People who make irrational decisions when faced with problems are at the mercy of their emotions, a study says.
Emotions govern irrational decisions, researchers found
Researchers traced the origin of such decisions to the brain's emotion centre, the amygdala, in a study of 20 people using a gambling game.
That brain region fires up in people faced with a difficult situation but reactions to its effects vary, the University College London team found.
The study findings were published in the Science journal.
The researchers found some people kept a cool head and managed to keep their emotions in check, while others were led by their emotional response.
In each trial, participants motivated by the promise of real money were first offered a starting amount of £50.
They were then presented with one of two "sure option" choices, either to "keep £20", or to "lose £30", as well as the opportunity to take an all-or-nothing gamble.
Although both sure options left players with the same amount of cash, £20, people were more likely to gamble when faced with the prospect of losing £30.
Given the "keep £20" option, volunteers played it safe and gambled only 43% of the time.
When asked if they wanted to "lose £30", they gambled on 62% of occasions.
The decision to gamble was irrational, since in every case the amount of money they stood to gain was the same, while everything could be lost by gambling.
Brain scans revealed that the amygdala fired up when subjects either chose to keep a sure gain or decided to gamble in the face of certain loss.
The brain region, which controls emotion and plays a role in the "fight or flight" reaction to perceived threats, appeared to be pushing people to keep sure money, or to gamble instead of losing.
In both situations an emotional reaction was involved, which in the case of gamblers triggered an irrational response.
Lead researcher Benedetto de Martino said: "It is well known that human choices are affected by the way in which a question is phrased.
"Our study provides neurobiological evidence that an amygdala-based emotional system underpins this biasing of human decisions.
"Moreover, we found that people are rational, or irrational, to widely differing amounts."
He said the amygdala was active in all participants, regardless of whether they behaved rationally or not.
In more rational individuals there was greater activation of the orbitofrontal cortex, a part of the brain which deals with higher executive functions such as reasoning and planning.
This suggested that people who behaved rationally were better able to manage or override their emotional responses.