According to a new animal study, active choice may play an important role in resumption of cocaine use long after periods of abstinence, suggesting that the pharmacological effects of a drug alone may not be enough to explain the phenomena of addiction and relapse, ScienceDaily reported July 30.

Neuroscientists at the University of California, San Francisco's Ernest Gallo Clinic and Research Center have found that rats that voluntarily use cocaine show a persistent cellular memory in the brain after several months of abstinence, while involuntary users of the drug do not exhibit this cellular memory. The researchers believe this means that drug effects alone are not sufficient to generate these memories in the brain's reward circuit.

"We know that environmental cues are significant in many addictions, including tobacco and alcohol, and contribute to relapses," said Antonello Bonci, M.D., the study's senior author. "This study identifies the specific neuronal processes involved and helps explain relapse even after rehabilitative therapy or long-term abstinence."

The researchers also found that an increase in neuronal communication resulting from self-administered cocaine use lasted for up to three months after abstinence -- a significantly longer period than that for an increase in neuronal communication resulting from natural rewards such as food.

Study lead author Billy T. Chen, Ph.D., explained that these persistent potentiated synapses in rats could be the equivalent of several years of this activity for humans, confirming the notion that addiction is a lifelong disease with a high likelihood of relapse.

The study is published in the July 31 issue of the journal Neuron.