Functional correlates of perceptual, motor and linguistic representations of complex actions: electrophysiological and optical imaging data

Similarities between action observation and action execution processes – as well as action imagination and simulation ones – have been consistently reported to date by electrophysiological, neuroimaging and brain stimulation studies. According to the common coding hypothesis, perceptual and motor representations are associated and ground on a common computational code. Observing an action, then, would prime the relative action representation, and executing an action would facilitate relative representations of its perceivable effects. Furthermore, a link has been suggested between motor and conceptual-linguistic representations of actions and supported, for example, by behavioural evidences on the action-sentence compatibility effect. The present study aims at extending existing observations on simple actions and at investigating electrophysiological (EEG) and hemodynamic (functional Near-Infrared Spectroscopy, fNIRS) correlates of the execution and observation of complex common actions. So to explore potentially shared encoding processes with respect to conceptual-linguistic representations of those actions, we also looked at cortical correlates of listening to their relative verbal descriptions. Twenty healthy young adults took part in the study and were asked to: observe realistic complex actions (e.g. to pour some wine), actually execute them, or listen to their verbal description (brief verb and object phrases, e.g. “pour some wine”). We also included two combined tasks (observation and listening; execution and listening) so to investigate potential cross-facilitation effects. The integrated recording setup included 15 evenly distributed EEG electrodes and 16 fNIRS channels (over bilateral prefrontal and pre-motor regions). The analysis of EEG data highlighted the role of contralateral sensorimotor areas in all experimental tasks, as marked by a modulation of the upper-alpha band, and task-specific modulations of oscillatory activity over midline electrodes. Conversely, fNIRS prefrontal and pre-motor hemodynamic responses mainly highlighted task-specific peculiarities, with greater contralateral activity during action execution, lower activation during action observation, and no relevant hemispheric asymmetries during the listening conditions. To sum up, electrophysiological findings pointed out interesting similarities in motor and somatosensory cortical activity during observation, execution and listening conditions even when focusing on realistic actions, in line with common coding theories. Task specificities revealed by fNIRS measures might instead mirror the differential role of anterior cortical structures.