MRCP as a biomarker of motor action with varying degree of central and peripheral contribution as defined by ultrasound imaging

Introduction: \ud Motor imagination is an alternative rehabilitation strategy for people who cannot execute real movements. However it is still a matter of debate to which degree it involves activation of deeper muscle structures, which cannot be detected by surface electromyography (SEMG). \ud \ud Methods: \ud Eighteen able bodied participants performed cue based isometric ankle plantar flexion (active movement) followed by active relaxation under four conditions: executed movements with two levels of muscle contraction (fully executed and attempted movements, EM and AM) and motor imagination with and without detectable muscle twitches (IT and I). Most prominent peaks and distinctive phases of Movement Related Cortical Potential (MRCP) were compared between conditions. Ultrasound imagining (USI) and SEMG were used to detect movements. \ud \ud Results: \ud IT showed spatially distinctive significant difference compared to both I and AM during active movement preparation and re-afferentation phase; further wide spread differences were found between IT and AM during active movement execution and posteriorly during preparation for active relaxation. EM and AM showed largest difference frontally during active movement planning and posteriorly during executing of active relaxation. Movement preparation positivity P1 showed significant difference in amplitude between IT and AM but not between IT and I. \ud \ud Conclusion: \ud USI can detect subliminal movements (twitches) better than SEMG. MRCP is a biomarker sensitive to different levels of muscle contraction and relaxation. IT is a motor condition distinguishable from both I and AM. Significance: EEG biomarkers of movements could be used to identify pathological conditions, that manifest themselves during either active contraction or active relaxation.