Enhancing Locomotor Learning With Transcutaneous Spinal Electrical Stimulation and Somatosensory Augmentation: A Pilot Randomized Controlled Trial in Older Adults

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.

Assessing adverse effects and unspecific effects of transcutaneous spinal direct current stimulation (tsDCS)

“…We also asked participants about the onset, duration, and location of experienced AEs and observed that there were temporally more-extended AE reports as well as more reports of sensations under both electrodes in the active conditions. While previous tsDCS studies mostly focused on the presence or absence of AEs [29, 31], we believe that a spatio-temporal characterization of AEs as carried out here is important for allowing to design an appropriate tsDCS control condition that ensures adequate blinding.…”

“…This allowed us to provide detailed descriptions of overall AE reports as well as condition-differences using Frequentist and Bayesian statistics, including spatio-temporal AE aspects and blinding success. To our knowledge, this combination of factors goes far beyond what has previously been carried out in the tsDCS literature: out of 76 human tsDCS studies, only nine [24][25][26][27][28][29][30][31][32] employed structured questionnaires, with only three of these statistically comparing effects under active and sham conditions [25,28,29] and none investigating spatio-temporal aspects. Our study thus provides a starting point for a systematic and comprehensive assessment of tsDCS AEs, and we believe that the tsDCS community might benefit from a standardized and psychometrically evaluated questionnaire.…”

“…An AE assessment based on questionnaires was only carried out in 9 studies and the level of reported details was rather limited (Table 2). A keyword search for UE reporting revealed hits in 10 studies [7,[26][27][28][29][30][31][32][33][34], but with the exception of one study [23] (which assessed polarity-dependent changes in spontaneous breathing patterns) none obtained tsDCS-concurrent recordings without potential confounds, i.e., the relevant measures were primarily used as an indicator to ensure adequate task performance. "Participants' reports on verbal 0/10 scales indicated the following.…”

What Else Can Be Done by the Spinal Cord? A Review on the Effectiveness of Transpinal Direct Current Stimulation (tsDCS) in Stroke Recovery

“…As shown in Table 2 , the effects of tsDCS on motor improvement in humans were identified in 10 out of 17 studies. Most studies targeted the thoracic vertebrae (T-11-T12; [ 45 , 46 , 47 , 48 , 49 , 50 , 52 , 53 ] (but see [ 51 , 54 ]) showing that anodal tsDCS can be effective in preventing fatigue and in enhancing different whole-body movements [ 45 , 48 ]. It can also improve sleep and restless leg symptoms (RLSs) in idiopathic RLS subjects [ 50 ].…”

“…It can also improve sleep and restless leg symptoms (RLSs) in idiopathic RLS subjects [ 50 ]. In Clark et al’s study [ 52 ], thirty minutes of anodal tsDCS combined with a complex terrain motor task determined larger and more consistent retention of performance than the sham condition.…”