Imagine talking to another person and realizing you couldn’t tell whether he was angry, sad, fearful or disgusted.
That describes the challenge of many people with Parkinson’s disease, a brain disorder that leads to tremors and slurred speech, and now also appears to impair a person’s ability to read the emotions of others.
In the March issue of Neuropsychology, scientists from the Harvard Medical School and Tufts University analyzed 34 different studies of 1,295 people, finding that people with Parkinson’s often have difficulty recognizing negative emotions in others.
In various studies, people with and without Parkinson’s were asked to look at a series of photos depicting different facial expressions or asked to listen to voices that conveyed different emotional states. In some studies, participants were asked to label what a facial expression suggested while in others they were asked to compare two expressions and distinguish between them.
Heather Gray, a psychiatry instructor at Harvard and lead author of the analysis, said in an e-mail message that people with Parkinson’s disease had trouble understanding all kinds of emotions but found it particularly difficult to make sense of negative emotions, including anger, disgust, fear and sadness.
Why the disease has this effect isn’t clear. Researchers speculate that Parkinson’s may take a bigger toll on certain neural circuits that are involved in recognizing negative emotions.
Parkinson’s disease occurs when nerve cells that produce dopamine are impaired or die. Dopamine is essential to coordinated body movement, and when dopamine-producing cells are damaged, the tremors, balance problems and other symptoms typical of Parkinson’s begin to appear.
A separate study led by French researchers suggests that one of the common treatments for Parkinson’s, deep brain stimulation, may exacerbate the emotion recognition problem. The study, also published in Neuropsychology, compared the ability to recognize facial emotions in 44 people with advanced Parkinson’s and 30 healthy control subjects. About half those with Parkinson’s had undergone implantation of stimulators, while the others were receiving drug treatment as they waited for the implant procedure. The brain stimulators are electrical devices that normalize the nerve signals that control movement.
Before implantation of the stimulators, all participants read facial expressions equally well. But three months after treatment, the patients with the stimulators were significantly worse at recognizing fear and sadness compared with the other patients who had advanced Parkinson’s or to the healthy controls. Patients with stimulators confused emotions, such as misreading anger as surprise. Sometimes they interpreted the expression of a negative emotion like fear or sadness to indicate no emotional response at all.
The findings that Parkinson’s affects a person’s ability to read another’s emotional state may have a significant impact on long-term health because it could lead to social isolation, said Dr. Gray.
“Over the long run, people who have trouble understanding others’ emotional states struggle to maintain healthy social relationships,’’ said Dr. Gray. “And that, we know, has significant health consequences.’’
The information is also important for family members and caregivers who spend time with someone who has Parkinson’s. “It’s important to recognize that these communications difficulties might also be present,’’ she said. “Then, everyone can take steps to communicate more clearly and avoid a lot of frustration.’’
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