Researchers at Washington University’s School of Medicine have discovered a possible treatment for victims of stroke whose symptoms include motor neglect by using known treatments for Parkinson’s disease. Dopamine, a chemical associated with pleasure sensation, was found to be the critical link between treatment for Parkinson’s disease and stroke.
In stroke patients, neglect can be defined as the inability to respond to a stimulus on the opposite side of a brain lesion, usually in the right hemisphere. There are several types of neglect, including spatial neglect, where a person does not detect stimulus on one half of the visual field, and motor neglect, where there is a delay in physically reacting to the stimulus.
To differentiate between the two types of neglect, researchers created an experiment in which stroke patients were shown two targets, one in each half of the visual field, and asked to respond to this stimulus. If the subjects simply had a delayed recognition time, this would indicate a spatial neglect, whereas recognizing that a stimulus was present but taking a long time to press the button would indicate motor neglect.
“It is not yet known if neglect is one syndrome or a family of syndromes. It was never actually done systematically-breaking up the syndrome into specific types,” said Ayelet Sapir, a post-doctoral researcher in neurology.
Motor neglect can be a serious problem for stroke patients in day-to-day activities. For instance, driving with neglect can be difficult because there are no outward indicators of problems, but reaction time is compromised.
The potential link between motor neglect and Parkinson’s disease was found through the analysis of MRI scans of stroke victims with motor neglect, isolating which areas suffered from similar damage.
The answer was clear: all right hemisphere stroke victims with motor deficit showed damage in the putamen, a subcortical region of the brain.
“Those patients who didn’t have a motor deficit didn’t have lesions. That’s as strong as it gets. That means the putamen must be involved,” said Sapir.
Coincidentally, Parkinson’s disease had been linked to problems with the putamen as well.
While the putamen is not actually damaged in Parkinson’s patients, it is responsible for receiving dopamine signals from the substantia nigra, a region significantly destroyed in Parkinson’s disease. This lack of dopamine signaling creates problems with muscle contractions, leading to decreased reaction time, just like in motor neglect.
“It may be interesting to try treating stroke patients with dopamine. This has been tried in the past and the results were kind of mixed, because probably only some patients will benefit from it and some patients will not,” said Sapir. “It may be more complicated than just [giving] dopamine to stroke patients.”
Sapir explained that the ultimate goal of her research would be to get a clinical trial and start treating patients. Before this, however, Sapir wants to identify more types of neglect and if we can isolate a brain region with them. For example, object-based neglect and spatial neglect are still not pinpointed to a certain region of the brain.
“Now that we found the region, it is possible to treat them not only with dopamine but other treatments. For instance, something that is also done in Parkinson’s is deep brain stimulation to reduce imbalance.”
Sapir is the lead author of this research project, whose findings are published in the Journal of Neuroscience.
Undergraduate Julie Kaplan, a junior, also participated in the collection and analysis of the stroke data.
“I really liked working directly with the patients. Giving the behavioral tests was pretty interesting,” said Kaplan, a philosophy-neuroscience-psychology major. “It was a great experience just to be in a lab environment and [to be able to participate] in all parts, from the computational analysis to the behavioral tasks.”