I am sure that you have all had this happen before. You have a particularly hard day. Maybe your boss said a few things you disagree with and you had to bite your tongue rather than respond. Or perhaps a friend insulted you, and you had to control yourself in a public place. After all that work controlling yourself, a driver has the nerve to cut you off as you’re trying to make a turn. Suddenly, you are in a honking, yelling, bird-flipping rage.
Research by Roy Baumeister, Kathleen Vohs, and their colleagues suggests that this loss of control is caused by ego depletion. Basically, when you have to spend a lot of time controlling yourself (as you might have to do when you don’t want to confront your boss), that draws on a store of mental resources that you use for self-control. If you drain those resources enough, then eventually they may run out, and you will have trouble controlling yourself further.
The research on ego depletion suggests that it is partly related to energy use in the brain. You can actually measure a drop in blood sugar when people are put in a situation where they have to control themselves. The brain is using extra energy for this self-control. The more energy that people used at one time for self-control, the less likely that those people were to be able to control themselves later.
There is a temptation to say that this self-control causes fatigue. That is, you may literally get tired from having to keep yourself under control. Is this ego depletion the same thing as being tired?
A study I did with Kathleen Vohs, Todd Maddox, and Brian Glass that was published in the journal Social Psychological and Personality Science in 2011 set out to explore this question. This experiment was run as part of a larger study looking at the effects of sleeplessness on performance. As a part of this study, participants were kept awake for 36 hours. They underwent a number of tests in this period.
In this study, we manipulated whether people had to do a difficult task of self-control. We asked people to watch a couple of videos that were disgusting and/or funny. One disgusting video was a scene from the movie Trainspotting in which the main character has to dig through a dirty toilet to find drugs that had been dropped in it. The video that was disgusting and funny was the scene from Monty Python’s Meaning of Life where a morbidly obese character finishes a huge meal and then vomits everywhere.
The group that had to do difficult self-control watched the scenes and had to keep a straight face through the whole thing so that someone observing them would not know what kind of scene they were watching. The other group just watched the scenes. Some people did this experiment when they had only been awake for 12 hours (so they were pretty fresh). Others did it when they had been up for over 24 hours (so they were pretty tired).
After watching the movie clips, people played a “noise blast” game that is often used in psychology studies as a test of aggression. Basically, you play against a partner. The winner of each round of the game gets to punish the other player by blasting them with noise. The louder the noise you choose to blast your partner with, the more aggressive you are being in the game.
We found that people who had to keep a straight face while watching the film clips were more aggressive than the people who just watched the film clips. So, a difficult self-control task made it difficult to exhibit self-control later. But, the amount of sleep you had didn’t matter. That is, people who were fresh were no more or less aggressive than people who were sleepless. These results suggest that being worn out from having to do a lot of self-control is not the same thing as being tired from lack of sleep.
So, what can you do when you have had a hard day?
One thing that is helpful is to do things that will give you energy. Eat some food, or drink some juice. Take a walk in the sunshine or do some exercise. When you have had a tough day, don’t make the bad day worse by rushing from one stressful situation into another.