People with Parkinson’s disease often can’t differentiate between a sweet smile or an angry grimace, a warm welcome or a rude remark. And one of the major treatments may be making this worse, according to new research.
The debilitating movement disorder starts with tiny tremors and gradually seizes an individual’s ability to control movement, including speech. But it also often contributes to dementia, personality changes and other mental deficits, as countless doctors, researchers and families dealing with the disorder have documented. People with Parkinson’s disease often become socially withdrawn and uncomfortable.
This social uneasiness may stem from the decreased ability of Parkinson’s sufferers to understand other people’s emotions, according to a study published in the March issue of Neuropsychology.
“The idea here is that some of the brain regions that are impaired in Parkinson’s are also the brain regions that we use when we are interpreting emotion in other people, whether it be from the face of from the voice,” said lead author Heather Gray, psychiatry instructor at Harvard Medical School in Cambridge, Mass.
Gray explained that Parkinson’s disease affects the basil ganglia area, located at the base of the brain, which controls involuntary movement and emotion in the brain. The disease results in the loss of nerve cells that produce dopamine, the brain’s “feel-good” chemical that also directs the function of muscles and movement.
“There are pathways in between the basal ganglia and other areas that are involved in emotion recognition, and so if you disrupt one part of the circuit there, you disrupt the whole thing,” Gray said. She added that difficulty in emotion recognition does not necessarily have to connect directly with areas impacted by Parkinson’s disease.
Gray collected data from 34 different studies with research specific to emotion recognition in people with Parkinson’s. “From the studies, we extracted data on how well people in the two groups performed on these tasks, with the two groups being people with Parkinson’s and their matched control” without the disease, she said.
But a successful treatment for the tremors of Parkinson's may be worsening the toll the illness takes on emotional communication.
"Deep brain stimulation” – involving a surgical process that uses implanted electrodes to stimulate highly specific parts of the brain affected by a disorder – is the most common and effective treatment for advanced-stage Parkinson’s patients not responding to medications or other forms of therapy. It often dramatically reduces or even eliminates the uncontrollable movements and tremors associated with Parkinson’s disease.
No current research has found deep brain stimulation to alleviate any of the mental problems such as dementia and social awkwardness from Parkinson’s disease. In fact, it likely exacerbates the emotional processing deficits, according to French researchers at the Centre Hospitalier Universitaire de Rennes.
Their study, also published in Neuropsychology earlier this year, found that deep brain stimulation in 24 people with Parkinson’s disease significantly decreased their ability to recognize other people’s facial emotions, specifically fear and sadness.
“In my group of patients, I don’t see that as a significant problem,” said Dr. Roy Bakay, professor of neurosurgery at the Rush University Medical Center in Chicago. “For the most part, these are relatively minor trade-offs for the major benefits of brain stimulation.”
For people with Parkinson’s disease, deep brain stimulation targets one of three critical movement regions in the brain. The French study exclusively stimulated the subthalamic nucleus region in its patients. The subthalamic nucleus, located deep within the brain, is a part of the basal ganglia, which is involved in emotional processing.
The study also included a group of 20 Parkinson’s patients who underwent a different form of treatment (dopamine replacement therapy) and a control group of 30 healthy people. These groups showed no signs of emotional recognition impairment. All subjects were assessed three months before and after treatment.
“Many of these types of psychiatric and cognitive problems that occur do so shortly after surgery,” Bakay said. “Follow up is important because many of these problems go away.”
Gray agreed: “It’d be interesting to follow those people up maybe six to 12 months down the road and see if they’re still having these problems. The studies that we included in the [report] were mostly for the short term.”
Patients undergoing deep brain stimulation treatment must first have electrodes surgically implanted onto a highly specific part of the brain (usually no bigger than a thumbnail) affected by a disorder. The electrodes, wired to a pacemaker implanted near the collarbone, then provide an ongoing, externally adjustable electrical current to the brain region for a period ranging from a few months to several years. The continued stimulation of the malfunctioning brain region modifies brain circuitry and stabilizes the affected region, experts believe.
“It’s not a cure,” Bakay said. “It’s a treatment, and it does produce some side effects.”
He added, “It’s a very safe procedure for most people.”