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Scientists have identified a brain region that ensures most people avoid taking reckless risks with money.

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When it is not working properly a person is more likely to throw caution to the wind - both in real life and on game shows.

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The amygdala consists of two almond-shaped tissue clusters buried deep within the brain.

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In the past it has been associated with feelings and perceptions of fear, and the ability to empathise.

The new study led by a British scientist in the US indicates that the amygdala is closely tied to an in-built fear of losing money.

The evidence comes from two patients with rare amygdala injuries who displayed an unusual disregard for how much they stood to lose when taking part in a gambling game.

Benedetto De Martino, a visiting researcher from University College London working at the California Institute of Technology (Caltech), said: "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."

The patients with brain damage, two women aged 43 and 23, showed that they lacked this cautionary instinct when their behaviour was compared with that of 12 healthy individuals.

Scientists devised a "game" to test whether the chances of losing money affected the study participants' willingness to gamble.

At the start of the experiment each volunteer was given 50 dollars with which to gamble on the outcome of tossing a coin. They had a 50/50 chance of winning or losing, but each time the coin was flipped the amount they stood to win or lose was altered.

As expected, healthy individuals were less likely to gamble when the difference between potential winnings and losses was smaller. They were more likely to gamble for a win of 50 dollars if they risked losing 10 dollars than if they stood to win only 20 dollars at the risk of losing 15 dollars.

However the two women with amygdala injuries did not behave the same way and were much less likely to balance potential gains and losses. Even when the amount they could lose outweighed the amount they could win, they chose to gamble.

Professor Ralph Adolphs, a member of the Caltech team, said: "A fully functioning amygdala appears to make us more cautious. We already know that the amygdala is involved in processing fear, and it also appears to make us 'afraid' to risk losing money."

The amygdala may control a general biological mechanism that inhibits risky behaviour that can lead to negative outcomes, the scientists believe.

The study, published in the journal Proceedings of the National Academy of Sciences, also demonstrated that amygdala-mediated "loss aversion" was not the same as "risk aversion".

A variant of the gambling game showed little difference between the brain damaged patients and healthy volunteers when they were faced with a choice of winning either something or nothing.

The research was part-funded by the Wellcome Trust charity.