A small but revealing study suggests that even mildly stressful intellectual challenges change our emotional states and behaviors, even if they do not profoundly alter brain metabolism. Fourteen female Canadian college students either sat around, summarized a passage of text or completed a series of computerized attention and memory tests for 45 minutes before feasting on a buffet lunch. Students who exercised their brains helped themselves to around 200 more calories than students who relaxed. Their blood glucose levels also fluctuated more than those of students who just sat there, but not in any consistent way. Levels of the stress hormone cortisol, however, were significantly higher in students whose brains were busy, as were their heart rates, blood pressure and self-reported anxiety. In all likelihood, these students did not eat more because their haggard brains desperately needed more fuel; rather, they were stress eating.
Messier has related explanation for everyday mental weariness: "My general hypothesis is that the brain is a lazy bum," he says. "The brain has a hard time staying focused on just one thing for too long. It's possible that sustained concentration creates some changes in the brain that promote avoidance of that state. It could be like a timer that says, 'Okay you're done now.' Maybe the brain just doesn't like to work so hard for so long."
*Editor's note: The last two sentences of the seventh paragraph were edited after publication for clarity and accuracy
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Add CommentFantastic article! I really appreciate the extra effort taken by the author, especially the math converting resting metabolic rate to a measure of power. Editor please promote this guy.
Reply | Report Abuse | Link to thisThose of you who frequent articles on this website should know what I mean: how many times have you clicked on an interesting article title only to find 2 or 3 paragraphs of dribble and fluff? (Complete with typos, misquotes, inaccuracies, lack of basic science, faulty hypothesis, etc. - many other writers for this website lack basic math and science knowledge, and in fact, can just barely string together a small story putting to question their training as a English and/or technical writer).
Thanks for the article. I have often wondered about how much energy it takes to think. Sometimes, when working on a complex machine design for months on end, I have to eat twice as much.
Reply | Report Abuse | Link to thisI also wonder, do heavy thinkers typically have a higher body temperature? What is the typical range of body temperatures for people?
Thanks,
-Tony
One assumption made by most when first learning about neuroscience is that a neuron fires, kind of like a circuit getting a charge, and that firing is what processes the information. More firing neurons equals more thinking, which equals more energy consumption. Well this is entirely wrong. Only some of the time does it work this way. However quite often a neuron or network of neurons are firing and when they are inhibited, that is turned off, that is when the information is processed. So in that case energy consumption is reduced to process the information (at least locally and in the short term). To my knowledge nobody knows yet what the ratio of inhibitory versus excitatory neural networks is although some have estimated that more than half could be inhibitory.
Reply | Report Abuse | Link to thisYes, we don't really need to prove this idea because both it and the opposite can be true. As contributor Krohleder might agree, neuron groups can be like a class of noisy students, processing disjointed trivial thoughts at perhaps relatively high energy expenditure, and when tuned down by an instructor may be directed to a more widespread and coherent attention
Reply | Report Abuse | Link to thisThinking hard does not burn more calories because the brain already burns a lot of calories even when you're not thinking. Some put it at 25 watts. That's 24 hours a day. Put a dynamo to power a 25-watt bulb in your stationary bike. Pedal to keep the lights on for 24 hours. That's how much energy the brain consumes even while you sleep.
Reply | Report Abuse | Link to thisInteresting article however not a single ounce of energy comes from food.
Reply | Report Abuse | Link to thisEnergy comes from the Mind and glucose is the fuel, with oxygen being its burning medium. This accounts for the apparent increase of energy after exercise and the variations in sugar consumption. Not all sugars are made equal, Sugars from fresh fruit and vegetables have the highest nutrient, oxygen and water content hence they are the easiest to digest. Cooked starches on the other hand have far less nutrients and are deprived of the oxygen needed to burn the fuel the body needs in an efficient manner hence the sluggishness and high fluctuations in blood sugar levels.
Energy comes from the fuel which is glucose which comes from food. Energy in the form of electrical signals and heat is expended in the brain.
Reply | Report Abuse | Link to thisExercise increases the rate of metabolism, the conversion of fuel into energy. Sugar is fuel so blood sugar level and energy level in the form of heat are affected by exercise. Notice you feel warm and sweat when exercising.
Reply | Report Abuse | Link to thisNeosteo, I am glad you are interested but almost everything you wrote is somewhat inaccurate. All energy consumption in the body comes from food; specifically sugar. Glucose is type of converted sugar. It is burned to produce heat and adenosine triphosyphate, a molecule that stores and releases energy as needed by the cell. In terms of energy most sugars are sort of equal and I am not sure about what nutrients you mean; but that would have nothing to do with food energy conversion. You do not burn fuel in your body like a combustion engine or fire where oxygen is needed. Also the word nutrient is a vague term which refers to chemicals an organism needs to grow and live. So this can be protein, iron, vitamins, carbohydrates (sugars), etc.
Reply | Report Abuse | Link to this"Energy comes from the Mind and glucose is the fuel, with oxygen being its burning medium."
Reply | Report Abuse | Link to thisYou really need to learn some basic physics. Fuel is the energy source. Try driving your car without gas or batteries. The engine of a vehicle, like the brain in an animal, releases and directs that energy. It does not create that energy. (you can skip the whole steering and transmission bit because I am simplifying)
Had you specified the conversion of potential energy to kinetic energy under the direction of the mind with the potential energy coming from glucose you would have been fine but the way you constructed your sentence creates an incorrect or incomplete statement.
I find it ironic that the first comment I read on this article is such effusive praise, when I found the conclusions to the studies presented rather illogical.
Reply | Report Abuse | Link to thisFor example the article states:
"Complicating matters, some studies have found that when people are not very good at a particular task, they exert more mental effort and use more glucose, whereas at least one study suggests the opposite—that the more skilled you are, the more efficient your brain is and the less glucose you need."
That seems perfectly reasonable to me. When you are not good at something you need to exert more energy and burn more glucose. When you are good at something, you exert less energy and use less glucose. How does that complicate things? The use of the word opposites implies that it's contradictory, but really, it's complementary.
The paragraph about children exercising states;
"children who walked for 20 minutes on a treadmill performed better on an academic achievement test than children who read quietly before the exam. If mental effort and ability were a simple matter of available glucose, then the children who exercised—and burnt up more energy—should have performed worse than their quiescent peers."
Energy in the body isn't in a ready to burn state, like a gas tank. The body has to convert stored energy into usable energy. The kids who were exercising were in energy conversion mode. Their body was freeing stores of glucose to "power" the exercise, so the energy/glucose was more readily available for thinking activities as well.
I think the key points of the topic, which were only lightly touched on at the end, are the sustained concentration required in a situation like the SATs and the duration of time. The studies stated are like comparing a short distance sprinter to a marathon runner.
From all of the research I've read over the years, it appears that the brain does burn significantly more calories while thinking extra hard.
Reply | Report Abuse | Link to thisI think that individuals are too complex in their biology to explain why some feel an increase in appetite after an intense period of studying or whatnot.
Perhaps its from stress or merely just increased hunger.
http://evolutionarypsychiatry.blogspot.com/2010/12/your-brain-on-creatine.html
and http://aging.info
I think there are many things going on in the brain that have not been studied, so the focus on glucose consumption is shortsighted. How about all the neurotransmitters? How about distinguishing between different type tasks? Watching a movie and reading a book are different tasks mentally, very different from performing a math calculation.
Reply | Report Abuse | Link to thisI find it counterintuitive that concentrated thinking would increase energy consumption in the brain. The logic, to me, being that focus on a problem is probably accompanied by inhibition of competing threads of activity. And focus is perceived to be difficult.
Reply | Report Abuse | Link to thisOn the topic of whether mental exhaustion is mostly about energy consumption/availability: The energy that you consume while sleeping for 8 hours is very similar to what you would use if you instead lie awake in bed for the same amount of time. However, the subsequent mental states are of course very different. Wouldn't this suggest that mental exhaustion is not about energy depletion, but is instead connected to somehow not getting the brain "re-set" (or whatever it is that sleep does...)?
Reply | Report Abuse | Link to thisthinking hard is stressful that increases heart rate so prob does increase calorie requirements. http://buysteroidsuk.co/
Reply | Report Abuse | Link to thisI can appreciate certain "theories", however, most are simply that, unless you have good evidence. It's true that brain activity will never compare to moderate types of physical exercise, however, I have been a type 1 diabetic for almost 34 years. I can notice a sizable difference in my blood sugars when consumed in deep thought and having a "mental workout" in a day. I notice the patterns of simular activity in front of the computer, from a day of simple regular work and comparing that with heavy "thinking" days which require constant focus and deep thought (such as drawing up legal and patent papers). The same structured enviroment with the same physical activity (sitting in front of the computer) and thesame diet and insulin usage. However, in a day of deep thought, my sugar can go into the lower ranges several times during the heavy mental days, when n typical days it never does. I can actually feel my pulse if I put my hand on top of my head due to the extra blood flow. So in my own personal experience, I would have to say that heavy thought does burn significantly more calories. Being an insulin dependent diabetic for almost 3 1/2 decades makes me much more sensitive to such changes and I do notice a signifcant difference.
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