The reason why some people gamble may be explained by brain chemistry, according to a recent US study.

While most people do not choose to gamble away their life savings, some do, and the reason may be to do with part of the brain called the amygdala.

The amygdala, which takes its name from its almond shape, plays a key role in the decision making process.

Some people whose amygdalas are damaged are no longer able to avoid gambling in situations where the odds are stacked against them, because they lack access to a process known as risk aversion.

For the purposes of the study, the research team examined two women whose amygdalas had sustained heavy damage.

In both women, risk aversion was very reduced compared with people their own age.

Lead author Benedetto De Martino, of the California Institute of Technology in the US, said that functional magnetic resonance imaging (fMRI) had led him to suppose that the amygdala played a crucial part in human risk aversion, although he was not certain this was the case until he studied the two brain-damaged women.

The two women differed from the other study subjects in that they were willing to gamble without considering the relative odds of loss and gain.

Martino said that the older of the two women he studied tended to seek out loss.

He said that he believed this could be because people's amygdalas shrink as they age, or because the fact that they do not have as many years to live means they are less careful about life changes.

He said that animals use loss-aversion to protect themselves from predators, and that the amygdala helped people to protect themselves from losing money, which was an extension of that function.

Martino said that he hoped his studies would help construct a more biological view of social sciences, and that he had previously done research on the way people with amygdala damage make decisions generally.

The two brain-damaged women who participated in the study both had a rare condition that produced amygdala lesions and left the rest of their brains intact.

John Aggleton, a Professor of Psychology at Cardiff University, said that the finding was the result of a very elegant and neat experiment.

He said that the study showed very clearly that when the amygdala had been damaged, loss aversion disappeared.