A new study could reveal why some Parkinson’s patients develop harmful addictive behaviours.

Medicines that increase dopamine levels in the brain are the cornerstone of treatment for symptoms of Parkinson’s disease.

But experts say that while dopamine replacement therapy is effective for most people diagnosed with Parkinson’s disease, about one in six people treated with the medication develop impulse-control behaviours, such as gambling.

“We found people who developed these addictive behaviours differed in the way their brain structure interacted with dopamine-containing medication, which gave rise to the impulsive behaviour,” QIMR Berghofer Medical Research Institute lead researcher and St Andrews Hospital neuropsychiatrist Dr Phil Mosley said.

“None of these people had a history of addictive behaviours before diagnosis and only developed them after they began treatment with dopamine-replacement medications.

“There is currently no way of predicting which individuals are at risk of these terrible side-effects.”

More than 80,000 Australians are living with Parkinson’s disease, about 20 per cent of which are of working age, according to Parkinson’s Australia.

Dr Mosley said the study recruited 57 people with Parkinson’s disease from St Andrews War Memorial Hospital in Brisbane, in collaboration with neurologist Professor Peter Silburn.

“We used an advanced method of brain imaging, called diffusion MRI, to reconstruct the connections between different regions of the brain, akin to developing an individualised brain ‘wiring’ diagram for each person in the study,” Dr Mosley said.

“We asked our participants to gamble in a virtual casino, which gave us a readout of impulsive and risk-taking behaviour in real time.

“By combining data from brain imaging, behaviour in the virtual casino, and the effect of dopamine-replacement medication, we were able to identify people who were susceptible to impulse-control behaviours.

“More broadly, we found a clear link between the strength of the connections in the brain, within circuits that we think are crucial for making decisions and suppressing impulses, and impulsive behaviour, even in people without clinically-significant impulse-control behaviours.”

The findings indicate d that brain imaging and computer-based testing could be used in the future to determine which individuals are at risk of developing these harmful behaviours when treated with dopamine-replacement drugs.

The study is accessible here.