Australian researchers have found a way to make a potentially "life-changing" brain stimulation treatment for Parkinson's disease more effective and safer.
Researchers at QMIR Berghofer Medical Research Institute identified ways to reduce the harmful side effects of one of the most widely-used advanced treatment for Parkinson's disease - deep brain stimulation therapy.
Deep brain stimulation (DBS) involves implanting electrodes in the brain, to target small regions of the brain with electrical currents. The neurosurgical procedure has been shown to reverse some motor-related symptoms of Parkinson's disease, including tremor, stiffness and slowness, with some patients even able to stop medication.
QIMR Berghofer lead researcher and St Andrews War Memorial Hospital neuropsychiatrist, Dr Philip Mosley, said the procedure was being used more frequently for the treatment of Parkinson's disease because it reduces disability and improves quality of life for several years, but it can also have harmful side-effects.
"Some patients develop new problems with controlling their impulses and behaving recklessly after this procedure, which can give rise to personal problems and increase the strain on their families," Dr Mosley said.
As well as a small proportion of Parkinson's patients who undergo DBS reporting impulsive and reckless behaviour post procedure, some develop harmful behaviours such as gambling, binge eating, hypersexuality and/or excessive shopping.
"We identified that when DBS affected certain parts of the brain, it was linked to impulsivity and harmful behaviour."
He said knowing which connections were harmful or helpful would assist neurologists and neurosurgeons decide where best to place the DBS electrodes and how to adjust the device postoperatively so that only regions of the brain responsible for treating the motor symptoms of Parkinson's disease were stimulated.
"These impulse-control and behavioural problems limit the improvement in quality of life enjoyed by the majority of patients who undergo this procedure.
"We wanted to find out if there was a subtle difference in the way stimulation was affecting the brains of those people who developed these psychiatric side-effects, and if by exploring these differences we might be able to work out how to stop it happening altogether."
Dr Mosley recruited 55 recent patients into the study and used an advanced method of brain imaging, called diffusion MRI, to reconstruct the connections between nerve cells in the brain that were stimulated by the implanted electrodes.
"We used a 'virtual casino' that we had previously developed, which simulated 'real-world' impulsivity, and looked at how the brain networks influenced by DBS affected gambling." said Dr Mosley.
"Our participants played the casino before DBS and again once their stimulator was implanted and turned on, so we could quantify whether stimulation influenced them to bet in a more risky manner."
Dr Mosley found that when stimulation affected the frontal portion of the brain (the prefrontal cortex), participants were more likely to place higher, more risky bets after DBS.
"This region of the brain is important for planning behaviour and inhibiting inappropriate actions, so it makes sense that stimulation of this part of the brain can change behaviour in this way," he said.
Dr Mosley also followed the clinical progress of all participants in the study and found that those patients who went on to develop clinically-significant, harmful changes in behaviour after DBS had a strong connection between the site of stimulation and a specific region of the prefrontal cortex called the orbitofrontal cortex.
"This was a fascinating finding, because this region has been shown to be important in how the brain evaluates a desired goal and compares it to an actual outcome, in order to work out if behaviour should be modified," he said.
"It is possible that these individuals developed such significant problems because their brains weren't able to perform this function, which meant that they didn't link poor choices to negative outcomes, and therefore didn't learn from the experience."
"Overall, DBS for Parkinson's disease is usually a wonderful and life-changing treatment. Now, our understanding of how behaviour can be linked to the pattern of connections in the brain stimulated by DBS means that we can make this therapy even safer and more effective.
"Specifically, knowing which connections are harmful or helpful will assist neurologists and neurosurgeons decide where best to place the DBS electrodes and how to adjust the device postoperatively so that only regions of the brain responsible for treating the motor symptoms of Parkinson's disease are stimulated."
More than 80,000 Australians are living with Parkinson's disease, with most people diagnosed after the age of 60, but early-onset Parkinson's disease also occurs.
The study findings have been published in the journal Brain.