A UNIVERSITY professor has made a trailblazing discovery with the help of gin and tonic, pear drops, and pond snails.

After a decade studying snails, Dr Michael Crossley believes he may have glimpsed the reason we find it hard to remember multiple similar things at the same time.

The research, published last week, reveals why snails struggle to learn when they are bombarded with information.

The study is based on previous findings that show bad memories stay with snails for weeks.

Dr Crossley, of Sussex University, said: “The way I think about it is if you go to a restaurant once and get sick after, you’re always going to associate that restaurant with being ill.

“But if you’re being introduced to a big group of people, you probably won’t remember all their names.”

The reason for this in snails, the study showed, is they store similar memories in the same place — and only seem to have room for one.

Like humans, snails record the lessons they have learnt in neurones, cable-like cells that club together to transmit signals from the brain to the rest of the body.

Dr Crossley said: “The snails use the same mechanism as us, but where humans have got billions of neurones, they only have about 30,000. They’re much easier to test.”

The experiment involved attaching electrodes to different neurones in the snails’ brains.

It also made use of an assortment of flavours, including coconut, pear drop and quinine – the ingredient that gives tonic water its bitter taste – which snails hate.

“They’re not on board with the gin and tonic craze,” said Dr Crossley.

“That gave us a way to test that restaurant analogy. In these experiments, what we do is a bit like Pavlov’s famous study, where a dog learns to expect food when it hears the sound of a bell.

“It’s just there’s no bell, instead, we use flavours. And instead of dog food, we’re using sugar. Snails love sugar.”

The experiments took place in a petri dish containing the aquatic snails lymnaea stagnalis. About the size of a grape, the gastropods are found in almost any pond in the northern hemisphere.

The researchers showed snails can remember a single lesson such as “pear drop scent means food” after just two minutes of training.

Dr Crossley said: “We found they could recall a lesson like that the next day. And then we found they can still remember three weeks later.

“We already had an idea that snails have a pretty good memory. But that’s in an artificial setting where we test just one lesson. In real life, you’re confronted with lots of experiences that interfere with how much you remember.

“We wanted to understand the rules behind how they interfere so we added another lesson. We trained them to expect the same reward but with a different flavour, like coconut. But they seemed to get pretty confused.

“The important bit was when we looked at the neurones. If the snail’s learning a like and a dislike, it can remember them both — the memories are kept in different places.

“But if it’s two similar things, they’re both vying for space in the same neurone. That, we think, is why they can’t keep track of what they’ve learnt.”

It has taken Dr Crossley years to arrive at this conclusion. But it’s a lesson unlikely to be forgotten in a hurry.

He said: “This is the first time someone’s done this at this level of detail.

“It has important implications for understanding our own memory, and why it is we forget.”