Snails Confirm An Old Trick To Store More Memories Really Works

The freshwater pond snail Lymnaea stagnalis has given us an opportunity to confirm something that seems to be the case, but is much less clear, in humans. Vitalii Hulai/Shutterstock

If you want people to remember you, marketing courses teach: be first in a new field, not second or third in an established one. Snails have much more limited memories than us, but the same principle holds.

Dr Michael Crossley of the University of Sussex set out to see how much he could teach pond snails. It may seem an unusual ambition, but Crossley explained in a statement: "The brain of a snail is much simpler than ours but there are some key parallels, which mean studying them can help us to understand more about our own abilities for learning and memory.” It's also probably a relief to have test subjects with limited escape potential.

When Crossley tried to teach his charges two things in succession he found they could remember both if they were unrelated. However, when the two items were similar, the snails couldn't manage to hold both in their slimy little heads.

In Communications Biology, Crossley explains that similar memories were overwritten on a single neuron, which could not hold both. Different topics were filed with different neurons.

Of course humans, or snails, can eventually learn to remember multiple closely related facts, or Latin declensions would be even more hellish than they are. To achieve this, timing is as important as topic. We store what we learn initially in short-term memory, and subsequently consolidate those parts that seem important in long-term memory. Crossley's challenged his snails with new facts before they'd consolidated the old one, something he compares to being introduced to several people at once and struggling to remember all their names.

Crossley gave his snails their second lesson either one, two, or 24 hours after the first. An hour after learning something snails still have it in their short-term memory. A day later it has been shifted to long-term, but two hours falls into a “memory lapse” period where the information is in the process of being shuttled between.

If the lessons were different, timing didn't matter – both stuck. When they were too similar, however, it was the first one that held when they came close together, but delivery during the lapse saw the second one override the first. After a day the snails had consolidated the first memory and were ready to learn more.

If you're curious to know what counts as similar and dissimilar lessons for a snail, Crossley either taught them to associate chemicals with a sugar reward, or with bitter tasting quinine.

Although more profound lessons about the nature of learning may eventually emerge from this work, Crossley points to an immediate example of advice snails can offer. He suggests students studying for exams should switch back and forwards between their subjects, rather than saturating on any particular topic.

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