An electrophysiological investigation of action observation: evidences for integration of suboptimal movement performances

Neural priming and facilitation phenomena have been observed in sensorimotor cortical regions during observation of actions. The effects of such visual-motor facilitation have been shown via non-invasive brain stimulation (NIBS) and imaging techniques. Related mechanisms proved to be modelled by practice and influenced by previous motor expertise. Nonetheless, the role of expertise has been primarily studied by focusing on high-level motor proficiency, while the potential effects of coding suboptimal motor performances is still unclear. A first NIBS study highlighted that the responsivity of the sensorimotor system can be modulated by observing poorly-executed actions. To better understand those evidences, we devised an electrophysiological (EEG) study to explore functional correlates of the observation of optimal vs. suboptimal execution of complex actions. Electroencephalographic data have been recorded from twenty right-handed healthy young adults while they observed 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 the Nine Hole Peg Test (NHPT), a test tapping on fine motor abilities. EEG data have been processed to extract frequency-domain metrics. Frequency-domain data have been analysed taking into account trials and conditions, so to also explore habituation trends. We observed globally lower beta power during the observation of patients’ videos with respect to confederate’s videos, even when he simulated poor motor performances. Again, beta activity over somatosensory areas gradually increased across reiterations of the minimally-impaired patient’ video. Those evidences corroborate the hypothesis that familiarity with peculiar kinematic patterns might modulate sensorimotor responses to observed actions and they might mirror a progressive integration of slightly suboptimal motor performances into participants’ motor schemata. Further, present findings may inform on the innate sensitivity and responsivity of human sensorimotor system.