Action verb processing correlates with motor asymmetry in Parkinson's disease

Abstract

Onset of motor symptoms in PD is asymmetrical, and symptoms affect the side of onset more severely throughout the progression of the disease, which is known as “motor asymmetry.” Previous studies revealed that PD patients with right-motor asymmetry (more severe symptoms on the right side of body) exhibited more speech impairment than those with left-motor asymmetry (Wang et al., 2003; 2006). Patients with active deep brain stimulation (DBS) exhibited more severe speech deficits when they received either bilateral or left-only stimulation of the subthalamic nucleus (STN) than receiving right-only STN stimulation (Santens et al., 2003). These findings lead to the current hypothesis that there is correlation between the motor asymmetry and linguistic processing of action verbs. Using a novel action verbal processing paradigm, 24 PD patients (12 right- and 12 left-motor asymmetry) and 11 age- gender-matched healthy controls were tested. The results showed that when the motor asymmetry was sufficiently different, i.e., when the difference of the UPDRS scores between the two sides of the body is greater than 2 (points), the right-motor asymmetry patients took longer to process the action verbs, supporting the hypothesis that motor asymmetry is correlated with linguistic processing of action verbs at the cortical level.