Doing challenging work—like figuring out a calculus problem—seems to take a lot of energy, and so it makes your brain feel tired. Spending the same time on Face- book looking at cat pictures doesn’t seem as mentally demanding, because your brain doesn’t use nearly the same amount of energy to do that. Right? Not so fast.
Stress contributes to the feeling of exhaustion you might have after doing challenging work, such as taking a calculus test, where you are worried about your grade and are anxious about your performance. So it’s true that under certain circumstances doing challenging work tires your brain more than easy tasks. But re- search shows that it’s basically your attitude that makes the difference. In other words, you just think that solving the calculus problem is more tiring than looking at cat pictures. As far as how much energy your brain actually uses? There’s not a lot of difference between the two activities.
One study showed that the expectation of mental fatigue actually predicted it. That is, if a person thinks a task will be hard, it often is. So imagine if you changed your attitude. Instead of letting your brain trick you into thinking it’s exhausted, re- mind yourself that those cat pictures are just as hard on it.