Scientists know that addictive drugs can mess with the brain’s circuitry and hijack its reward systems, but a July 31 rat study in the journal Neuron shows that psychological factors may be more instrumental in causing these changes than a drug’s chemical effects are. Cocaine use triggers long-lasting cellular memories in the brain, the study found—but only if the user consumes the drug voluntarily.

A team led by Billy Chen and Antonello Bonci, both at the University of California, San Francisco, trained three groups of rats to press levers that delivered cocaine, food or sugar. The researchers injected cocaine into a fourth group. When they examined the rats’ brain tissue, they found an increase in synaptic strength within the reward center in those rats that had self-administered sugar, food or cocaine. These cellular memories were short-lived in the sugar and food groups, but in rats that had self-administered cocaine they persisted for up to three months after consumption had stopped. Most interestingly, the brains of rats that had consumed cocaine involuntarily did not show such imprints.

The findings illustrate that the pharmacological effects of cocaine alone are not enough to create reward-associated memories, Bonci says. “Instead the motivation for taking the drug seems to be a key component in the process as well.”

The team is working to find ways to remove the long-term cellular memory left by voluntary cocaine use, which eventually could help treat addiction in humans by taking away the desire to actively seek the drug, Chen says.

Note: This article was orignially printed with the title, "Hooked By Choice".

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