By Jeanene Swanson
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Can Blocking Memories Help Addicts Recover?
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There are, undoubtedly, many memories that addicts would love to forget. For most recovering addicts and alcoholics, encountering the so-called “people, places, and things” that remind them of using bring on the strongest cravings. Research has shown that repeated exposure to these cues—and then not getting to use—may temporarily ease cravings, but the association returns over time.
And, cravings equal relapse for the majority of addicts within the first year of sobriety. “Dealing with cravings is a major obstacle to recovery,” says Michael Saladin of the Medical University of South Carolina, “so it’s a natural target” for treating addiction. Saladin is one of a few clinical investigators who is looking at ways to interfere with cravings on the molecular level, such that these emotional memories can be erased.
As with most things in life—and addiction—there will be no easy fix.
Over the past several decades, science has slowly but surely upturned the entrenched idea of memory being relatively static—or, consolidated from “short-term” to “long-term” storage in the brain once and then left to deteriorate over the course of a lifetime. There is considerable evidence that memory can be interfered with during the initial consolidation period—both drugs that block protein synthesis in the brain and electroconvulsive shock can disrupt the formation of memories. It wasn’t until the late 1990s that researchers began really looking into the process of reconsolidation—what happens to memories when they are re-activated, or, recalled after they have been put into long-term storage.
In fact, recent research has found that memories are actually labile, in other words, open to being updated or changed during a short period of time after being recalled. A now-landmark study from 2000 out of Joseph LeDoux’s lab at NYU, and co-authored by Karim Nader, now at McGill University, found that they could erase fear memories in rats by injecting a chemical into their brains that stopped protein synthesis during a timeframe of about 6 hours after recall—they called this the “reconsolidation window,” and just like with new memories, reconsolidated memories require new proteins to be made. This reconsolidation window has most recently appeared on the radar of addiction treatment specialists as a way to interfere with—and possibly “erase”—craving memories.
There have been many studies looking at memory reconsolidation since 2000, but most have been done on rats. In all these studies it is important to understand the concept of fear extinction training. Harkening back to Pavlov’s classical conditioning studies, a neutral stimulus (say, a bell ringing) can be paired with a fearful stimulus (say, a shock to the rat’s foot) such that the rat learns to associate the neutral stimulus with the shock. After a while, the neutral stimulus alone will elicit a fear response. In fear extinction training, the subject is repeatedly exposed to the neutral stimulus—and continues to experience the fear without the actual shock—until the fear goes away. However, the extinction training can “wear off,” so to speak—this explains in part why addicts go back to using when they re-enter their old environments away from rehab, or simply, after a long enough period of time passes. Finding a way to interrupt memory reconsolidation in recovering addicts would go a long way toward preventing cravings and relapse.
Since drugs that block protein synthesis aren’t safe to use in humans, scientists have turned to drugs like propranolol (trade name Inderal), an FDA-approved beta-blocker that is already widely used to treat hypertension and stage fright. It works by lowering levels of the neurotransmitter norepinephrine, which, as it turns out, can also interfere with memory reconsolidation—norepinephrine is required for protein synthesis.
In the late 1990s, researchers at UC Irvine showed that propranolol could affect the emotional salience of a memory—while it can’t erase a memory, it can make it less emotionally relevant. The application of this work can be found in recent studies involving patients with PTSD—it might help victims of trauma dissociate their emotional memory from cues that remind them of what they went through, whether war-torn violence or domestic partner abuse. After decades of groundwork research, Harvard’s Roger Pitman found in a 2002 pilot study that exposing patients to propranolol immediately after a traumatic event might prevent them from developing PTSD.