The brain is like a muscle: when it gets depleted, it becomes less effective.

By On Amir

Scientific American

 The human mind is a remarkable device. Nevertheless, it is not without limits. Recently, a growing body of research has focused on a particular mental limitation, which has to do with our ability to use a mental trait known as executive function. When you focus on a specific task for an extended period of time or choose to eat a salad instead of a piece of cake, you are flexing your executive function muscles. Both thought processes require conscious effort-you have to resist the temptation to let your mind wander or to indulge in the sweet dessert. It turns out, however, that use of executive function—a talent we all rely on throughout the day—draws upon a single resource of limited capacity in the brain. When this resource is exhausted by one activity, our mental capacity may be severely hindered in another, seemingly unrelated activity. (See here and here.)...[more]

 

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Unfortunately no references are given with the article. The following appears in a comment:

More on Kathleen Vohs and the 2008 paper found at: http://www.csom.umn.edu/Page6301.aspx "Making Choices Impairs Subsequent Self-Control: A Limited-Resource Account of Decision Making, Self-Regulation, and Active Initiative," Kathleen D. Vohs, Roy F. Baumeister, Brandon J. Schmeichel, Jean M. Twenge, Noelle M. Nelson, and Dianne M. Tice, Journal of Personality and Social Psychology (May 2008). CW