Parkinson's Patients' Upper and Lower Limb Motor Impairments Differentially Influence Action Verb Processing

Theories of grounded cognition emphasize the role of sensorimotor simulation in conceptual knowledge. With regard to action concepts, the motor system is hypothesized to play a central role in their representation and processing. The present study investigates whether patients with Parkinson’s disease (PD) who have greater upper versus greater lower limb impairments show different patterns of performance when processing action verbs. Patients and matched controls made action decisions on upper-limb (reach), lower-limb (kick), and psych verbs (think). The most important result was an interaction between PD dominance (PD upper vs. lower limb motor impairments) and verb type (uppervs. lower-limb verbs). PD patients with greater upper limb impairment were slower in processing upper-limb versus lower-limb verbs, whereas those with greater lower limb impairment performed similarly on these verb types. The results support a relatively fine-grained functional role of the motor system in the conceptual representation of action verbs.