Bad experiences with food, such as an unreliable curry that makes us sick for days, cause a switch in our brain that makes us never want to eat it again, a study shows.
British researchers have managed to mimic the effect of a negative experience on eating behavior by using sugar-loving snails as a model in the laboratory.
They used “aversive training,” patting the snails on the head during filming when sugar appeared, as an indication of food poisoning in humans.
Aversive training flipped an appetite-suppressing switch, causing the snails to refuse to feed on the sugar even when hungry.
The experts believe that something similar is happening, leading to “sustained physiological change” specific to a particular food for the rest of our lives.
That dodgy chicken tikka masala from four years ago may make us never want to eat the dish again – and researchers think they know why
“In fact, a switch in the brain has flipped, meaning that the snail no longer eats the sugar when presented with it, because sugar now suppresses feeding rather than activating it,” said study author Dr. Ildiko Kemenes of the University of California. Sussex.
Snails love sugar and usually start eating it as soon as they get it, just like humans when they see sweet treats in the kitchen.
“Snails provide us with a similar but exceptional basic model of how human brains work,” said Professor George Kemenes, also at the University of Sussex.
“In our study, the negative experience the snail had with the sugar could be compared to eating a bad takeaway curry, which will get us rid of that particular dish in the future.”
Despite their primitive looks and reputation, there is a switch in snail brains that actually prevents them from overeating.
Bad experiences with food, like an unreliable curry that makes us sick for days, trigger a switch in our brain that makes us never want to eat it again, study reveals
This appetite suppressant switch (ASD) is controlled by a neuron – a type of highly excitable cell that sends information to parts of the body through electrical signals.
“There is a neuron in the snail brain that normally suppresses the feeding circuit,” said Dr. Ildiko Kemenes.
‘That is important, because the network can be activated spontaneously, even if there is no food.’
‘By suppressing the feeding circuit, it ensures that the snail does not just eat everything.’
Researchers think something similar is going on in the human brain, which is considered a natural tactic to protect us from obesity (although it is likely that some people’s appetite-suppressing switches work better than others).
Usually, when food is present, this neuron in the snail brain is inhibited so that feeding can begin.
After the hungry snails’ aversive training, researchers found that this neuron reversed its electrical response to sugar and became aroused rather than inhibited by it.
That increased activity of the excited neuron essentially turned on the ASD, suppressing snails’ appetite.
Most importantly, this effect was only seen with sugar – so the researchers compared it to the lasting psychological effects of people eating a specific meal that makes them sick.
Researchers placed snails in Petri dishes and exposed them to sugar and ‘strong touch stimuli to the head’
When researchers gave the trained snails a piece of cucumber instead, they found that the animal still liked to eat it.
This showed that the gentle head taps during aversive training were only related to the specific type of food present at the time.
“We believe that in a human brain a similar switchover could take place where certain groups of neurons reverse their activity in accordance with the negative association of a particular food,” said Professor George Kemenes.
The study also found that when the neuron was completely removed from trained snails, they started eating sugar again.
“This suggests that the neuron is required for the expression of the learned behavior and for altering the response to sugar,” said Dr. Ildiko Kemenes.
‘However, we can’t rule out the possibility that the sugar-activated sensory pathway is also undergoing some changes, so we’re not going to assume that this is all that happens in the brain.’
The study is published in Current Biology.