The study, to be published in Nature today, shows that decisions about what to buy and what not are made by a few neurons located in the orbitofrontal cortex (OFC), an area of the brain just behind the eyes.

“We have long known that different neurons in various parts of the brain respond to separate attributes, such as quantity, colour and taste,” said Camillo Padoa-Schioppa, the neurobiologist who led the study. But quite how those different attributes are reconciled has been a mystery until now.

You might, for example, like one shirt because it is blue, but another because of its texture and another for its size. How do you choose between them or to buy any of them at all?

To find out, Padoa-Schioppa and his colleagues studied the brain activity of macaque monkeys who were offered the choice between grapefruit juice and orange juice in differing quantities. The monkeys generally preferred grapefruit juice, but opted for orange juice under certain circumstances — if, for example, a sufficiently greater quantity was available.

When three times more orange than grapefruit juice was offered, the monkeys switched their choice.

What Padoa-Schioppa found was that while different areas of the brain are involved in taste, the decision to change the choice was made by a few neurons in the OFC. Any small lesions or damage to that area could cause shoppers to behave irrationally, he said. “When you go to compulsive shopping, I think it is safe to assume that there is a dysfunction in the OFC which is leading to it.”

Such dysfunctions may be involved in other addictions as well. “In various brain scans, when people gamble, we see the OFC light up. Similarly, drug addiction is a type of impulsive behaviour.”

One woman who has experienced the compulsion to shop non-stop is Juliana De Angelis, a sales rep from west London. “I used to be buying something nearly every day,” said De Angelis, who in the past bought items of clothing or jewellery every other day. “It’s just this thing where I have to buy something. It’s a force stronger than me. I can’t control it.”

Coleen McLoughlin, fiancée of the England footballer Wayne Rooney, has become a national emblem of shopaholism. The 20-year-old has been known to spend £15,000 in one weekend on shopping sprees in New York.

The American Psychiatric Association has previously concluded that “compulsive shopping” is not a specific mental disorder. Instead, some experts see it as an addiction associated with low self-esteem.

The findings from Padoa-Schioppa’s research may shed new light on the debate. The discovery that the OFC is required to balance complex competing demands from different parts of the brain also chimes with a new survey that shoppers are being swamped by choice.

One in three is so bamboozled by the range of goods on offer that the would-be shopper avoids large stores or leaves without buying anything. According to an ICM poll last week, half of all customers over 65 said that the choice offered in supermarkets is “overwhelming”. Tesco sells more than 50 types of bread roll and Waitrose nearly 50 types of sugar.

“While generally consumers will say yes to more choice, if you keep adding to the range without managing it, it is a recipe for disaster,” said Richard Wildman of the business consultancy Accenture. One reason Marks & Spencer has improved its sales, said a spokesman, is because it has reduced excessive choice.

The latest US study also threw up another intriguing finding: when monkeys were asked to choose between juices, their decision was not affected by the way the juice was offered.

It did not matter in which order the juices were placed: the monkeys still made a calculated choice based on the values they had established. If there was at least three times more orange juice, they would choose orange whatever its position.

“This result has broad implications for possible psychological models of economic choice,” said Padoa-Schioppa.

In other words, all that supposedly clever placing of certain items on high or low shelves, or near the front or back of shops, may not be as influential as retailers believe.

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