Laterality of motor symptom onset and facial expressivity in Parkinson disease using face digitization

The onset of motor symptoms in Parkinson disease (PD) is typically unilateral. Previous work has suggested that laterality of motor symptoms may also influence non-motor symptoms including cognition and emotion perception. In line with hemispheric differences in emotion processing, we tested whether left side/right brain motor onset was associated with worse expression of facial affect when compared to right side/left brain motor onset. We evaluated movement changes associated with facial affect in 30 patients with idiopathic PD (15 left-sided motor onset, 15 right-sided motor onset) and 20 healthy controls. Participants were videotaped while posing three facial expressions: fear, anger, and happiness. Expressions were digitized and analyzed using software that extracted three variables: two measures of dynamic movement change (total entropy and entropy percent change) and a measure of time to initiate facial expression (latency). The groups did not differ in overall amount of movement change or percentchange. However, left-sided onset PD patients were significantly slower in initiating anger and happiness facial expressions than were right-sided onset PD patients and controls. Our results indicated PD patients with left-sided symptom onset had greater latency in initiating two of three facial expressions, which may reflect laterality effects in intentional behaviour.