Giving into temptation – whether to cheesecake, cigarettes or drugs – is a common human failing but new findings tie this weakness to a limit in the brain's capacity for resisting temptation.

Too much self-control, the researchers said, may weary the brain.

"I think these findings ground self-control in the brain," said Dr Michael Inzlicht, of the University of Toronto Scarborough in Canada.

Inzlicht and his team, who reported the study in the journal Psychological Science, studied 40 college students. They recorded their brain activity recorded as their capacity for self-control was tested.

First, the students watched a distressing movie. Half were told to try to suppress their emotions while watching the film and show no outward signs of their feelings. The rest were simply told to watch the film carefully.

Immediately afterward, all of the study participants took a test known as the Stroop task. The test requires the subject to look at the words red and green, written in either a red or green font. They then have to identify the word's color, and not the word itself, which requires a form of self-control.

As the students performed the test their brain wave activity was monitored. The researchers found that students who had been asked to control their emotions during the movie did not perform well on the color-naming task. They also showed evidence of weaker activity in an area of the brain called the anterior cingulate cortex (ACC).

"It suggests that the anterior cingulate cortex – a part of the brain that plays a watchtower role, monitoring for goal violations – has its limits," said Inzlicht.

He added that the ACC can become overwhelmed by too many self-control tasks and lose some of its effectiveness. It could manifest itself as an increase in mistakes, or a lack of motivation to tackle a difficult job.

Inzlicht explained that in general, when people try to exercise restraint in one area – sticking with a diet, for example – self-control will likely wane in another area. For the dieter, this could mean difficulty with refusing cigarettes, concentrating on work or keeping emotions in check.

But Inzlicht pointed out that people vary in their natural capacity for self-control. Exercising restraint in many areas of life may be easy for one person, and impossible for another.

More research is needed to understand why people vary in their self-control capacity, and whether this baseline capacity can be increased, Inzlicht said.