Frontiers in Neuroscience (Aug 2016)
Control of an ambulatory exoskeleton with a brain-machine interface for spinal cord injury gait rehabilitation
Abstract
The closed-loop control of rehabilitative technologies by neural commands has shown a greatpotential to improve motor recovery in patients suffering from paralysis. Brain-machine interfaces(BMI) can be used as a natural control method for such technologies. BMI provide a continuousassociation between the brain activity and peripheral stimulation, with the potential to induceplastic changes in the nervous system. Paraplegic patients, and especially the ones with incompleteinjuries, constitute a potential target population to be rehabilitated with brain-controlledrobotic systems, as they may improve their gait function after the reinforcement of their sparedintact neural pathways. This paper proposes a closed-loop BMI system to control an ambulatoryexoskeleton–without any weight or balance support–for gait rehabilitation of incomplete spinalcord injury (SCI) patients. The integrated system was validated with three healthy subjects, andits viability in a clinical scenario was tested with four SCI patients. Using a cue-guided paradigm,the electroencephalographic signals of the subjects were used to decode their gait intention, andto trigger the movements of the exoskeleton. We designed a protocol with a special emphasison safety, since patients with poor balance were required to stand and walk. We continuouslymonitored their fatigue and exertion levels, and conducted usability and user-satisfaction testsafter the experiments. The results show that, for the three healthy subjects, 84.44□14.56% ofthe trials were correctly decoded. Three out of the four patients performed at least one successfulBMI session, with an average performance of 77.61□14.72%. The shared control strategyimplemented (i.e., the exoskeleton could only move during specific periods of time) was effectivein preventing unexpected movements during periods in which patients were asked to relax. On average, 55.22□16.69% and 40.45□16.98% of the trials (for healthy subjects and patients,respectively) would have suffered from unexpected activations (i.e., false positives) without theproposed control strategy. All the patients showed low exertion and fatigue levels during theperformance of the experiments. This paper constitutes a proof-of-concept study to validate thefeasibility of a BMI to control an ambulatory exoskeleton by patients with incomplete paraplegia(i.e., patients with good prognosis for gait rehabilitation).
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