What's the News: Retrieving a memory in your brain is a bit like taking an old keepsake off the shelf. If you get startled while holding grandma's old vase in your hands, you could drop and break it. Memory retrieval is just as vulnerable to disruption, and scientists have tried to exploit this fact to erase PTSD-associated memories
with drugs. A new study in
tries a different tack, using a behavioral approach to rid people of addictions to drugs. Addiction is sometimes treated with "extinction," which means showing patients drug-related images while they're off drugs, so that, for example, they stop associating needles with a high. The researchers found that retrieving drug memories right before an extinction session---basically, giving them a short exposure to drug-related stimulus, followed by a similar but longer exposure session---made the treatment more effective in both rats and humans. How the Heck:
The researchers got rats addicted to either cocaine or morphine and gave them a short memory-retrieval session 10 minutes, one hour, or six hours before the longer extinction session. Memory retrieval was done by giving the rats a light and sound cue they had previously learned to associate with getting high. During the extinction session, the same cues were shown (and again with no drugs given), but for a longer time.
Rats who were reminded of drugs 10 minutes or one hour before extinction were less likely to use drugs again, either spontaneously or when presented with drugs. After six hours, however, the memory reconsolidation window had passed and those rats remained addicted.
To find a molecular signature, researchers looked at a protein called PMKzeta, which is associated with memory. In rats, extinction will change the expression of PMKzeta in different parts of the brain, and these changes were larger when memory retrieval came 10 minutes before extinction.
Human trials are the real heart of this study, since it's what works in rats doesn't always translate to humans. The researchers showed videos of neutral natural scenery and heroin use to heroin addicts, who were asked to rate their cravings induced by the videos.
Addicts who had the memory-retrieval session 10 minutes before their extinction session had lower cravings than those who had either no retrieval session or one six hours before extinction. This held true over a six-month period.
Fear of the Blue Square:
Using blue squares and mild electric shocks, a previous study had established proof of principal that disrupting memory retrieval can make extinction more effective. The experiment worked like this: participants were conditioned to associate a blue square with an electric shock, but if they were reminded of the blue square right before an extinction session, they learned more quickly to extinguish fear of the blue square.
The Future Holds:
The human subjects were all rehab patients confined to the hospital. Although the treatment dampened their reported cravings, there's no telling how much it will help when they return to the outside world and, for instance, run into their former dealers.
Nevertheless, the procedure is promising and, importantly, simpler and safer than chemical-based memory disruption for PTSD. The researchers will want to keep tabs on the treated patients as they leave the rehab clinic.
Reference: Yan-Xue Xue et al. A Memory-Retrieval-Extinction Procedure to Prevent Drug Craving and Relapse. Science 366, 241 (2012). DOI: 10.1126/science.1215070
Drug image via Shutterstock / buradaki
