Drug-users have difficulty changing their habits because drugs alter certain areas of the brain, writes Vikki Burns
Drug-users may have an impaired ability to detect errors in their behaviour and to correct them in the future, according to a scientist from Trinity College Dublin. This could leave campaigns to "Just Say No" ineffective in treating drug use.
"A hallmark of drug abuse is the persistence of drug-taking behaviour despite repeatedly adverse outcomes on physical and social well-being," says Dr Hugh Garavan, senior lecturer in psychology and director of functional imaging at Trinity College Institute of Neuroscience, Dublin.
Garavan participated in a session entitled A Window Into the Brain at last week's BA Festival of Science.
"Our research shows that drug-users may have poorer psychological control over their behaviour, including detecting and correcting mistakes," he told Science Today.
His collaborator, Dr Julie Stout, used a laboratory gambling task to compare the cognitive, or psychological, dimension of behavioural control in drug-users and non-users.
"In the gambling tasks, some of the decks of cards are more rewarding than others in terms of the likelihood of winning," Garavan says.
After each choice that the volunteers made in the task, they were given feedback about how successful their decision had been to help them work out which of the decks was rewarding.
"The drug-users were less able to correct their future behaviour, based on these errors, even when this explicit feedback was given," explains Garavan.
The activity of the brains of drug- users can also provide an insight into their behavioural control, according to Garavan. He used functional Magnetic Resonance Imaging (fMRI) to compare the brain activity of drug-users and non-users during these tasks.
"Standard MRI machines in hospitals produce pictures of bone and soft tissue, whereas fMRI machines measure blood flow," says Garavan. "The more neural activity in a particular area of the brain, the greater the blood-flow. This allows us to measure the extent of activation of different areas of the brain during different tasks."
The volunteers had their brains scanned using the fMRI while they performed similar cognitive tasks.
"During the tasks, drug-users showed less activity in the anterior cingulate cortex," says Garavan. "This area of the brain is associated with behaviour inhibition and error detection. Even when motivation to perform well was enhanced by financial reward, activation in these areas remained low in drug- users."
This suggests that the observed differences between drug-users and non-users were genuine differences in behavioural control, rather than being caused by differences in how motivated they were to perform the task.
"This impairment is likely to compromise their ability to monitor their own behaviour," Garavan says. "If their behaviour is less under their own control, then it is more likely to be guided by environmental cues or their habits. This may be why they continue to use drugs repeatedly."
A key question is whether these differences precede drug use or are a consequence of it.
"There is evidence from animal studies that drugs can cause cognitive deficits," says Garavan. "However, there are also studies that show that measures of impulsive behaviours at age 12 predict drug use at 19. It is likely to be a combination of these factors. We would like to find out if differences in cognitive processes explain the hereditary nature of addiction, and the question of why only some users become addicts."
This research is "adding an important piece to the conceptual puzzle that must be solved to understand, treat, and prevent drug abuse", according to Garavan.
"It may be possible in future to design behavioural interventions to help users practice monitoring and inhibiting their behaviour, or even to develop tailored pharmacological treatments," he believes.