It’s a nauseous feeling we can all relate to; one bad food experience makes it difficult to stomach the idea of eating that particular dish ever again – regardless of how much you enjoyed it before the unfortunate incident.
Maybe it was an undercooked cheeseburger that led to food poisoning or a platter of sushi that just didn’t agree with you. Experiences like these make the notion of another cheeseburger or California roll in the future sound about as desirable as a trip to the DMV. Once our minds seem to establish the connection between a particular item of food and intestinal distress, it can take a long, long time to get over that.
Now, a fascinating new study from the University of Sussex has unlocked some of the neurological machinations behind this universal human tendency. Thanks to some help from a group of sugar-loving snails, researchers have discovered that negative food experiences appear to flip a switch in the mind, subsequently changing one’s eating habits moving forward.
Just like many humans, snails love sugar. So, predictably, if you put some sugar in front of a snail they’re going to start eating some. This is exactly what researchers did for a group of lab snails, but gradually over time they started gently tapping the snails on the head whenever sugar was placed in front of them.
This eventually created a negative association for the snails (sugar equals a tap on the head). Once this association had been established, the snails stopped eating any readily available sugar, even if they were quite hungry.
A more comprehensive analysis of the snails’ brains showed the research team that the very neuron responsible for suppressing hunger and ensuring that snails don’t eat anything and everything “learns” not to shut off in response to sugar. Normally, this neuron would switch itself off whenever some appealing food is within grasp.
“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,” explains study leader Dr. Ildiko Kemenes, Reader in Neuroscience in the University of Sussex’s School of Life Sciences, in a release.
“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,” she continues.
It may be hard to believe considering their tiny stature, but snail and human brains are actually quite similar. Study authors say these findings likely apply to human eating tendencies as well.
“Snails provide us with a similar yet exceptionally basic model of how human brains work,” says senior investigator George Kemenes, Professor of Neuroscience at the University of Sussex. “The effect of the inhibitory neuron which suppresses the feeding circuit in the snail is quite similar to how, in the human brain, cortical networks are under inhibitory control to avoid ‘runaway’ activation which may lead to overeating resulting in obesity.”
Importantly, when the sugar was replaced with another food, the snails wasted no time eating their meal. This just confirmed that the negative association only pertained to one food item, just as it would in humans.
“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,” Professor Kemenes comments. “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.”
Researchers even took the study a step further and removed the neuron completely from the snails’ brains. Sure enough, after this took place the snails went right back to their sugar-eating habit.
“This suggests that the neuron is necessary for the expression of the learned behavior and for altering the response to sugar,” Dr. Kemenes concludes. “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.”
In summation, these findings are yet another illustration of how our brains never stop learning and changing in pursuit of one goal: to protect us. It may not be particularly fair to consider all burritos bad news after just one negative experience, but our brains are just trying to look out for our stomachs.
The full study can be found here, published in Current Biology.