Multiple representations for complex everyday gestures: hemodynamic (fNIRS) correlates of action observation, execution, and listening

Objective: Actions are complex events characterized by multimodal representations. Following the common coding theory, perceptual and motor representations of actions are linked by a common computational code and share common neural substrates. Further, according to the embodied semantics theory, even coding of linguistic material may be fostered by perceptual and motor systems. The present work thus aimed at exploring potential associations of perceptual, motor and linguistic representations of complex real-life actions. In particular, we were interested in hemodynamic activation patterns within sensorimotor areas induced by the observation of such motor acts or the listening to their verbal description. Participants and Methods: Twenty volunteers took part in the study. The experimental design included five blocked conditions: action execution; action observation; listening to brief verbal descriptions of actions; action observation coupled with listening to their verbal description; and action execution coupled with listening to their verbal description. Hemodynamic activity in premotor and sensorimotor cortical regions was monitored and recorded via optical imaging (functional Near-Infrared Spectroscopy – fNIRS). Results: Hemodynamic data analysis showed that activation in left cortical regions was the lowest during observation of complex actions and observation coupled with listening of description of actions, greater during simple listening of verbal description of actions, and maximal when participants actually executed complex actions and when execution was coupled with listening to consistent verbal descriptions. Conclusions: Findings began hinting at potential practical implications of using verbal description of actions to modulate the activation of specific structures constituting the sensorimotor network and at their potential for prompting the access to stored action representations via alternative neural pathways.