News

Faulty brain brakes may drive addiction

Media Release, Tuesday 22 February 2005

Melbourne researchers have put forward a new theory of addiction that suggests a faulty braking mechanism in the brain may be to blame for the lack of control addicts seem to have, even when they know the consequences of their actions could be devastating.

The idea challenges a previously held belief of an over-responsive reward system as the sole root of addictive behaviour and has triggered an international debate on the causes, biology and treatment of addiction.

From the University of Melbourne’s Department of Psychiatry, ORYGEN Research Centre and the Melbourne Neuropsychiatry Centre, the researchers will now embark on a study to investigate their theory.

The study will be the first to use brain imaging to assess the role of both the reward and inhibitory systems in the brain in maintaining addictive behaviour in affected individuals.

Dr Murat Yücel says, “To date, few models of addiction have included the idea of a deficient stopping mechanism as a central feature. Rather, it is generally accepted that addiction is the result of a dysfunctional reward system that is overly activated by drugs or stimuli associated with drug use.”

The brain has an inbuilt reward system that releases dopamine and generates happy feelings after food, sex, water and nurturing behaviour. This circuit is a core feature of all animals and promotes survival and reproduction.

Dr Dan Lubman, another senior investigator on the project says drugs of abuse essentially work by hijacking this reward system, triggering it to release dopamine and positively reinforcing the desire for more drugs, such that drug use becomes more important than other activities.

“However, while the reward model explains the involuntary nature of craving and the motivational drive to continue using drugs, it does not explain why addicts are unable to control this drive when faced with potentially disastrous consequences,” he says.

Dr Yücel and his colleagues believe that dysfunction in areas of the brain known to be involved in the control and stopping of potentially dangerous or inappropriate behaviour could also be a core feature of addiction.

“Two areas of the brain known to be affected by long-term exposure to drugs of abuse – the orbitofrontal cortex (OFC) and the anterior cingulate cortex (ACC) – are also critically involved in assessing the future consequences of a person’s own actions and putting the brakes on inappropriate behaviours,” he says.

“We believe that this braking system is faulty in patients with compulsive behaviours like addiction, such that affected individuals cannot stop themselves even though they know the consequences of their actions could be devastating.”

The researchers hope that their brain imaging study will provide a better understanding of the brain regions and mechanisms associated with addictive behaviour.

Dr Lubman says, “Our hope is that a better understanding of these systems will help identify people who are vulnerable to addiction and aid in the development of early intervention strategies to reduce the addictive powers of drugs of abuse.”

The paper outlining the theory, along with debate and commentary from a number of international experts, was recently published in the journal Addiction, volume 99 (main article: pages 1491-1502; commentary: pages 1503-1507).

People interested in participating in this research (and who are currently on a maintenance program like methadone or buprenorphine OR people who have never had problematic drug and alcohol use or mental health problems) can contact Trudi Mackenzie (phone: 03 9342 2887; email trudi.mackenzie@mh.org.au) for more information.