Where is the action? Action sentence processing in Parkinson's disease.

According to an influential view of conceptual representation, action concepts are understood through motoric simulations, involving motor networks of the brain. A stronger version of this embodied account suggests that even figurative uses of action words (e.g., grasping the concept) are understood through motoric simulations. We investigated these claims by assessing whether Parkinson's disease (PD), a disorder affecting the motor system, is associated with selective deficits in comprehending action-related sentences. Twenty PD patients and 21 age-matched controls performed a sentence comprehension task, where sentences belonged to one of four conditions: literal action, non-idiomatic metaphoric action, idiomatic action, and abstract. The same verbs (referring to hand/arm actions) were used in the three action-related conditions. Patients, but not controls, were slower to respond to literal and idiomatic action than to abstract sentences. These results indicate that sensory-motor systems play a functional role in semantic processing, including processing of figurative action language.