Sussex university academic discover 'foodie' switch in brain

A single bad experience with food usually leaves people unable to stomach the thought of eating that particular dish ever again - and scientists wanted to know why.

They believe such bad experiences could be causing a switch in our brains which affects our future eating habits such as whether to give gherkins a second chance or risk another takeaway Vindaloo.

The findings come from a study on hungry snails which refused to each sugar, after forming a negative association with it, and snacked on cucumber instead.

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Study senior author Professor George Kemenes, of the University of Sussex, said: "Snails provide us with a similar yet exceptionally basic model of how human brains work.

"In our research, the negative experience the snail had with the sugar could be likened to eating a bad takeaway curry which then puts us off that particular dish in future.

"We believe that in a human brain, a similar switch could be happening where particular groups of neurons reverse their activity in line with the negative association of a particular food. "

Like many other animals, snails like sugar and usually start feeding on it as soon as they come across it.

But through training, which involved tapping the snails gently on the head when sugar appeared, the snails' behaviour changed and they refused to eat sugar even when hungry.

When researchers presented the trained snails with a piece of cucumber instead, they found that the animal was still happy to eat the healthy option.

This shows that the taps were associated with only the sugar that they were trained to reject.

Looking at little closer, the team discovered activity in the brain that reversed the snails' usual response to sugar after the training had taken place.

Professor George Kemenes works at the University of Sussex

Dr Ildiko Kemenes, reader in neuroscience at the University of Sussex, said: "There's a neuron in the snail's brain which normally suppresses the feeding circuit.

"This is important, as the network is prone to becoming spontaneously activated, even in the absence of any food.

"By suppressing the feeding circuit, it ensures that the snail doesn't just eat everything and anything.

"But when sugar or other food stimulus is present, this neuron becomes inhibited so that feeding can commence.

"After the aversive training, we found that this neuron reverses its electrical response to sugar and becomes excited instead of inhibited by it.

"Effectively, a switch has been flipped in the brain which means the snail no longer eats the sugar when presented with it, because sugar now suppresses rather than activates feeding."

Scientists say the effect of the neuron which suppresses the snail's feeding circuit is similar to how the human brain works.

In parts of the human brain, networks are kept under control to avoid 'runaway' activation which may lead to overeating and obesity.

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Further findings revealed that when the neuron was removed entirely from trained snails, they returned to eating sugar again.

Dr Ildiko Kemenes added: "This suggests that the neuron is necessary for the expression of the learned behaviour and for altering the response to sugar.

"However, we cannot rule out that the sugar-activated sensory pathway also undergoes some changes, so we don't make the assumption that this is all that's happening in the brain."

The research, funded by the Biotechnology and Biological Sciences Research Council, was published in the journal Current Biology.