Abstract
This study investigated locomotor learning of a complex terrain walking task in older adults, when combined with two adjuvant interventions: transcutaneous spinal direct current stimulation (tsDCS) to increase lumbar spinal cord excitability, and textured shoe insoles to increase somatosensory feedback to the spinal cord. The spinal cord has a crucial contribution to control of walking, and is a novel therapeutic target for rehabilitation of older adults. The complex terrain task involved walking a 10-meter course consisting of nine obstacles and three sections of compliant (soft) walking surface. Twenty-three participants were randomly assigned to one of the following groups: sham tsDCS and smooth insoles (sham/smooth; control group), sham tsDCS and textured insoles (sham/textured), active tsDCS and smooth insoles (active/smooth), and active tsDCS and textured insoles (active/textured). The first objective was to assess the feasibility, tolerability, and safety of the interventions. The second objective was to assess preliminary efficacy for increasing locomotor learning, as defined by retention of gains in walking speed between a baseline visit of task practice, and a subsequent follow-up visit. Variability of the center of mass while walking over the course was also evaluated. The change in executive control of walking (prefrontal cortical activity) between the baseline and follow-up visits was measured with functional near infrared spectroscopy. The study results demonstrated feasibility based on enrollment and retention of participants, tolerability based on self-report, and safety based on absence of adverse events. Preliminary efficacy was supported based on trends showing larger gains in walking speed and more pronounced reductions in mediolateral center of mass variability at the follow-up visit in the groups randomized to active tsDCS or textured insoles. These data justify future larger studies to further assess dosing and efficacy of these intervention approaches. In conclusion, rehabilitation interventions that target spinal control of walking present a potential opportunity for enhancing walking function in older adults.
Highlights
Physical rehabilitation is the most effective approach for restoring or preserving walking function in older adults (Buford et al, 2014)
This study investigated learning of a complex terrain walking task when combined with two adjuvant interventions targeting spinal control: transcutaneous spinal direct current stimulation and textured shoe insoles. tsDCS is a non-invasive neuromodulation approach that applies a weak electrical current to the spinal cord via electrodes placed on the skin
The first goal was to assess the feasibility, tolerability, and safety of tsDCS and textured shoe insoles when combined with a complex terrain walking task in older adults
Summary
Physical rehabilitation is the most effective approach for restoring or preserving walking function in older adults (Buford et al, 2014). Somatosensory information elicits reflex responses to unexpected perturbations (e.g., striking an obstacle) (Zehr and Stein, 1999) During complex tasks such as walking over uneven terrain or stepping over an obstacle, the spinal cord integrates descending motor commands with ongoing CPG activity to transiently adjust gait mechanics (Michel et al, 2007; Haefeli et al, 2011). This study investigated learning of a complex terrain walking task when combined with two adjuvant interventions targeting spinal control: transcutaneous spinal direct current stimulation (tsDCS) and textured shoe insoles. The long term objective of this line of research is to test whether intervention adjuvants that target spinal circuits may improve locomotor learning of a complex terrain walking task For this particular study, the first goal was to assess the feasibility (participant enrollment and drop-out), tolerability (occurrence and severity of side effects), and safety (adverse events) of tsDCS and textured shoe insoles when combined with a complex terrain walking task in older adults. The study had two hypotheses: (1) the interventions would be safe and welltolerated by participants, and (2) compared to a control group with smooth insoles and sham tsDCS, effect sizes would support better retention of task performance in the groups who received active tsDCS, or textured insoles, or a combination of both
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