Researchers have discovered a previously unknown pathway within the brain that links impulse with habits, which might explain why individuals have difficulty in controlling cocaine addiction, according to a study published Tuesday by the University of Cambridge.

Previous studies have shown that chronic exposure to drugs alters the prefrontal cortex in the brain, but it also alters an area of the brain called the basolateral amygdala, which is associated with the link between a stimulus and an emotion.

The basolateral amygdala stores the pleasurable memories associated with cocaine, but the prefrontal cortex manipulates this information, helping an individual to weigh up whether or not to take the drug: if an addicted individual takes the drug, this activates mechanisms in the dorsal striatum, which plays an important role in habitual behavior.

However, by studying the brains of rats addicted to cocaine through self-administration of the drug, researchers identified a pathway within the brain that links the basolateral amygdala indirectly with the dorsolateral striatum, circumventing the prefrontal cortex.

This means that an addicted individual would not necessarily be aware of their desire to take the drug, said the researchers.

"We've always assumed that addiction occurs through a failure of our self-control, but now we know this is not necessarily the case," said Dr. David Belin from the University of Cambridge, who is one of the authors of the study. "Drug addiction is mainly viewed as a psychiatric disorder, with treatments such as cognitive behavioral therapy focused on restoring the ability of the prefrontal cortex to control the otherwise maladaptive drug use."

"But we've shown that the prefrontal cortex is not always aware of what is happening, suggesting these treatments may not always be effective," said Belin.

In a second study, published in the journal Biological Psychiatry, Dr. Belin and colleagues showed that a drug used to treat paracetamol overdose may be able to help individuals addicted to cocaine overcome their addiction, provided the individual wants to quit.

The drug, N-acetylcysteine, had previously been shown in rat studies to prevent relapse. However, the drug later failed human clinical trials, though analysis suggested that while it did not lead addicted individuals to stop using cocaine, amongst those who were trying to abstain, it helped them refrain from taking the drug, according to the study.