In the film Eternal Sunshine of the Spotless Mind, Jim Carrey's and Kate Winslet's characters have their painful relationship memories erased. Now, researchers have demonstrated a method in mice that disrupts unwanted memories while leaving the rest untouched.
Though it may sound like science fiction, the results, which were published in the journal Biological Psychiatry, are very real.
The team, led by Courtney Miller from The Scripps Research Institute (TSRI) in Florida, successfully erased drug-associated memories in mice and rats, providing hope for recovering addicts or people suffering from post-traumatic stress disorder (PTSD).
They note that former methamphetamine addicts have reported drug cravings triggered by memory associations. Money, cigarettes and even gum can pull them back to the addiction they tried so hard to leave behind.
Memories are quite complicated to produce, says the team. Changes in the dendritic spines - small structures that receive signals from other neurons - have to happen, altering the structure of nerve cells in the process.
Actin, a protein that makes up the structure of cells, normally plays a role in this process.
But in the mice and rats, the researchers inhibited actin polymerization - which they say is the creation of large "chainlike" molecules - by blocking a "molecular motor" called myosin II.
They did this during the "maintenance phase" of methamphetamine-related memory formation.
Courtney Miller, who is a TSRI assistant professor, explained to Medical News Today that the maintenance phase "refers to the long period that a memory sits in storage, after being formed, waiting to be retrieved."
She explained that they are excited about their findings because their manipulation "disrupts the memory long after it has formed."
Tests conducted after the manipulation revealed that the mice and rats "immediately and persistently" lost all memories associated with methamphetamine. All the other memories, such as food rewards or foot shock, were still intact.
"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 engrained drug-related memories without harming other memories."
Understanding powerful, yet fragile memories
During the tests, the animals were trained to link the satisfying effects of methamphetamine with visual, tactile and scent cues. But when the researchers injected them with the inhibitor several days later, they showed a total lack of interest in drug-related cues.
The scientists say they do not yet know why methamphetamine-related memories are so "fragile," but they think it could have something to do with dopamine, which is a neurotransmitter that plays a role in the reward and pleasure areas of the brain.
Dopamine is also known to modify dendritic spines, they say, and they add that drug-associated memories seem to be maintained by a particular form of actin that is driven by myosin II.
"We are focused on understanding what makes these memories different," says Miller. "The hope is that our strategies may be applicable to other harmful memories, such as those that perpetuate smoking or PTSD."
Miller told Medical News Today why their findings are so unique:
"We maintain selectivity for the drug-associated memory without having to retrieve it. That's valuable because substance abusers develop many, many associations with the drug, so it may not be practical to ask them to retrieve every single association in the clinic.
In our case, the manipulation can occur at any time and, apparently, only erase the drug-associated memories."
Though we may not be able to expunge past relationships from our memory, like in Eternal Sunshine of the Spotless Mind, sufferers of drug addiction and PTSD could one day gain some relief in the form of forgetting.