It would explain why someone who works very hard not to take a second helping of lasagna at dinner winds up taking two pieces of cake at desert. The study could also modify previous thinking that considered self-control to be like a muscle.
University of Iowa neuroscientist William Hedgcock confirms previous studies that show self-control is a finite commodity that is depleted by use. Once the pool has dried up, we're less likely to keep our cool the next time we're faced with a situation that requires self-control.
But Hedgcock's study is the first to actually show it happening in the brain, using Functional Magnetic Resonance Imaging (FMRI) images that scan people as they perform self-control tasks, the Journal of Consumer Psychology reports.
The images show the anterior cingulate cortex (ACC) fires with equal intensity throughout the task. ACC is the part of the brain that recognises a situation in which self-control is needed and says: "Heads up, there are multiple responses to this situation and some might not be good."
However, the dorsolateral prefrontal cortex (DLPFC) fires with less intensity after prior exertion of self-control. DLPFC is the part of the brain that manages self-control and says: "I really want to do the dumb thing, but I should overcome that impulse and do the smart thing".
Hedgcock said that loss of activity in the DLPFC might be the person's self-control draining away. The stable activity in the ACC suggests people have no problem recognising a temptation. Although they keep fighting, they have a harder and harder time not giving in.
Researchers gathered their images by placing subjects in an MRI scanner and then had them perform two self-control tasks-the first involved ignoring words that flashed on a computer screen, while the second involved choosing preferred options.
Hedgcock says the study is an important step in trying to determine a clearer definition of self-control and to figure out why people do things they know aren't good for them.
One possible implication is crafting better programs to help people who are trying to break addictions to things like food, shopping, drugs, or alcohol.