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Deleting memories to cure addiction

1-29-2019

Courtney Heinnickel, Contributing Writer

New research shows that disrupting memories that associated environmental cues with

drug use significantly reduces drug-seeking behaviors in rats. This recent discovery was made at

the University of Pittsburgh School of Medicine and opened a potential avenue for developing

more effective therapies to prevent relapse. Ever since the discovery of classical conditioning in

dogs made by Pavlov in the 1890s, it has been recognized that the brain associates specific cues

with behaviors, like the smell of freshly made cookies making you want a batch. Breaking the

links between cues and memories is a well-known strategy in treating phobias, addiction, and

PTSD. However, this method, commonly known as ‘exposure therapy, is not very effective at

treating addiction. This is because of the uncontrolled setting in which a person is released into

after treatment. In a controlled setting such as a doctor’s office, the person may be fine and able

to forget about the addiction, but once released into the outside world, the brain reverts back into

this drug-seeking phase.

In the study used at the university, scientists used a rat model of cue-associated relapse.

When the rats pressed a lever, they received an infusion of cocaine, accompanied by a tone and a

light. Eventually, the rats learned to associate the audiovisual cue with the cocaine high, and

showed a drug-seeking behavior and craving and repeatedly pressed the lever. The second

experiment tested exposure therapy in rats. This included showing the rats the same light as

before along with the tone, but not providing the cocaine. The results showed that the rats began

to show less of the drug-seeking behavior. However, like humans, when the exposed rats were

placed in a different environment, they began to show the drug-seeking behavior again.

Then, using electrical recordings from rat brain tissue, the researchers showed that

connections between the medial geniculate nucleus, the brain’s switchboard for sound, and the

lateral amygdala is important for forming memories that associate the cocaine high with

external cues. The researchers then used a technique known as optogenetics, where light pulses

are used to control genetically modified cells, to control the neurons from the previous

experiment. Rats that have the cocaine-cue memories optogenetically erased pressed the lever

significantly fewer times when the light and tone cue was played. The reduced relapse behavior

persisted even when the rats were placed in a different environment, suggesting that eliminating

cue-associated memories overcome the relapse-inducing effects of a new environment.

Mary Torregrossa, Ph.D., associate professor of psychiatry at Pitt’s School of Medicine and senior author of the study said, "In the long term, these findings may help us develop drugs or

approaches like deep brain stimulation to specifically target these memories strengthened by

substance use and improve the success of exposure therapy to prevent relapse." This new

research could lead to many new ways to cure drug addiction in different patients and change the

lives of many around the world.