Epistemic status: Thinking out loud.

Introducing the Question

Scientific puzzle I notice I'm quite confused about: what's going on with the relationship between thinking and the brain's energy consumption?

On one hand, I'd always been told that thinking harder sadly doesn't burn more energy than normal activity. I believed that and had even come up with a plausible story about how evolution optimizes for genetic fitness not intelligence, and introspective access is pretty bad as it is, so it's not that surprising that we can't crank up our brains energy consumption to think harder. This seemed to jive with the notion that our brain's putting way more computational resources towards perceiving and responding to perception than abstract thinking. It also fit well with recent results calling ego depletion into question and into the framework in which mental energy depletion is the result of a neural opportunity cost calculation.

Going even further, studies like this one left me with the impression that experts tended to require less energy to accomplish the same mental tasks as novices. Again, this seemed plausible under the assumption that experts brains developed some sort of specialized modules over the thousands of hours of practice they'd put in.

I still believe that thinking harder doesn't use more energy, but I'm now much less certain about the reasons I'd previously given for this.

Chess Players' Energy Consumption

This recent ESPN (of all places) article about chess players' energy consumption during tournaments has me questioning this story. The two main points of the article are:

  1. Chess players burn a lot of energy during tournaments, potentially on the order of 6000 calories a day (that's about what marathon runners burn in a day). This results from intense mental stress leading to an elevated heart rate and, as a result, increased oxygen consumption. Chess players also tend to eat less during competitions, which also contributes to weight loss during tournaments (apparently Karpov once lost 20 pounds during an extended chess championship).
  2. Chess players and their coaches now understand that humans aren't Cartesian, i.e. our physical health impacts our cognitive performance, and have responded accordingly with intense physical training regimens. On the surface, none of this contradicts the claims I cited above. The article's claiming that chess players burn more energy purely from the side effects of stress, not because their brains are doing more work. So why am I revisiting this question?

Gaps in the Evolutionary Justification

First, reading the chess article led me to notice a big gap in the explanation I gave above for why we shouldn't expect a connection between thinking hard and energy consumption. In my explanation, I mentioned that we should expect our brains to spend much more energy on perceptive and reactive processing than on abstract thinking. This still makes sense to me as a general claim about the median mammal, but now seems less plausible to me as it relates to humans specifically. This recent study, for example, provides evidence that our (humans) big brains are one of two primary causes for our increased energy consumption compared to other primates. As far as I can tell, humans don't seem to have meaningfully better coordination or perceptive abilities than chimps. Chimps have opposable thumbs and big toes, spend their days picking bugs off of each other, and climbing trees. Given this, while I admittedly haven't looked into studies on this but I find it hard to imagine that human brains spend much more energy than chimps on perception.

Let's say that we put aside the question of what exactly human brains use their extra energy for and bucket it into the loose category of "higher mental functions". This still leaves me with a relevant question, why didn't brains evolve to use varying amounts of energy depending on what they were doing? In particular, if we assume that humans are the first and only mammals that spend large fractions of their calories on "extra" brain functions, then why wasn't there selection pressure to have those functions only use energy when they were needed instead of all the time?

Bringing things back to my original point, in my initial story, thinking didn't impact energy consumption because our brains spend most of their energy on other stuff anyway, so there wasn't strong selective pressure to connect thinking intensity to energy consumption. However, I've just given some evidence that "higher brain functions" actually did come with a significant energy cost, so we might expect that those functions' energy consumption would in fact be context-dependent.

Second, it's weird that what we're doing (mentally) can so dramatically impact our energy consumption due to elevated heart rate and other stress-triggered adaptations but has no impact on the energy our brain consumes. To be clear, it makes sense that physical activity and stress would be intimately connected as this connection is presumably very important for balancing the need to eat/escape predators with the need to not use too much energy when sitting around. One doesn't yet make sense to me is that, even though neurons evolved from the same cells as all the rest of our biology, they proved so resistant to optimization for variable energy consumption.

Rescuing the Original Hypothesis

The best explanation I can come up with for the two puzzles I just discussed is that, for whatever reason, evolution didn't select for a neural architecture that could selectively up- and down-regulate its energy consumption depending on the circumstances. For example, maybe the fact that neurons die when they don't have energy is somehow intimately coupled with their architecture such that there's no way to fix it short of something only a goal-directed consequentialist (and therefore not a hill-climbing process) could accomplish. If this is true, even though humans plausibly would've benefited at some point during our evolutionary history from being able to spend more or less energy on thinking, we shouldn't be surprised never happened.

Another weaker (IMO) explanation is that human brains do use more energy in certain situations for some "higher mental functions" but it's not the situations you'd expect. For example, maybe humans use a ton of energy for social cognition and if we could measure the neocortex's energy consumption during parties, we'd find it uses a lot more energy than usual.

1eigen7moThe ESPN article [https://www.espn.com/espn/story/_/id/27593253/why-grandmasters-magnus-carlsen-fabiano-caruana-lose-weight-playing-chess] had a misleading title. They go on to say that a player burns 6000 calories a day , but Caruana [https://en.wikipedia.org/wiki/Fabiano_Caruana] runs an hour a day (or more). These Grandmasters are not reaching into some esoteric mental ability and burning more calories that way; if anyone has ever seen a Grandmaster play against many players at once, or blindfolded (or even blindfolded and against many players!) one can really understand that they see the board in a way that's pretty different from us. The classical theory for this is that they have formed bigger/better chunks than us from excessive playing (the very same way a Mathematician or a Basketball player does). Calorie consumption, is thus correlation in that specific context. Although, I think, a (weak) connection could be made between the use of Language and these chunks formations or using this chunks (who's to say this is not a specialized use of Language?) for the context of a tournament, but I have yet to see anything that support this idea.
1NaiveTortoise7moMy takeaway from the article was that, to your point, their brains weren't using more energy. Rather, the best hypothesis was just that their adrenal hormones remained elevated for many hours of the day, leading to higher metabolism during that period. Running an hour a day is definitely not enough to burn 6000 calories for the record (a marathon burns around 3500). Maybe I wasn't clear, but that's what I meant by the following.

Got it! then I agree with you. I think that a best description of my point would be that yeah, these guys are not burning calories by thinking better or harder. Their exercise plus the higher stress environment could account alone for their high amount burn of calories.

NaiveTortoise's Short Form Feed

by NaiveTortoise 1 min read11th Aug 201885 comments

In light of reading Hazard's Shortform Feed -- which I really enjoy -- based on Raemon's Shortform feed, I'm making my own. There be thoughts here. Hopefully, this will also get me posting more.