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Six morbidly obese people have agreed to take part in a clinical trial of a brain chip that zaps them when they think about food.

The chip, known as a responsive neurostimulation system (RNS), was originally developed by medical technology company NeuroPace to treat people with epilepsy.

Once implanted in the brain, it records brain activity continuously, and delivers a mild electric shock whenever it detects a specific pattern of activity that signals the onset of a seizure.

This shock is designed to stop the seizure before it begins.

A recent research study published in the Proceedings of the National Academy of Sciences demonstrated that the same technique could be used to suppress binge-eating behaviour in mice.

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Now scientists at Stanford University want to find out if it could also work on humans who suffer from what is known as "loss-of-control eating".

The clinical trial , which will take place over five years, will see six participants have the RNS chip implanted in their brains for at least 18 months at a time.

The chip will monitor brain activity for six months before turning on the stimulation, in an attempt to identify the pattern of activity that signals the start of a food binge.

The goal is first to determine if the procedure is feasible and safe, and then, hopefully, effective.

The scientists stress that the procedure is not intended for people who are trying to lose a little bit of weight.

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To be eligible for the study, people must have a body mass index (BMI) of over 45 and not have lost weight from gastric bypass surgery or cognitive behavioural therapy.

"These are patients who are essentially dying of their obesity," Stanford's Dr Casey Halpern told Medium's health outlet Elemental .

Other clinical trials have used a similar approach called deep brain stimulation (DBS) to try to treat obesity.

However, DBS, which is most commonly used to treat Parkinson's disease, delivers a continuous electrical current, whereas RNS emits a shock only when it detects the target pattern of activity.

The earlier trials also focused on an area of the brain called the hypothalamus, which controls hormone levels involved in feelings of hunger and satiety, as well as the body's metabolism.

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But Halpern is focusing on an area called the nucleus accumbens - the brain's pleasure centre, which is integrally involved in feelings of reward and addiction.

"There is a lot of evidence to suggest the nucleus accumbens is an important target," said Dana Small, a professor of psychiatry and psychology at Yale University, who is not involved in the study.

"There are many studies looking at brain response to food cues, and the nucleus accumbens is very frequently activated and associated with all kinds of factors that are associated with risk for overeating or developing obesity."

The challenge, according to the scientists, will be separating the brain's response to fatty foods from its response to healthy foods, and from other feelings of reward.

There is also concern that the stimulation could cause feelings of depression or anhedonia - a loss of interest in things and a general inability to experience pleasure.