The functional role of motor activation in language processing: Motor cortical oscillations support lexical-semantic retrieval

There is increasing experimental evidence that processing action-related language results in the automatic activation of associated regions of the motor and premotor cortex. However, the functional significance of motor activation in language processing is still under debate. In the present EEG study, we set out to investigate if language-induced motor activation primarily reflects the retrieval of lexical-semantic information or post-lexical motor imagery. The processing of action verbs was found accompanied by an early activation of motor-related brain areas, as reflected by a desynchronization in the mu- and beta-frequency bands which was localized to motor and premotor areas. A stronger motor activation was observed for verbs presented in an animal context (e.g. "The deer jumped over the stream") compared to a human context (e.g. "The athlete jumped over the fence") and motor resonance was directly modulated by the cloze probability of the noun-verb pairs. The onset of the motor effects preceded classical measures of semantic integration (i.e. the N400 component) and the strength of motor activation was found inversely related to the size of the N400 effect. These findings support the hypothesis that motor activation in language processing primarily supports the retrieval and integration of lexical-semantic information.