Friday, September 13, 2013

Selectively erasing unwanted memories

September 13, 2013
Jim Carrey in  Eternal Sunshine of the Spotless Mind (credit: Universal Studios)
Scientists from the Florida campus of The Scripps Research Institute (TSRI) have been able to erase dangerous drug-associated memories in mice and rats without affecting other more benign memories.
The surprising discovery points to a clear and workable method to disrupt unwanted memories while leaving the rest intact, the scientists say.
For recovering addicts and individuals suffering from post-traumatic stress disorder (PTSD), unwanted memories can be devastating. Former meth addicts, for instance, report intense drug cravings triggered by associations with cigarettes, money, even gum (used to relieve dry mouth), pushing them back into the addiction they so desperately want to leave.
As in the movie Eternal Sunshine of the Spotless Mind (a couple undergo a procedure to erase each other from their memories when their relationship turns sour), “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,” said Courtney Miller, a TSRI assistant professor who led the research.
How to change memories
  1. Mice and rats were first trained to associate the rewarding effects of methamphetamine with a rich context of visual, tactile and scent cues.
  2. The scientists later inhibited actin polymerization — the creation of large chainlike molecules — by blocking a molecular motor called myosin II in their brains during the maintenance phase of methamphetamine-related memory formation. (To produce a memory, a lot has to happen, including the alteration of the structure of nerve cells via changes in the dendritic spines — small bulb-like structures that receive electrochemical signals from other neurons. Normally, these structural changes occur via actin, the protein that makes up the infrastructure of all cells.)
  3. Behavioral tests showed the animals immediately and persistently lost memories associated with methamphetamine. At the same time, the response to other memories, such as food rewards, was unaffected.
The scientists are not yet sure why powerful methamphetamine-related memories are also so fragile, but they think it could be related to the role of dopamine, a neurotransmitter involved in reward and pleasure centers in the brain. Dopamine is released during both learning and drug withdrawal.
“The hope is that our strategies may be applicable to other harmful memories, such as those that perpetuate smoking or PTSD,” Miller said.
The research was supported by the National Institute on Drug Abuse and the National Institute for Neurological Disorders and Stroke.


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