Study Finds Why Parkinson's Treatment Elicit Compulsive Behaviours

A novel discovery that may help explain why standard drug treatment elicits compulsive behaviours in Parkinson's patients. has been made by scientists.

They provide new insights into the brain mechanisms that underlie a predisposition to behavioural addictions, such as pathological gambling and shopping.

Parkinson’s Disease - Causes, Symptoms, Diagnosis, Treatment
Parkinson’s disease is a neurodegenerative disease caused by progressive dopamine brain cells loss. Symptoms of Parkinson’s disease are correctable to an extent.

The tendency to make a compulsive choice, even when faced with substantial negative outcomes and alternative choices, is characteristic of aberrant gambling or shopping behaviors.

Therefore, it is likely that the decision-making process is disrupted in individuals who demonstrate these compulsive behaviours.

The researchers believe that abnormalities in "prediction error," which serves as a kind of teaching signal to update our future predictions and influence future choices, might play a role in substance abuse disorders.

Parkinson's Disease
Slide animation on Parkinson disease. It is a progressive movement disorder due to degeneration of nerve cells of the substantia nigra of the brain. The symptoms get worse with time but drugs or surgery can control them. PD cannot be cured.

However, prediction error has not yet been linked to such human behavioural pathologies.

Dr. Valerie Voon, from the National Institutes of Health, led a study of compulsive behaviours triggered in Parkinson's disease patients treated with drugs that stimulate the brain's dopamine system.

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Slide animation on surgery for Parkinson disease. Surgery is only indicated where drugs fail to control the symptoms of this progressive movement disorder. Surgery cannot cure the disease.

"A constellation of pathological behaviours, including gambling, shopping, binge eating, and hypersexuality, is seen in13pct of patients taking dopamine agonists," said Voon.

"These behaviours are associated with factors predisposing to general substance abuse disorders, thus emphasizing a common underlying susceptibility," Voon added.

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During the study, researchers used brain imaging techniques to examine dopamine agonist-induced compulsive behaviors in Parkinson's patients and normal controls.

The researchers observed that dopamine agonists elicited an increase in the rate of learning from beneficial outcomes and a greater prediction error, signifying a better than expected outcome, in susceptible individuals with Parkinson's disease.

"Taken together, our findings are consistent with a model whereby a distorted estimation of the gain underpins a choice bias towards gains," said Voon.

"The results highlight a key decision-making process dysregulated by dopamine agonists in a population susceptible to compulsive behaviors and provide clues to mechanisms that underlie behavioral escalation in a disorder of behavioral addiction

"The mechanism may also explain why anecdotally some patients describe the onset of their gambling symptoms after experiencing a 'win'," Voon added.

The study appears in journal Neuron.

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