Cerebral Correlates of Robot-Assisted Upper Limb Motion Driven by Motor Intention in Healthy Individuals: An fNIRS Study

The past few years have seen an exponential growth of the robot-assisted rehabilitation field and new technological developments allowing the integration of the user's intention through detection of physiological information. The inclusion of motor intention is thought to be promising for motor rehabilitation and to facilitate neuroplasticity potentially by stimulating the cortical circuitry more than, or at least differently from, non-voluntary passive motion. Yet, contrasting results are reported in the literature. We aimed here to investigate the importance of the integration of motor intention on cortical activity using functional near-infrared spectroscopy (fNIRS) by comparing the active use of an assistive exoskeleton targeting the shoulder with passive use and unassisted motion. We recorded the activity of the bilateral frontal and parietal cortices of 20 healthy individuals during an arm raising task. Active robot assistance showed similar activity patterns to unassisted motion with the exception of a greater activation of the prefrontal region. Correlates of intention could be confirmed by an activation of the supplementary motor area in active-assisted and unassisted but not passive condition. Activation of the contralateral primary sensorimotor regions did not differ between passive and active conditions but activity of the ipsilateral hemisphere and secondary regions was reduced during passive motion. Our results provide arguments in favor of the integration of the user's intention through physiological signals for rehabilitation, in favor of the investigation of secondary and ipsilateral regions, and in favor of the use of fNIRS to investigate differences in cortical correlates of passive and active motion.