Two patients with rare lesions to the brain have provided direct of evidence of how we make decisions - and what makes us dislike the thought of losing money.

Researchers at the California Institute of Technology studied a phenomenon known as 'loss aversion' in two patients with lesions to the amygdala, a region deep within the brain involved in emotions and decision-making.

Loss aversion describes the avoidance of choices which can lead to losses, even when accompanied by equal or much larger gains. Examples in the everyday life include how we make a decision on whether to proceed with an operation: the more serious the potential complications from the operation - even if the risk is low compared to the chances of success - the less likely we would be to proceed.

It even has implications on organ donation rates - if people are required to 'opt-in' to a system, they are less likely to move away from the default option.

Dr Benedetto De Martino, a Sir Henry Wellcome Trust Postdoctoral Fellow and first author of the report, explains: "Imagine you're on Who Wants to Be a Millionaire. You've just answered the £500,000 question correctly and have moved on to the final question. You're down to your 50:50 lifeline but don't know the answer.

If you get it right, you'll win £1 million; if you get it wrong, you'll drop back to £32,000. The vast majority of people would take the 'loss averse option' and walk away with £500,000."

This new study has explored whether loss aversion is mediated by the amygdala, as is currently hypothesised. The researchers studied two patients affected by a rare genetic condition which has led to the formation of lesions to the amygdala.

These lesions prevent the patients from perceiving, recognising or feeling fear. For example, the patients can recognise all other emotions in a person's face, but if shown a fearful face they cannot say what emotion that person is experiencing.

Each patient - together with twelve 'healthy' controls - took part in a task designed to test whether the chance of losing money affected people's likelihood to gamble

Source: Wellcome Trust