Disturbance of spontaneous and posed facial expressions in Parkinson's disease

The effects of Parkinson's disease (PD) on spontaneous and posed facial activity and on the control of facial muscles were assessed by comparing 22 PD patients with 22 controls. Facial activity was analysed using the Facial Action Coding System (FACS; Ekman & Friesen, 1978). As predicted, PD patients showed reduced levels of spontaneous and posed facial expression in reaction to unpleasant odours compared to controls. PD patients were less successful than controls in masking or intensifying negative facial expressions. PD patients were also less able than controls to imitate specific facial muscle movements, but did not differ in the ability to pose emotional facial expressions. These results suggest that not only is spontaneous facial activity disturbed in PD, but also to some degree the ability to pose facial expressions, to mask facial expressions with other expressions, and to deliberately move specific muscles in the face.