It turns out that making decisions is tiring and wears us out, more so than other (similarly difficult) mental tasks. At this point, a large body of research shows that whenever we make many choices in a row, the quality of our decisions gets worse over time.
Examples: one study looked at more than a thousand parole decisions made by experienced judges at an Israeli prison. At the beginning of the day, the judges were likely to give a favorable ruling about 65 percent of the time. As the morning wore on, the likelihood of a criminal getting a favorable ruling steadily dropped to zero. After the lunch break, however, the likelihood of a favorable ruling would immediately jump back up to 65 percent. And then, as the hours moved on, the percentage of favorable rulings would fall back down to zero by the end of the day. Regardless of the crime, a prisoner was much more likely to get a favorable response if their parole hearing was scheduled either early in the morning or immediately after a food break, than if it was scheduled near the end of a long session. In other words, the outcome of a decision was highly influenced by how many decisions the judges had already made previously.
Experimental studies have also shown that people are less able to exert self-control after making a series of choices. In one experiment people made choices among consumer goods or college course options, whereas others thought about the same options without making choices. Making choices led to many different forms of reduced self-control afterwards: less physical stamina, reduced persistence in the face of failure, more procrastination, and poorer performance on math problems. It is noteworthy that making actual decisions seemed to wear people out a lot more than just thinking about options.
Decisions that are especially taxing are those that involve self-control. For example, when people fended off the temptation to eat M&M’s or freshly baked chocolate-chip cookies, they were then less able to resist other temptations later on.
Self-control tasks and decisions also require more glucose in the brain than other mental tasks. Low or hypoglycemic levels of glucose lead to impaired decision making, poor planning, and inflexible thinking. In contrast, simple psychomotor abilities, such as responding quickly to certain cues, seem relatively unaffected by glucose levels.
This pattern is in line with other things we know about impulsive behavior and typical self-control problems. For example, research on addiction and criminal behavior suggests that self-control failure is most likely during times of the day when glucose is used least effectively, and when people are tired. We also know, for example, that alcohol reduces glucose throughout the brain and body and likewise impairs many forms of self-control.
What is it about decision-making and self-control in particular that makes them so susceptible to glucose?
The answer to this question is still somewhat controversial. One reason is probably that since self-control processes are so costly, requiring larger amounts of glucose than other tasks, they’re also be the first to be impaired when glucose drops. Another reason could be that when glucose drops, the brain functions that are most central to survival (e.g., breathing, physical coordination) have first dibs on available glucose, not leaving enough for more advanced mental operations.Both of these ideas are consistent with the general rule that abilities that developed last are the first to become impaired when resources are limited. Self-control, planning and decision-making are all processes that involve the frontal areas of the brain – the pre-frontal cortex, to be specific. This area is the most recently developed part of our brain in evolutionary history, and it is also the part that takes longest to mature fully in human adolescents and young adults. What does this mean for us?
While metabolically healthy adults can fast without their blood glucose levels being affected, they still need rest to recover from decision fatigue. Sleep and rest replenish the ability to exert self-control.
The finding that that our psychomotor abilities are not as easily impaired as our abilities for judgment and decision-making suggests that we may often not realize our impairment, because the very capacity (judgment!) that we would need to recognize it is the first one to be impaired. This means planning is essential!
- Get enough breaks, rest and sleep
- Avoid making important decisions when tired
- Plan ahead to get into healthy routines
by Ursina Teuscher at Teuscher Counseling, LLC
References:
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