Abstract
BackgroundProprioception is a prerequisite for successful motor control but declines throughout the lifespan. Brain stimulation techniques such as anodal transcranial direct current stimulation (a-tDCS) are capable of enhancing sensorimotor performance across different tasks and age groups. Despite such growing evidence for a restorative potential of tDCS, its impact on proprioceptive accuracy has not been studied in detail yet.ObjectiveThis study investigated online effects of a-tDCS over S1 on proprioceptive accuracy in young (YA) and old healthy adults (OA).MethodsThe effect of 15 min of a-tDCS vs. sham on proprioceptive accuracy was assessed in a cross-over, double blind experiment in both age groups. Performance changes were tested using an arm position matching task in a robotic environment. Electrical field (EF) strengths in the target area S1 and control areas were assessed based on individualized simulations.Resultsa-tDCS elicited differential changes in proprioceptive accuracy and EF strengths in the two groups: while YA showed a slight improvement, OA exhibited a decrease in performance during a-tDCS. Stronger EF were induced in target S1 and control areas in the YA group. However, no relationship between EF strength and performance change was found.Conclusiona-tDCS over S1 elicits opposing effects on proprioceptive accuracy as a function of age, a result that is important for future studies investigating the restorative potential of a-tDCS in healthy aging and in the rehabilitation of neurological diseases that occur at advanced age. Modeling approaches could help elucidate the relationship between tDCS protocols, brain structure and performance modulation.
Highlights
Proprioception – the perception of body position and movement – is a vital function for daily activities including postural stability and reaching movements (Findlater et al, 2016), which declines in the course of aging (Stelmach and Sirica, 1986; Adamo et al, 2007; Herter et al, 2014; Hughes et al, 2015)
Interaction Effect A differential effect of anodal transcranial direct current stimulation (a-transcranial direct current stimulation (tDCS)) on performance was demonstrated by a significant interaction between age group and stimulation condition for all four outcome parameters (EAE: F(1, 43) = 5.22, p = 0.027, η2 = 0.11; shoulder angle error (SAE): F(1, 43) = 5.07, p = 0.029, η2 = 0.11; variability of the elbow angle error (VEAE): F(1, 43) = 6.77, p = 0.013, η2 = 0.14; variability of the shoulder angle error (VSAE): F(1, 43) = 6.79, p = 0.013, η2 = 0.14), with young adult group (YA) exhibiting slight reductions in elbow angle error (EAE) and SAE whereas old adult group (OA) showed marked increases through stimulation
Age groups diverged significantly in performance (EAE: t(36.8) = 2.687, p = 0.011; SAE: t(43) = 2.498, p = 0.016): while YA slightly improved under a-tDCS, the performance of the OA decreased
Summary
Proprioception is a prerequisite for successful motor control but declines throughout the lifespan. Brain stimulation techniques such as anodal transcranial direct current stimulation (a-tDCS) are capable of enhancing sensorimotor performance across different tasks and age groups. Despite such growing evidence for a restorative potential of tDCS, its impact on proprioceptive accuracy has not been studied in detail yet
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