Deficits in decoding emotional facial expressions in Parkinson's disease

The basal ganglia have numerous connections not only with the motor cortex but also with the prefrontal and limbic cortical areas. Therefore, basal ganglia lesions can disturb motor function but also cognitive function and emotion processing. The aim of the present study was to assess the consequences of Parkinson's disease (PD) on ability to decode emotional facial expressions (EFEs)-a method commonly used to investigate non-verbal emotion processing.

Eighteen PD patients participated in the study, together with 18 healthy subjects strictly matched with respect to age, education and sex. The patients were early in the course of the disease and had not yet received any antiparkinsonian treatment. Decoding of EFEs was assessed using a standardized, quantitative task where the expressions were of moderate intensity, i.e. quite similar to those experienced in everyday life. A set of tests also assessed executive function. Visuospatial perception, depression and anxiety were measured.

Early in the course of the disease, untreated PD patients were significantly impaired in decoding EFEs, as well as in executive function. The deficits were significantly interrelated, although neither was significantly related to severity of the motor symptoms. Visuospatial perception was not impaired, and the patients' impairment was related neither to their depression nor to their anxiety score. The PD patients' impairment in decoding EFEs was related to a systematic response bias.

Early in the course of PD, non-verbal emotional information processing is disturbed. This suggests that in PD, nigrostriatal dopaminergic depletion leads not only to motor and cognitive disturbances but also to emotional information processing deficits. The observed correlation pattern does not enable adoption of a clear-cut position in the debate over totally or partially segregated functional organization of the basal ganglia circuits.