Passive, yet not inactive: robotic exoskeleton walking increases cortical activation dependent on task

Abstract

Background: Experimental designs using surrogate gait-like movements, such as in functional magnetic resonance imaging (MRI), cannot fully capture the cortical activation associated with overground gait. Overground gait in a robotic exoskeleton may be an ideal tool to generate controlled sensorimotor stimulation of gait conditions like 'active' (i.e. user moves with the device) and 'passive' (i.e. user is moved by the device) gait. To truly understand these neural mechanisms, functional near-infrared spectroscopy (fNIRS) would yield greater ecological validity. Thus, the aim of this experiment was to use fNIRS to delineate brain activation differences between 'Active' and 'Passive' overground gait in a robotic exoskeleton. Methods: Fourteen healthy adults performed 10 walking trials in a robotic exoskeleton for Passive and Active conditions, with fNIRS over bilateral frontal and parietal lobes, and electromyography (EMG) over bilateral thigh muscles. Digitization of optode locations and individual T1 MRI scans were used to demarcate the brain regions fNIRS recorded from. Results: Increased oxyhemoglobin in the right frontal cortex was found for Passive compared with Active conditions. For deoxyhemoglobin, increased activation during Passive was found in the left frontal cortex and bilateral parietal cortices compared with Active; one channel in the left parietal cortex decreased during Active when compared with Passive. Normalized EMG mean amplitude was higher in the Active compared with Passive conditions for all four muscles (p ≤ 0.044), confirming participants produced the conditions asked of them. Conclusions: The parietal cortex is active during passive robotic exoskeleton gait, a novel finding as research to date has not recorded posterior to the primary somatosensory cortex. Increased activation of the parietal cortex may be related to the planning of limb coordination while maintaining postural control. Future neurorehabilitation research could use fNIRS to examine whether exoskeletal gait training can increase gait-related brain activation with individuals unable to walk independently.

Acupuncture With deqi Modulates the Hemodynamic Response and Functional Connectivity of the Prefrontal-Motor Cortical Network

“…Because the fNIRS recorded raw data contained various noises, fNIRS raw data was pre-processed with the MATLAB TM 17.0 (MathWorks, United States) software by the following procedure to improve the signal-to-noise ratio (SNR) (Supplementary Figure 1). Firstly, noisy channels were rejected if any of the following situations were met: (I) The optical intensity (OI) range exceeded the 0.5-1,000; (II) The source-detector separation range exceeded the range from 0 to 45; and (III) The ratio of the mean and standard deviation of the optical intensity [mean(OI)/std(OI)] is less than 2 (Huppert et al, 2009;Peters et al, 2020). Secondly, for a given subject, if the percentage of the subject's rejected channels over all channels exceeds 50%, the subject with poor signal quality was also rejected, which was in line with the previous fNIRS study (Hakuno et al, 2020).…”

Relation between Cortical Activation and Effort during Robot-Mediated Walking in Healthy People: A Functional Near-Infrared Spectroscopy Neuroimaging Study (fNIRS)

“…Although we did not directly measure muscle effort or participants’ perceptions of effort, we consider it unlikely that they were completely passive, which could explain the lack of difference between these two conditions. A study that compared passive and active modes of robotic gait found that muscle activity in the passive mode was about 50% of that recorded during the active mode [ 45 ]. Similarly to our results, brain activation levels did not differ between the two lowest effort conditions.…”

Efficacy of an exoskeleton-based physical therapy program for non-ambulatory patients during subacute stroke rehabilitation: a randomized controlled trial

“…Additionally, given that functional improvement in post-stroke walking ability is a product of neuromuscular recovery and movement compensations [ 61 ], there may have been differences between groups in the nature of walking improvement that were not captured by our included outcomes. Current research of the impact of robotic-assisted walking on other measures such as brain plasticity, muscle activation symmetry, and kinematic qualities of gait may support alternate reasons for utilizing an exoskeleton in stroke rehabilitation [ 51 , 62 , 63 ]. It is also important to consider the emotional and psychological benefit of standing and practicing walking for patients after stroke.…”