Actual, sham and no-feedback effects in motor imagery practice

Motor imagery (MI) has been associated to clinical benefits for motor and cognitive rehabilitation protocols through the appropriate identification and training of its corresponding neural patterns. Although potentially impactful factors for MI practice have been identified, issues regarding system feedback and the underlying neurophysiological alterations such practice can produce still remain. In this work, we investigated how feedback can affect the outcome of a MI practice protocol with a brain-computer interface (BCI), when providing: no feedback, sham feedback or actual neurofeedback. We assessed whether event-related desynchronization occurrence (EO) and classification accuracy (CA) varied in each scenario. We found that: (i) practice without feedback did not enhance either metric; (ii) sham feedback yielded a wider variety of outcomes than for the control group, but no statistical significance was observed at the group level; (iii) although users trained to adapt to the BCI classifier, improvements in CA and both contra and ipsilateral EO were observed for the neurofeedback group: average CA increased from (71.3 +/- 3.7) % to (75.5 +/- 5.8) %, whereas median EO increased approximately 5% per session This study reinforces the relevance of neurofeedback in MI learning and provides new insights into neurophysiological correlates throughout the practice protocol. We also hint at a possible placebo effect that provides significant correlations between EO and CA only for the sham group.