Tiny foragers are also “remarkable learners” who can remember something after being exposed to it, Crossley said. In the new study, researchers looked deep into the brains of snails to find out what happened at the neural level when they acquired memories.
Memories
In their experiments, the researchers gave snails two forms of training: strong and weak. During intense training, they first sprayed the snails with banana-flavored water, which the snail considers neutral in its attractiveness: They swallow some but then spit some out. . The team then gave the snails sugar and they devoured them.
When they tested the snails a day later, the snails showed that they had learned to associate banana flavor with sugar from that single experience. The snails seemed to find that taste more appealing: They were much more willing to swallow the water.
In contrast, the snails did not learn this positive association from a weak training session in which a coconut-flavored bath was followed by a much thinner sugar. The snails continued to swallow and spit out water.
So far, the experiment is essentially a snail version of Pavlov’s famous conditioning experiment, in which dogs learn to drool when they hear a bell. But then, the scientists looked at what happened when they trained the snails vigorously with banana flavoring, followed by a few hours later with weak training with coconut flavoring. Suddenly, the snails also learned from poor training.
When the researchers changed the order and performed the weak training first, it failed to transmit the memory again. The snails still formed strong training memories, but that had no retroactive reinforcement of previous experience. Swapping the flavors used in the strong and weak trainings doesn’t work either.
The scientists concluded that intense training pushed the snails into a “high-learner” stage, in which the threshold for memory formation was lower, allowing them to learn things they didn’t (such as such as weakly trained association between flavor and sugar dilution). Such a mechanism could help the brain direct resources to learning at the right times. Food can make snails more alert to potential food sources nearby; Brush with danger can enhance their sensitivity to threats.
ONE Lymnaea snails that bind flavored water with sugar quickly open and close their mouths to swallow it (right). A snail that doesn’t know that association closes its mouth (left).Video: Michael Crossley, Kevin Staras/Quanta Magazine
The effect on snails, however, was transient. The rich learning phase lasts only 30 minutes to four hours after intense training. The snails then stopped forming long-term memories during weak training, and it wasn’t because they had forgotten their intense training—the memory of that persisted for months.
Having a critical period for advanced learning makes sense, says Crossley, because if the process isn’t turned off, “it could be detrimental to the animals.” Then the animal may not only invest too many resources in learning, but may also learn associations that are harmful to its survival.
Changing perception
By probing with electrodes, the researchers found out what happens inside the snail’s brain as it forms long-term memories from training sessions. Two parallel adjustments in brain activity occur. The first one encrypts the memory itself. The second is “entirely related to altering the animal’s perception of other events,” says Crossley. It “changes the way it sees the world based on its past experiences.”
They also found that they were able to induce a similar change in snail cognition by blocking the effects of dopamine, the brain chemical produced by neurons that trigger spitting behavior. . In fact, that causes the neuron in charge to release and causes the neuron in charge of swallowing to continuously work. This experience had the same transference effect as vigorous training did in previous experiments: A few hours later, the snails formed a long-term memory of the weak training.
