Parkinson's disease patients have trouble recognizing expressions of emotion in other people's faces and voices, according to two new studies.
Parkinson's is a neurodegenerative disorder, causes tremors, stiffness and balance problems, as well as fairly frequent depression and dementia.
In the March issue of Neuropsychology, Heather Gray and Linda Tickle-Degnen found that people with Parkinson's disease, compared with matched controls, often have difficulty discerning how others are feeling.
Their meta-analysis of 34 different studies using data from 1,295 participants shows a robust link between Parkinson's and specific deficits in recognizing emotions, especially negative emotions, across different types of stimuli and tasks.
The meta-analysis, conducted at Harvard Medical School and Tufts University, found that patients typically had some degree of problem identifying emotion from faces and voices.
Further clarification is provided in a second study, published in the January issue of Neuropsychology, that showed that deep-brain stimulation, compared with medication, caused a consistently large deficit in the recognition of fear and sadness - two key facial expressions that, when understood, aid survival.
Led by Julie Peron, at the Centre Hospitalier Universitaire de Rennes in France, the research team compared the ability of people with Parkinson's in three different groups to recognize facial emotions:
24 advanced patients implanted with deep-brain stimulators after they didn't respond or were sensitive to oral levodopa (the usual drug for the disease); 20 advanced patients given apomorphine hydrochloride by injection or infusion pump while they waited an implant; and 30 healthy controls.
Researchers tested all participants using standard photographs of facial expression before and three months after they were treated. Before implantation of the stimulators, all participants read facial expressions equally well.
Patients in the surgical group were implanted with stimulators, electrical devices that prod the brain's subthalamic nucleus, a small, lens-shaped structure, to normalize the nerve signals that control movement. This nucleus is part of the basal ganglia system, which is thought to integrate movement, cognition and emotion.
Three months after treatment, only the patients with stimulators - not the drug-treated patients or the healthy controls - were significantly worse at recognizing fear and sadness. Patients with stimulators confused those expressions with others, such as surprise, or even no emotion.
Medicated patients and healthy controls were either accurate about fear and sadness or occasionally mistook them for other negative emotions, such as disgust.
"Having Parkinson's predisposes an individual to errors in emotion recognition. The research in France, along with previous studies, indicates that deep-brain stimulation produces an even more severe deficit," said Gray.