April 06, 2008
Brain Willpower Depleted By Use

The more you exercise your willpower in one area the less willpower you have left for other purposes.

The brain’s store of willpower is depleted when people control their thoughts, feelings or impulses, or when they modify their behavior in pursuit of goals. Psychologist Roy Baumeister and others have found that people who successfully accomplish one task requiring self-control are less persistent on a second, seemingly unrelated task.

In one pioneering study, some people were asked to eat radishes while others received freshly baked chocolate chip cookies before trying to solve an impossible puzzle. The radish-eaters abandoned the puzzle in eight minutes on average, working less than half as long as people who got cookies or those who were excused from eating radishes. Similarly, people who were asked to circle every “e” on a page of text then showed less persistence in watching a video of an unchanging table and wall.

The article reports you can keep up your willpower by keeping up your blood sugar. Also, exercising your willpower appears to make it stronger.

These claims seem consistent with my own daily experience. I have to let some things slide in order to get through dealing with people and chores in other areas.

The writers of this New York Times article, Sandra Aamodt, editor of Nature Neuroscience, and Sam Wang, a prof of biology and neuroscience at Princeton, have a new book that sounds interesting: “Welcome to Your Brain: Why You Lose Your Car Keys but Never Forget How to Drive and Other Puzzles of Everyday Life.”.

The research literature on brain metabolism and willpower is fascinating. For example, people who try to suppress facial expressions while watching a movie have lower blood sugar as a result. That lower blood sugar means less glucose available for the brain to do additional cognitive processing.

Self-control literally requires energy. Subjects asked to suppress facial reactions (e.g. smiles) when watching a movie have lower blood glucose levels, suggesting higher energy consumption. Control subjects (free to react how they want) had the same blood glucose levels before and after the movie, and performed better than control subjects on a Stroop Task. Restoring glucose levels with a sugar-sweetened lemonade (instead of artificially-sweetened beverages, without glucose) also increases performance. Self-control failures happen more often in situation where blood glucose levels is low. In a literature review, Gailliot et al show that lack of cognitive, behavioral and emotional control is systematically associated with hypoglycemia or hypoglycemic individuals. Thought suppression, emotional inhibition, attention control, and refraining from criminal behavior are impaired in individual with low-level blood glucose (Gailliot & Baumeister, 2007).

Matthew T. Gailliot and Roy F. Baumeister of Florida State University wrote a pretty good review of the relationship between glucose and willpower in 2007: The Physiology of Willpower: Linking Blood Glucose to Self-Control (PDF format).

Attention control is a pervasive and basic form of self-control. Executive control can dictate and choose what information is noticed and processed by the mind, as opposed to letting salience and the environment dictate. In a review of the literature on self-regulation, Baumeister et al. (1994) observed that attention appears to be the front line of control for many problem behaviors, and loss of attention control is a precursor to self-control failure in many different domains. Controlling attention requires self-control because attention automatically orients toward various stimuli in the environment (e.g., Shiffrin & Schneider, 1977). It takes self-control to override these automatic responses so as instead to remain focused on any single task or stimulus (Muraven & Baumeister, 2000). Consistent with the idea that attention control depletes the same energy needed for self-control, research has shown that people are less able to exert self-control after having controlled their attention and that they are less able to control their attention after having exerted self-control (e.g., Vohs et al., 2005; Gailliot & Baumeister, in press; Gailliot et al., 2006; Vohs & Faber, 2004).

One study found evidence consistent with the idea that attention control requires a relatively large amount of glucose (Gailliot, Baumeister, et al., 2007). Participants watched a 6-min video that required them either to control their attention by ignoring certain stimuli appearing on the screen or to watch the video as they would normally, thus not trying to control their attention. Among participants who had controlled their attention, glucose dropped after having watched the video. Among participants who watched without controlling attention, glucose levels did not change. The implication is that controlling attention resulted in the consumption of relatively large amounts of glucose. To be sure, it is more difficult to watch the video while controlling attention than while watching it without such effort, and participants’ ratings of task difficulty confirmed that difference. Self-control requires effort, and that makes it difficult. From this and similar studies, it is not easy to infer whether the differences are due to self-control per se or to the general difficulty of performing the task.

They report that diabetics and those with hypoglycemia have poorer attention control.

If you want to maintain good attention control and willpower then eat your breakfast. Also, eat low glycemic index food.

Share |      Randall Parker, 2008 April 06 09:10 PM  Brain Limits

km said at April 8, 2008 10:58 PM:

Mmmm, radishes. I love radishes.

JussiR said at April 12, 2008 3:05 AM:

When we have autonomic response to something only very small parts of the brain that have learned that response need to activate. Where as when we use our willpower to choose some novel response that we haven't used before in the same sitsuation, we need to activate much more broader area to find that correct response. In that sense willpower (~conscious effort?) could be associated with more brain activation, which would also explain the increased need for glucose. Probably also shutting down the automatic response requires some activation of inhibitive networks. I'm not big fan of brain scan research, but in this question it might reveal some interesting results.

Mr Ian said at April 12, 2008 3:55 AM:

I have been following this guy and his studies peripherally for some months. I work in forensic mental health and am very interested in the potential application of this theory in mentally disordered offenders. Given that people with major psychoses (eg schizophrenia) do not commit offences because of the experiences but because of a lack of ability to maintain threat-control override; my hypothesis would be something along the lines of how the capacity of willpower is depleted by mental health symptoms and how this might be reverted to provide sufferers with bolstered will power to avoid offending behaviours. Blood glucose monitoring is an interesting place to start as it is well known that one symptom of those with low blood sugars is aggressive behaviours.

Axel said at May 6, 2011 10:32 AM:

This new study contradicts the one mentioned here:
Brain’s willpower not fueled by glucose

Abon dotmanon said at January 2, 2012 9:56 PM:

Using radishes ruins the study, since we don't know if the real reason the participants that ate the radishes could not maintain the same level of attention on their next task might not have due to their herculean efforts in trying not fart in public.

I mean it's a well known fact that radishes cause tremendous flatulence, trying to suppress a fart can be very distracting and could have made it very difficult for the radish eaters to persevere on their tasks as their stomachs churned and their colons inflated with putrid gases (radish farts are extra stenchful & noxious due to fermentation by intestinal bacteria of indigestible sugars and soluble fibers found in radishes). One can imagine that the radish-eating participants might have been focussing the majority of their attention and efforts on keeping their anal sphincters and butt-cheeks closed tightly to prevent the explosive expulsion of sulfurous radish fart gases building up in their colons.

The study authors should have used a more neutral placebo, such as iceberg lettuce or celery; but fart and gas inducing radishes pooches the study with extraneous factors; therefore no meaningful conclusion can be derived.

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