Abstract
Background and purposePrevious tDCS studies in chronic stroke patients reported highly inconsistent effects on sensorimotor functions. Underlying reasons could be the selection of different kinematic parameters across studies and for different tDCS setups. We reasoned that tDCS may not simply induce global changes in a beneficial-adverse dichotomy, but rather that different sensorimotor kinematics are differentially affected. Furthermore, the often-postulated higher efficacy of bilateral-dual (bi-tDCS) over unilateral-anodal (ua-tDCS) could not yet be demonstrated consistently either. We investigated the effects of both setups on a wider range of kinematic parameters from standardized robotic tasks in patients with chronic stroke. MethodsTwenty-four patients with arm hemiparesis received tDCS (20min, 1 mA) concurrent to kinematic assessments in a sham-controlled, cross-over and double-blind clinical trial. Performance was measured on four sensorimotor tasks (reaching, proprioception, cooperative and independent bimanual coordination) from which 30 parameters were extracted. On the group-level, the patterns of changes relative to sham were assessed using paired-samples t-tests and classified as (1) performance increases, (2) decreases and (3) non-significant differences. Correlations between parametric change scores were calculated for each task to assess effects on the individual-level. ResultsBoth setups induced complex effect patterns with varying proportions of performance increases and decreases. On the group-level, more increases were induced in the reaching and coordination tasks while proprioception and bimanual cooperation were overall negatively affected. Bi-tDCS induced more performance increases and less decreases compared to ua-tDCS. Changes across parameters occurred more homogeneously under bi-tDCS than ua-tDCS, which induced a larger proportion of performance trade-offs. ConclusionsOur data demonstrate profound tDCS effects on sensorimotor functions post-stroke, lending support for more pronounced and favorable effects of bi-tDCS compared to ua-tDCS. However, no uniformly beneficial pattern was identified. Instead, the modulations varied depending on the task and electrode setup, with increases in certain parameters occurring at the expense of decreases in others.
Highlights
Background and purposePrevious Transcranial direct current stimulation (tDCS) studies in chronic stroke patients reported highly inconsistent effects on sensorimotor functions
Effects of bilateral tDCS (bi-tDCS) were more pronounced, as more parameters were significantly changed irrespective of change directionality, and more beneficial than uatDCS, as more performance increases (20% vs. 36.7%) and less decreases (40% vs. 33.3%) occurred (Fig. 5.A, Table 1 and Supplemental Table VI)
While larger proportions of increases were observed in Visually Guided Reaching (VGR) and independent bimanual coordination (IBC), both setups predominantly induced decreases in Arm Position Matching (APM) and cooperative bimanual coordination (CBC)
Summary
Previous tDCS studies in chronic stroke patients reported highly inconsistent effects on sensorimotor functions. We reasoned that tDCS may not induce global changes in a beneficial-adverse dichotomy, but rather that different sensorimotor kinematics are differentially affected. We investigated the effects of both setups on a wider range of kinematic parameters from standardized robotic tasks in patients with chronic stroke. On the group-level, the patterns of changes relative to sham were assessed using paired-samples t-tests and classified as (1) performance increases, (2) decreases and (3) non-significant differences. Results: Both setups induced complex effect patterns with varying proportions of performance increases and decreases. On the group-level, more increases were induced in the reaching and coordination tasks while proprioception and bimanual cooperation were overall negatively affected. The modulations varied depending on the task and electrode setup, with increases in certain parameters occurring at the expense of decreases in others
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