Observing suboptimal movement schemas: EEG evidences for progressive sensorimotor integration

Objective Action observation is known to enhance sensorimotor system activation, and such effect has been linked to neural priming and response facilitation mechanisms. Moreover, visuo-motor facilitation and action observation processes proved to be influenced by expertise. The role of expertise, however, has been primarily studied by focusing on high-level motor proficiency. As a consequence, while it was shown that the observation of trained sport gestures is able to induce greater motor responsivity in athletes, evidences on the effect of observing poorly performed actions are still lacking. On the basis of a preliminary TMS study suggesting that motor cortex activity can be modulated even by the observation of suboptimal movement performances, we investigated electrophysiological (EEG) correlates of the observation of complex actions performed by healthy individuals and patients affected by multiple sclerosis (MS). Participants Twenty healthy young adults took part in the study and were presented with four randomly reiterated videos. Videos depicted a healthy confederate, a minimally-impaired MS patient, a mildly-impaired MS patient, or a confederate trying to simulate mild motor difficulties performing a test tapping on fine motor abilities. EEG data were recorded and analysed in the frequency-domain and across video reiterations. Results The time-series analysis of EEG frequency data highlighted globally lower beta power during the observation of patients’ videos with respect to confederate’s videos, even when he simulated poor motor performances. Further, we observed gradually increasing beta activity across videos reiterations, but specifically over somatosensory regions and for the minimally-impaired patient’ video. Conclusion We suggest that such evidences mirror a progressive integration of slightly suboptimal motor performances into participants’ motor schemata and that they further hint at the innate sensitivity and responsivity of the sensorimotor system, in line with evidences associating EEG beta desynchronization with processing of observed and executed goal-directed actions.