We have all experienced that feeling of mental exhaustion after focusing on a tricky problem. Detailed thinking certainly feels like hard work, but is it? The answer is a touch more subtle than you might suspect. Intriguingly, when it comes to energy use, the brain doesn’t distinguish between tasks that we traditionally regard as “hard” and those that come more naturally. This was first demonstrated in the 1950s in a study showing that the brain’s level of metabolism (新陈代谢) is remarkably constant, regardless of whether we are concentrating on mental math or letting our mind wander.
Your brain assigns resources to its different parts depending on the mental activity being carried out. But there is a trade-off. “When the demand of a mentally challenging task increases, you see increased metabolism in the neurons (神经元) responsible for the task,” says Nilli Lavie at University College London. Meanwhile, you see corresponding decreases in other brain areas. For instance, Lavie and her colleagues measured energy use in the brain region responsible for daydreaming and found that it decreased when volunteers carried out a problem-solving task that required focused attention. So thinking hard does burn more energy in the brain region involved, but this is offset by energy savings in other parts of the brain.
However, your brain doesn’t see it that way. “It worries about an imbalance of supply over demand,” she says. When the brain detects exhaustion of glucose (葡萄糖) — the sugar that fuels the brain — in any region, it perceives it as something bad. This is what gives rise to the feeling of being worn out after continuous focus.
So, after a tough exam, the sensation of having burned through a supercomputer’s worth of energy is real, though your brain has used few or no extra calories overall. “There is a constant rate of neural energy in the brain,” says Lavie. “It is irrelevant whether it is spent on a task requiring concentration or on a distraction.”
【小题1】What is the main idea of paragraph 1?| A．We all get tired after hard focus. |
| B．Thinking hard doesn’t use more energy. |
| C．A study shows the brain’s metabolism level. |
| D．Detailed thinking is considered harder than mind wandering. |
| A．It burns an increased rate of calory. |
| B．It stimulates the neurons for the task. |
| C．It’s also involved in the task and requires energy. |
| D．It reduces neural activity and spares more energy. |
| A．Balanced. | B．Absorbed. | C．Dominated. | D．Released. |
| A．The brain detects signals of high energy demand. |
| B．The brain is punishing you for working too hard. |
| C．The brain is losing the balance of energy supplying. |
| D．The brain gets bored easily and refuses to be engaged. |
