Effects of implied physical effort in sensory-motor and pre-frontal cortex during language comprehension

Embodied theories of conceptual knowledge suggest that sensory-motor representations of actions similar to those involved in the performance of the action described are recruited during language comprehension. The extent of this recruitment, however, and the brain mechanisms supporting this process remain unknown. Using fMRI, we investigated these issues by examining how people understand sentences that convey three different degrees of physical effort and by comparing this process to action execution. To understand the effort implied by the stimulus sentences, object and action properties associated with nouns and verbs respectively needed to be integrated: pushing the piano implies more physical effort than pushing the chair. Results indicated that a pre-motor region, which was also active in action execution, was sensitive to the degree of effort implied by the language. Interestingly, the anterior inferior frontal gyrus, a region typically associated with semantic processing, was not active in action execution but was nevertheless modulated by the effort implied. Inter-region correlations also suggested that this region was strongly correlated with pre-motor and posterior temporal regions. Overall, results suggest that (a) language understanding elicits action representations retaining a degree of specificity that was previously unsuspected, including unique properties of interactions with objects, and (b) these representations, which result from integrating the words' semantic information, may be computed within a collaborative neural network that includes the anterior inferior frontal gyrus.