that while heat does determine brain efficiency to a large degree it might not be so simple as it might be determined by the architecture.
DIfferent animals might be adapated to a certain temperature range—it might not make your brain more efficient when it is cooled in this way.
does anybody know how the cognition of coldblood creatures varies as they warm and cool throughout the day?
I’m not sure what theory that observation would test cleanly, since ectotherms have such a complicated relationship to heat.
One thing I just checked is honeybees, which I’ve read a book or two about, because I know they have large cooling requirements for their wing muscles (their blood doesn’t move O2, it just moves heat, basically). When the hive gets cold in the winter, some go to the center and lock their wings with their arms, and shiver their wing muscles, and this heats the entire hive. So they are kind of endothermic? Maybe? Depending on definitions?
It looks like probably individual honeybee brains are cooled by using honey sort of like how dogs use saliva, with evaporative cooling from the mouth. Then, when flying on a very hot day, the waste heat from the wings is moved, by the blood, to the thorax (but not to the head) to use the thorax as a radiator.
When it is cold, the stationary wings can send heat to the thorax via the blood, but somehow the head doesn’t need this.
What do you think this might imply for the brain & cognition?
SB law describes the relationship to power density of a surface and corresponding temperature; it just gives you an idea of the equivalent temperature sans active cooling. For the brain that temperature is just similar to a dark surface receiving constant sunlight, so it’s not a serious cooling challenge.
That section was admittedly cut a little short, if I had more time/length it would justify a deeper dive into the physics of cooling and how much of a constraint that could be on the brain. You’re right though that the surface power density already describes what matters for cooling.