Scientists are beginning to find out why people with Parkinson's disease often feel socially awkward. Parkinson's patients find it harder to recognize expressions of emotion in other people's faces and voices, according to two studies in the journal Neuropsychology. One of the studies raises questions about how deep brain stimulation, the best available treatment for patients who no longer respond to medication, more strongly affects the recognition of fear and sadness.  The other study finds that people with Parkinson's disease, compared with matched controls, often have difficulty discerning how others are feeling.

 

Parkinson’s is a progressive, neurodegenerative disorder that causes a loss of motor control and is often associated with frequent depression and dementia.

 

In one meta study, researchers at Harvard Medical School and Tufts University found that people suffering from Parkinson’s typically had some degree of problem identifying emotion from faces and voices. The researchers looked at 34 different studies using data from 1,295 participants and found a robust link between Parkinson's and specific deficits in recognizing emotions, especially negative emotions, across different types of stimuli and tasks.

 

A second study from researchers at the Centre Hospitalier Universitaire de Rennes in France found that deep-brain stimulation, compared with medication, caused a consistently large deficit in the recognition of fear and sadness. The researchers say these are two key facial expressions that, when understood, aid survival. The researchers 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.

 

Though Parkinson’s is a movement disorder, the researchers say implants affect a part of the brain that reaches across functions. They suggest that the same electrical stimulation that calms over-excited motor activity may also somehow inhibit emotional processing.