Reduced early visual emotion discrimination as an index of diminished emotion processing in Parkinson’s disease? – Evidence from event-related brain potentials

Although Parkinson’s disease (PD) is defined by its motor symptoms, it is now well recognized that cognitive and affective domains, such as recognition of emotion from facial expressions, may also be impaired. To examine brain mechanisms involved in processing of emotion recognition from facial expressions, we obtained affective ratings and visual event-related potentials (ERPs) in response to facial expressions from 18 PD patients under dopamine-replacement therapy, and 17 healthy age- and sex-matched controls. In control subjects, the early posterior negativity (EPN) of the ERP, which is thought to reflect early perceptual emotion discrimination, was larger in response to emotional compared to neutral facial expressions. In contrast, this emotional modulation of the EPN was absent in PD patients indicating impaired early emotion discrimination. Behaviorally, PD patients showed no impairments in emotion recognition as measured by affective ratings. These findings suggest that facial emotion processing may be disrupted at an early stage of visual neural processing in PD. Absence of behavioral impairment may point to compensatory strategies of emotion recognition in medicated PD patients. Further research should clarify these dissociations between behavioral and neurophysiological levels of emotion processing in PD.