Why some people can't resist temptation

Scientists in the US may have come one step closer to understanding why some people are overweight, or have stronger sexual urges than others, based on the way their brain is wired.

Researchers at Dartmouth College in New Hampshire conducted a study on the eating and sex behaviours of 48 university women to research the links between willpower and a part of the brain called the nucleus accumbens, or the brain's key reward center located deep in the striatum.

The women were shown pictures of different stimuli – including food, landscapes and erotic images – while the activity of their accumbens was monitored using functional magnetic resonance imaging (fMRI), which measures brain activity by detecting changes in blood flow to that region.

Six months later, the women returned to fill in a questionnaire and were each weighed to see if they had put on weight.

The scientists discovered that hyperactivity in some women's accumbens to certain stimuli resulted in an increased likelihood of indulgence in those activities, but that the tendencies between sex and food did not cross over.

The results revealed that the women who registered high levels of activity in their accumbens when shown images of food had gained more weight, while the women who responded to erotic images had a stronger sexual appetite and reported having more sex.

Bill Kelley, associate professor of Dartmouth's Department of Psychological and Brain Sciences, said that the research had proven that there are links between this brain region and the exercise of will power.

He said that the stronger a person's reaction to certain stimuli, the less likely they are to "hear" their rational brain telling them "no."

The study's lead researcher Kathryn Demos believes it's not only genetic or environmental influences that affect our temptation for different things, but both.

Demos, who is now an assistant professor of psychiatry and human behaviour at Brown University, said the study shows people have different capabilities when it comes to self-control and that reward "is a very powerful system."

The study was published in this week's edition of the Journal of Neuroscience.