Stress Makes Snails Forgetful

Scientists "train" the snails not to open their air-holes, or pneumostomes, by gently tapping them. Stressed-out snails don't learn from this training.
Scientists "train" the snails not to open their air-holes, or pneumostomes, by gently tapping them. Stressed-out snails don't learn from this training. (Image credit: Sarah Dalesman)

When humans are stressed out, they often have a tough time remembering things — and, it seems, the same goes for pond snails, according to a new study.

Researchers found that when pond snails are placed in an overcrowded pail or deprived of calcium, a mineral necessary for shell growth and reproduction, the "stressed-out" animals have trouble forming long-term memories, although their short-term recall remains intact. When the team combined the stressors, however, the snails' short-term memories fizzled, and they failed to form new memories, said Sarah Dalesman, a researcher at the University of Exeter in England.

"By combing the stressors, we can actually block all types of memory, and block learning, in which short-term memory is intimately involved," said Dalesman, co-author of the study, published Nov. 6 in the journal PLOS ONE. [7 Weird Ways Animals Act Like Humans]

The results suggest that stress can have additive effects on memory, which may also be the case in humans, since the same neural processes that underpin short- and long-term memory are similar in the two species, Dalesman told LiveScience.

To test the snails' memories, researchers first exposed the animals to stressful environments with low-calcium or overcrowding, or both. Next, the animals were placed in a pail with low levels of oxygen, mimicking the natural environment of swamps and slow-moving streams where the creatures live. In these types of environments, the snails can survive for more than two days by absorbing oxygen through their skin. They do, however, come to the surface to respire through their breathing hole, or pneumostome, Dalesman said. When the snails surfaced, the researchers tapped their pneumostomes, causing them to close.

After 30 minutes of this training, the snails were placed in a separate pail, and scientists then recorded how many times the snails came to the surface for air, testing their short-term memory of what would happen when they surfaced (their breathing holes would be closed). Snails that hadn't been stressed, or only subjected to one stressor, came up about three times less often than those exposed to multiple stressors, suggesting they learned from their "training session" and opted to make due with a low-oxygen environment. Snails that had been subject to overcrowding and calcium deficiency, however, came up the same number of times as before they were trained with the pneumostome poking.

The snails were then retrained, and again tapped for a half hour as they came to the surface. The scientists then tested the snails' intermediate- and long-term memories at 3 hours and 24 hours, respectively, by recording how often they came up for air. A single stressor impacted the snails' long-term memory but not their short-term memory, the study found.

In the study, calcium deficiency was meant to mimic physical stress, while the overcrowding served as a stand-in for psychological stress, making the results more relevant for mammals like humans, Dalesman said. However, there are limits to the parallels, as the brains of mammals like humans and those of snails are quite different, she added.

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Douglas Main
Douglas Main loves the weird and wonderful world of science, digging into amazing Planet Earth discoveries and wacky animal findings (from marsupials mating themselves to death to zombie worms to tear-drinking butterflies) for Live Science. Follow Doug on Google+.