Engaging in regular exercise can help preserve the motor and non-motor function of Parkinson’s disease patients, most likely as a result of an increased release of dopamine in the brain, a small study suggests.
The study, “Habitual Exercisers Versus Sedentary Subjects With Parkinson’s Disease: Multimodal PET and fMRI Study,” was published in the journal Movement Disorders.
While the mechanisms underlying these benefits are largely unknown, researchers hypothesize that exercise may enhance dopamine release. The progressive degeneration and death of nerve cells in the brain that produce dopamine, called dopaminergic neurons, is one of the underlying causes of Parkinson’s disease.
In this study, researchers investigated how dopamine release and other clinical features of Parkinson’s disease differ between patients who exercise and those who remain sedentary.
A total of 17 patients with mild to moderate Parkinson’s disease were recruited, eight of whom engaged in regular exercise at least three times a week for more than three hours total, while nine were sedentary.
All patients underwent two positron emission tomography (PET) scans, one before and one after exercising on a stationary cycle, to determine whether exercise affects the release of natural dopamine in the dorsal striatum — a region of the brain involved in the control of movement. PET scans were performed after overnight withdrawal from dopaminergic medication.
Additionally, participants underwent functional magnetic resonance imaging (MRI) of the brain during a monetary reward task that required randomly selecting one of four cards.
“Subjects were explicitly informed about the probability of obtaining a monetary reward ($0.50) for selecting a winning card during each block. Subjects were also instructed that the task was purely chance (analogous to a slot machine), and there was no pattern to learn that could improve odds,” the researchers wrote.
However, for each selected card, subjects were provided visual (happy or sad face) and auditory (cheers or sighs) feedback, which could alter the card selection process, even though the success of each trial was by chance.
This test allowed researchers to evaluate possible behavioral differences in card selection between groups. Specifically, researchers measured the response of the brain’s ventral striatum, a region involved in the evaluation of rewards.
Participants also completed other tests to evaluate motor and non-motor function, including the Beck Depression Inventory to assess depression and the Starkstein Apathy Scale to measure apathy.
Results showed that habitual exercisers had an increased release of dopamine compared with sedentary patients. They also had greater activation of ventral striatum during the MRI reward task. Their apathy and bradykinesia scores were also lower than sedentary patients.
These results suggest that exercise is associated with improved motor and non-motor functions in Parkinson’s patients, which is likely linked to exercise-enhanced dopamine release.
“Although it appears that exercise plays a role in the clinical outcome of subjects with PD, future randomized control trials are needed to determine the cause-effect relationship between exercise and enhanced DA [dopamine] release, response to anticipation of reward, and clinical outcomes,” the researchers wrote.
“Future studies should also investigate other potential mechanisms of benefit from exercise,” they added.