Does Thinking Really Hard Burn More Calories?: Scientific American - 0 views
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Just as vigorous exercise tires our bodies, intellectual exertion should drain the brain. What the latest science reveals, however, is that the popular notion of mental exhaustion is too simplistic. The brain continuously slurps up huge amounts of energy for an organ of its size, regardless of whether we are tackling integral calculus or clicking through the week's top 10 LOLcats. Although firing neurons summon extra blood, oxygen and glucose, any local increases in energy consumption are tiny compared with the brain's gluttonous baseline intake. So, in most cases, short periods of additional mental effort require a little more brainpower than usual, but not much more.
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something must explain the feeling of mental exhaustion, even if its physiology differs from physical fatigue. Simply believing that our brains have expended a lot of effort might be enough to make us lethargic.
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a typical adult human brain runs on around 12 watts—a fifth of the power required by a standard 60 watt lightbulb. Compared with most other organs, the brain is greedy; pitted against man-made electronics, it is astoundingly efficient. IBM's Watson, the supercomputer that defeated Jeopardy! champions, depends on ninety IBM Power 750 servers, each of which requires around one thousand watts.
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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.
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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 90-minute computerized test of sustained attention quit pedaling from exhaustion sooner than participants that watched emotionally neutral documentaries before exercising
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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.