The tiny foragers are also “excellent learners,” Crossley said, remembering things after a single encounter. In the new study, researchers looked deep into the snails’ brains to figure out what’s going on neurally when they acquire memories.
stir up memories
In the experiments, the researchers trained the snails in two forms: strong training and weak training. During the intense training session, they first sprayed the snails with banana-flavored water, which the snails perceived as neutral: They swallowed some, then spit some out. The team then fed the snails sugar, which the snails gorged themselves on.
When they tested the snails a day later, the snails showed that they had learned to associate the taste of bananas with sugar from that experience. The snails seem to find the taste more desirable: They prefer to swallow water.
In contrast, the snails did not learn this positive association from weak training in which they were given a coconut-flavored bath before eating much diluted sugar. The snail continues to swallow and spit out water.
So far, the experiment is essentially a snail’s version of Pavlov’s famous conditioning experiment, in which dogs learned to salivate when they heard a bell. But then, the scientists looked at what happened when they intensely trained the snails with a banana flavoring and then weakly with a coconut flavoring a few hours later. Suddenly, the snail also learned from weak training.
When the researchers changed the order and trained weakly first, it again failed to transfer the memory. The snails still formed memories of the reinforcement training, but this did not have the effect of retroactively reinforcing previous experiences. Swapping the flavors used in strong and weak training also had no effect.
The scientists concluded that intense training pushed the snails into a period of “learning richness,” during which the threshold for memory formation is low, allowing them to learn things they would not otherwise learn (such as the difference between flavors and flavors). weak training association between them). diluted sugar). This mechanism helps the brain direct resources to learning at the appropriate time. Food can make snails more alert to potential food sources nearby; brushing past danger increases their sensitivity to threats.
A Vertebral A snail that associates flavored water with sugar quickly opens and closes its mouth to swallow it (right). A snail that has not learned to associate with its mouth closed (left).Video: Michael Crossley, Kevin Staras/Quanta Magazine
However, the effect on the snails was short-lived. The learning-enrichment period after intense training lasted only 30 minutes to 4 hours. Afterwards, the snails stopped forming long-term memories during weak training, not because they forgot the strong training—the memory persisted for several months.
Establishing a critical window for reinforcement learning makes sense, because if the process isn’t shut down, “it could be detrimental to the animal,” Crossley said. Not only may animals invest too much resources in learning, but they may learn associations that are detrimental to their survival.
concept change
Using electrode probing, the researchers discovered what happens inside the snail’s brain as it forms long-term memories during training. Two parallel adjustments in brain activity occurred. The first encodes the memory itself. The second “purely involves changing the animal’s perception of other events,” Crossley said. It “changes the way it sees the world based on past experience.”
They also found that the same shift in snail perception could be induced by blocking the effects of dopamine, a brain chemical produced by neurons that activate the behavior of spitting. In effect, this turns off the spit neurons and keeps the swallow neurons turned on. The experience had the same carry-over effect as the strong training in the previous experiment: After a few hours, the snails formed long-term memories of the weak training.
