Scientists at the Scripps Research Institute have managed to successfully isolate and remove memories from the brains of mice.
Eternal Sunshine of the Spotless Mind, anyone? In what has to be one of the more unkind experiments we've heard of scientists performing on mice, researchers at the Scripps Research Institute got a bunch of rodents addicted to methamphetamine, then successfully managed to erase the mnemonic associations that triggered drug cravings.
Here's why: addiction cravings are often triggered by specific behaviours. For cigarette addiction, for example, if the smoker becomes accustomed to having a cigarette with their morning cup of coffee, soon the act of having a cup of coffee will trigger an associated craving response. Likewise, meth addicts have reported craving associations with money, cigarettes and even chewing gum.
These associations, the Scripps Research Institute said, can push addicts trying to overcome their addiction back into it.
This is where the mice come in. If those associations could be erased from the addict's memory, overcoming the addiction would become significantly easier. The trick, of course, lies in removing just those memories, leaving the rest intact. And that is exactly what the Scripps team, led by TSRI assistant professor Courtney Miller, has managed to do.
"Our memories make us who we are, but some of these memories can make life very difficult," Miller said. "Not unlike in the movie Eternal Sunshine of the Spotless Mind, we're looking for strategies to selectively eliminate evidence of past experiences related to drug abuse or a traumatic event. Our study shows we can do just that in mice — wipe out deeply ingrained drug-related memories without harming other memories."
The team got its mice addicted to methamphetamine, then trained the mice to associate receipt of meth with a particular type of room. In a room that looked and smelled different to their usual habitats, the mice could self-administer methamphetamine by pressing a lever. When the mice were removed from, then returned to, the room, they would immediately start pressing the lever for a hit.
These memories are created with the help of a protein called actin, which alters the structure of nerve cells via the brain's dendritic spines — the structures that receive signals from other neurons.
It's this protein that the scientists targeted. They injected the mice with a medication that inhibits actin from creating chain-like molecules by blocking molecular motor myosin II. When the mice were returned to the meth room, they no longer had any interest in pressing the lever, suggesting that the association had been removed from their memories.
Memories associated with food shock or food reward, however, were not affected.
The scientists are unsure why the meth-related memories were so fragile — but the fact that it works at all, they believe, suggests a relation to dopamine, the neurotransmitter associated with the brain's reward and pleasure centres.
"We are focused on understanding what makes these memories different," Miller said. "The hope is that our strategies may be applicable to other harmful memories, such as those that perpetuate smoking or PTSD."
You can read the full paper, "Selective, Retrieval-Independent Disruption of Methamphetamine-Associated Memory by Actin Depolymerization", in journal Biological Psychiatry.