Can passive mobilization provide clinically-relevant brain stimulation? A pilot EEG and NIRS study on healthy subjects.

Lower limb rehabilitation is a fundamental part of post-acute care in neurological disease. Early commencement of active workout is often prevented by paresis, thus physical treatment may be delayed until patients regain some voluntary command of their muscles. Passive mobilization of the affected joints is mostly delivered in order to safeguard tissue properties and shun circulatory problems. The present paper investigates the potential role of early passive motion in stimulating cortical areas of the brain devoted to the control of the lower limb. An electro-mechanical mobilizer for the ankle joint (Toe-Up!) was implemented utilizing specially-designed shape-memory-alloy-based actuators. This device was constructed to be usable by bedridden subjects. Besides, the slowness and gentleness of the imparted motion, make it suitable for patients in a very early stage of their recovery. The mobilizer underwent technical checks to confirm reliability and passed the required safety tests for electric biomedical devices. Four healthy volunteers took part in the pre-clinical phase of the study. The protocol consisted in measuring of brain activity by EEG and NIRS in four different conditions: rest, active dorsiflexion of the ankle, passive mobilization of the ankle, and assisted motion of the same joint. The acquired data were processed to obtain maps of cortical activation, which were then compared. The measurements collected so far show that there is a similar pattern of activity between active and passive/assisted particularly in the contralateral premotor areas. This result, albeit based on very few observations, might suggest that passive motion provides somatosensory afferences that are processed in a similar manner as for voluntary control. Should this evidence be confirmed by further trials on healthy individuals and neurological patients, it could form a basis for a clinical use of early passive exercise in supporting central functional recovery.