But the brain must actively maintain appropriate concentrations of charged particles across the membranes of billions of neurons , even when those cells are not firing. Because of this expensive and continuous maintenance, the brain usually has the energy it needs for a little extra work. Authors of other review papers have reached similar conclusions. Robert Kurzban of the University of Pennsylvania points to studies showing that moderate exercise improves people's ability to focus.
In one study, for example , 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.
The influence of a mental task's difficulty on energy consumption "appears to be subtle and probably depends on individual variation in effort required, engagement and resources available, which might be related to variables such as age, personality and gluco-regulation," wrote Leigh Gibson of Roehampton University in a review on carbohydrates and mental function.
Both Gibson and Messier conclude that when someone has trouble regulating glucose properly—or has fasted for a long time—a sugary drink or food can improve their subsequent performance on certain kinds of memory tasks. But for most people, the body easily supplies what little extra glucose the brain needs for additional mental effort. Body and mind If challenging cognitive tasks consume only a little more fuel than usual, what explains the feeling of mental exhaustion following the SAT or a similarly grueling mental marathon?
One answer is that maintaining unbroken focus or navigating demanding intellectual territory for several hours really does burn enough energy to leave one feeling drained, but that researchers have not confirmed this because they have simply not been tough enough on their volunteers. In most experiments, participants perform a single task of moderate difficulty, rarely for more than an hour or two.
Equally important to the duration of mental exertion is one's attitude toward it. Watching a thrilling biopic with a complex narrative excites many different brain regions for a good two hours, yet people typically do not shamble out of the theater complaining of mental fatigue. Some people regularly curl up with densely written novels that others might throw across the room in frustration. Completing a complex crossword or sudoku puzzle on a Sunday morning does not usually ruin one's ability to focus for the rest of the day—in fact, some claim it sharpens their mental state.
In short, people routinely enjoy intellectually invigorating activities without suffering mental exhaustion. Such fatigue seems much more likely to follow sustained mental effort that we do not seek for pleasure—such as the obligatory SAT—especially when we expect that the ordeal will drain our brains.
If we think an exam or puzzle will be difficult, it often will be. Studies have shown that something similar happens when people exercise and play sports: a large component of physical exhaustion is in our heads. In related research, volunteers that cycled on an exercise bike following a minute computerized test of sustained attention quit pedaling from exhaustion sooner than participants that watched emotionally neutral documentaries before exercising. Even if the attention test did not consume significantly more energy than watching movies, the volunteers reported feeling less energetic.
That feeling was powerful enough to limit their physical performance. In the specific case of the SAT, something beyond pure mental effort likely contributes to post-exam stupor: stress.
After all, the brain does not function in a vacuum. Other organs burn up energy, too. Taking an exam that partially determines where one will spend the next four years is nerve-racking enough to send stress hormones swimming through the blood stream, induce sweating, quicken heart rates and encourage fidgeting and contorted body postures.
The SAT and similar trials are not just mentally taxing—they are physically exhausting, too. 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. As described by the American Heart Association AHA , "Your body releases adrenaline, a hormone that temporarily causes your breathing and heart rate to speed up and your blood pressure to rise.
These reactions prepare you to deal with the situation. But though crying is a physical response, it is not physical exercise. It doesn't burn significant calories, nor is it likely to help you reach a weight-loss goal. As the AHA makes clear, the only muscle that emotional stress really "burns" per se is the heart. And even though your heart rate does speed up when you are sobbing due to grief or anguish, that increase isn't enough to have a significant impact on your metabolic rate — or result in weight loss.
Another point to consider is that mental and emotional stress can both result in emotional eating, which adds calories instead of burning them. Bottom line: If you are trying to lose weight, draining your energy by overloading your brain or emotions isn't going to produce results. It might even make you overeat, or feel too worn out to engage in healthful forms of exercise.
Frequent crying and changes in appetite are two signs of clinical depression, according to the Skidmore College Counseling Center. If you or a loved one have been experiencing them for more than a few days, talk to a mental health professional.
By Elizabeth Kuster Updated October 4, Elizabeth Kuster. To put cranial calorie burn in perspective, it helps to understand how your body burns energy. And no part of you demands more energy than your brain. Different mental states and tasks can subtly affect the way the brain consumes energy.
A person doing cognitively challenging work for eight hours would burn about more calories than a person watching TV or daydreaming for the same amount of time, he estimates. Drinking Gatorade or gobbling a few jelly beans could replenish your glucose stores and help restore your brain to full power. However, there could still be a calorie-burning upshot for people who spend their days performing mentally challenging work. Contact us at letters time. Here's What the Science Says.
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