In the film Eternal Sunshine of the Spotless Mind
, Jim Carrey played a man who had his brain scrubbed of painful memories - only to have them eventually come back to haunt him.
While the selective deletion of memories may sound like science fiction, neuroscientists from The Scripps Research Institute have demonstrated just that in mice and rats, according to their report in the journal Biological Psychiatry
The Scripps researchers said the technique might be useful for treating people suffering from post-traumatic stress disorder (PTSD) or battling a drug addiction.
"Our memories make us who we are, but some of these memories can make life very difficult," said study leader Courtney Miller
, a TSRI assistant professor of neuroscience. "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 engrained drug-related memories without harming other memories."
When a memory is created, changes occur to the structure of dendritic spines found on nerve cells. These small, bulb-like structures receive electrochemical transmissions from other neuronsn and structural changes to them normally occur via a protein called actin.
In the new study, the scientists inhibited actin polymerization, a process that results in the creation of large, chainlike molecules. By blocking a molecule called myosin II in mouse and rat brains during the maintenance phase of methamphetamine-associated memory formation, the Scripps scientists were able to disrupt the polymerization process.
Behavioral experiments showed the rodents immediately and reliably lost memories connected with methamphetamine - with no evidence of other memories being affected.
In the experiments, the rodents were trained to relate the 'rewarding' sensations of methamphetamine use with a range of strong visual, tactile and scent cues. When they were given the polymerization inhibitor many days later in their same environment, the test subjects demonstrated a complete lack of interest when they were later given drug-associated cues. The subjects' response to other memories - like food rewards - was unaffected, researchers said.
While the neuroscientists said they aren't sure why these powerful methamphetamine-related memories are also so delicate, they theorized that the findings could be linked to the role of dopamine, a reward- and pleasure-associated neurotransmitter also known to modify dendritic spines. Previous research has shown dopamine is released during both learning and drug withdrawal.
"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."
An effective treatment for PTSD would come as welcome news to the approximately 7.7 million American who have been diagnosed with the condition. While women are more likely to be diagnosed with PTSD than men, there is some data that suggests susceptibility to the condition may run in families, according to the National Institutes of Health
PTSD can affect a person at any age, and may include war veterans, survivors of sexual assault, disasters, and other serious events.