Aerobic Exercise Stalls Brain Atrophy in Parkinson’s Disease
Post by Anastasia Sares
The takeaway
Compared to a regimen of stretching, aerobic exercise (riding a stationary bike) helped people with Parkinson’s disease maintain cognitive control. It also changed the connectivity within cognitive and motor regions of the brain. This offers us some clues as to how exercise can stall the progression of symptoms in Parkinson’s disease.
What's the science?
In Parkinson’s disease, dopamine-producing cells in a brain region called the substantia nigra begin to atrophy and die. This leads to many different symptoms, including tremors, difficulty with movement, emotional changes, and cognitive decline. The substantia nigra is part of the basal ganglia, a series of nuclei (clusters of neurons) near the middle of the brain, which have strong connections to the motor cortex, helping us decide when and how to perform movements. In Parkinson’s, researchers have observed a shift in which basal ganglia regions are connected to the motor cortex. Specifically, the posterior putamen inevitably deteriorates over the course of the disease, and its function is gradually taken over by the anterior putamen.
Some drugs can slow the progression of Parkinson’s, but lately, researchers are looking into non-drug therapies to complement a patient’s medication. Simple aerobic exercise is an example of such a therapy: it has been shown to slow the progression of Parkinson’s symptoms in both animal and human studies. This week in Annals of Neurology, Johansson and colleagues compared aerobic exercise to stretching, this time asking: what exactly does this kind of exercise do to the brain?
How did they do it?
The study was part of a clinical trial, which was designed to evaluate the effect of exercise on Parkinson’s symptoms. The trial was carefully designed: all the participants had mild to moderate Parkinson’s, and were randomly assigned to a therapy involving either aerobic exercise or stretching. They were evaluated before and after the therapy. This is called an active control study—the goal is to compare two active groups, as opposed to one active group and one passive group. This way, both groups go through the same experience of being in contact with the researcher, scheduling their therapy, and following up— which can have placebo effects of their own that aren’t of interest to the researcher.
A subset of the participants volunteered to undergo MRI scans. The authors measured their brain structure as well as recording brain activity at rest. Finally, participants performed a cognitive control test, where they had to stare at a screen and then move their eyes towards a small dot or away from it, depending on the color of another dot in the center of the screen. The authors measured their eye movements and recorded correct/incorrect responses.
What did they find?
First, the authors looked at measures of overall gray matter (brain tissue that houses neuronal cell bodies). In Parkinson’s and other degenerative diseases, thinning gray matter can be a sign of neural atrophy. In the group that had done the aerobic exercise, however, there was no sign of this atrophy for the 6-month period of the study. Next, the authors looked at neural connectivity. As mentioned above, in the normal course of Parkinson’s, they expected to see a shift in connectivity of the motor cortex—after six months, the motor cortex should shift from being more connected with the posterior putamen to being more connected with the anterior putamen. This compensatory mechanism was strengthened in patients from the aerobic exercise group. Finally, the patients in the aerobic exercise condition improved on the cognitive control test. This came along with increased connectivity in frontal networks in the brain (executive control).
What's the impact?
This study is among many others showing how body and brain health are connected, and how exercise has far-reaching benefits beyond mere physical strength. These findings have important implications for the impact of aerobic exercise on stabilizing disease progression. Future studies could test whether these insights also apply to other neurodegenerative conditions.