Why are scientists getting pond snails hooked on meth? To figure out how addiction works. But they discovered something else: Meth enhances memory. What you learn when high stays with you longer and more clearly than what you learn sober.
Lymnaea stagnalis — better known as pond snails — are widely used to study learning and memory due to the fact they only have around 20,000 neurons, many of which are individually identifiable. Amphetamines affect memory, making the drug especially difficult to leave behind. By using an organism with a well-understood brain, scientists thought they might be able to better understand the effect crystal meth has on the memory and the mind.
So how do you see what happens with the memory of a snail? Lymnaea stagnalis has a very defined limit to learning — if you give it two training sessions separated by an hour, it'll retain the lesson for 24 hours. To train the molluscs, researchers placed them in de-oxygenated water with methamphetamine added, and poked the snails whenever they tried to reach their breathing tubes above the water to boost their oxygen intake. This negative reinforcement taught them not to stick their pneumostomes, or snail noses, above water.
Not only did the pond snails trained in meth water remember their task far longer than those trained in normal water, but once they were in a non-methamphetamine environment, if the drug was added to the liquid again, they would suddenly recall their training. Attempts to retrain them without drugs proved to be difficult, as memories formed while on the drug were far more resilient than those off of it.
What does this mean for humans? Memories formed while high on methamphetamine are particularly intense. Couple the intense rush and euphoria the drug provides with an inability to forget how it felt, and you can see how this would make quitting even harder. Revisiting the places of addiction is also thought to trigger these memories, which is why many recovering addicts are advised to avoid their old haunts.
It's still not clear why methamphetamine memories are so resilient, but one possible reason is that the drug may disrupt the mechanism that allows us to forget.
Read the full paper, published in The Journal of Experimental Biology