Grasping the Idea – With Your Hands? A tDCS Investigation of Embodied Simulation in Motor Metaphors

Reading literal descriptions of motor actions, like grasp the pen, leads to activation in corresponding areas of the motor and premotor cortices. According to theories of embodied cognition (e.g., Barsalou, 1999), such activation reflects embodied simulation of the motor action described in the text - a “partial re-experiencing” that activates the same neural areas as performing the action.The present study investigates whether motor simulations are similarly activated when action words are used nonliterally, as in the motor metaphor grasp the idea. I used anodal transcranial direct current stimulation (tDCS) to increase neuronal excitability in the left primary motor cortex while participants (N = 55) read short sentences and judged whether each sentence made sense. Participants read four categories of sentences: literal motor sentences (e.g., the architect grasped the pen), literal non-motor sentences (e.g. the student understood the idea), nonsense sentences (e.g. the man browsed the ball), and motor metaphors (e.g., the student grasped the idea), which varied in familiarity. Neurostimulation (anodal TDCS) significantly facilitated processing of literal motor sentences and motor metaphors, but not literal non-motor or nonsense sentences. Within motor metaphors, neurostimulation significantly facilitated processing of unfamiliar but not familiar expressions. These results indicate that embodied motor simulation facilitates processing of both literal and figurative uses of motor action words, suggesting that the figurative meaning is grounded in the literal meaning. In motor metaphors, the importance of embodied simulation decreases as familiarity increases, suggesting that the embodied pathway is eventually replaced with faster, non-embodied processing pathways as familiarity increases.