Old Memories Can Prime Brains to Make New Ones

The tiny collectors are also “remarkable learners” who can remember something after a single exposure, Crossley said. In the new study, the researchers looked deep into the snails’ brains to find out what was happening at the neurological level as they collected memories.

bring back memories

In their experiments, the researchers gave the snails two forms of training: strong and weak. During the heavy training, they first sprayed the snails with banana-flavored water, the effect of which was considered neutral by the snails: they swallowed some of it, but then spat it out again. Then the team gave the snails sugar, which they devoured greedily.

When they tested the snails again a day later, the snails showed that they had learned to associate the banana flavor with the sugar from that single experience. The snails seemed to find the taste more desirable: they were much more willing to swallow the water.

In contrast, the snails did not learn this positive association from a light training session in which a coconut-flavored bath was followed by a much more diluted sugar treat. The snails swallowed and continued to spit out water.

So far, the experiment has essentially been a slug version of Pavlov’s famous conditioning experiments, in which dogs learned to drool when they heard the sound of a bell. But then the scientists looked at what happened when they gave the snails a heavy banana-flavored workout followed by a light coconut-flavored workout hours later. Suddenly the snails learned from the weak training.

When the researchers changed the order and did the weak training first, they again failed to induce memory. The snails still formed a reminder of the heavy training, but it had no retroactive reinforcing effect on the earlier experience. Swapping the flavors in the strong and weak workouts also had no effect.

The scientists concluded that the heavy training put the snails in a “busy” phase, where the threshold for memory formation was lower, allowing them to learn things they otherwise could not have learned (e.g., .the weak training association between a flavor and…). dilute sugar). Such a mechanism could help the brain direct resources to learning at the right time. Food might increase the snails’ awareness of potential nearby food sources; Touches of danger could heighten their sensitivity to threats.

However, the effect on the snails was only temporary. The learning phase lasted only 30 minutes to four hours after the strong training. After that, the snails stopped forming long-term memories during the light workout, and it wasn’t because they forgot their heavy workout—the memory of it lingered for months.

A critical window for enhanced learning makes sense because if the process wasn’t shut down, “it could be harmful to the animal,” Crossley said. Not only could the animal then invest too many resources in learning, but it could also learn associations that are detrimental to its survival.

Altered Perceptions

Using probes with electrodes, the researchers found out what happens in a snail’s brain when it forms long-term memories from the training sessions. Two parallel changes in brain activity occur. The first encodes the memory itself. The second is “solely about changing the animal’s perception of other events,” Crossley said. It “changes the way they see the world because of their past experiences.”

They also found that they could induce the same change in the snails’ perception by blocking the effects of dopamine, the brain chemical produced by the neuron that activates spitting behavior. In fact, this turned off the spitting neuron and kept the swallowing neuron on all the time. The experience had the same carryover effect as heavy training in the previous experiments: Hours later, the snails formed a long-term memory of the light training.