Anodal Transcranial Direct Current Stimulation Over S1 Differentially Modulates Proprioceptive Accuracy in Young and Old Adults

Abstract

Background: 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. Objective: This study investigated online effects of a-tDCS over S1 on proprioceptive accuracy in young (YA) and old healthy adults (OA). Methods: The 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. Results: a-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. Conclusion: a-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.

Age-related differences of motor cortex plasticity in adults: A transcranial direct current stimulation study

“…Despite promising findings in these pilot studies, results of other studies are at least partially heterogeneous. Anodal tDCS applied over the primary somatosensory cortex, which enhanced performance of proprioceptive accuracy in a young subject group, reduced performance in elderly participants [98], and prefrontal anodal tDCS did not change working memory performance in older adults in another study [99]. The results of the present study would suggest that these negative results might be caused by the reduced efficacy of tDCS in higher age, and thus it might be required to adapt stimulation protocols including intensity, duration, and repetition rate [47,48,100e105].…”

Does participant’s age impact on tDCS induced fields? Insights from computational simulations

“…For example, using grouped ages, higher peak fields have been revealed in children, declining in adolescence and adulthood [37,38]. This is in addition to findings of higher peak fields in young compared to older adults [38,74]. Furthermore, a slight negative correlation for peak electric fields was displayed between the ages 21 and 55 [75].…”

Anodal Transcranial Direct Current Stimulation Over Prefrontal Cortex Slows Sequence Learning in Older Adults

“…However, the older adult participants who received stimulation during practice no longer had a motor performance deficit. While the findings from these studies suggest that tDCS may improve motor learning for older adults, other studies show either no benefit or even poorer performance when tDCS is paired with task practice (Mooney et al, 2019;Muffel et al, 2019;Habich et al, 2020;Chow et al, 2021). For example, one study found no benefit of a single session of anodal M1 tDCS as older and young adult participants learned a sequential isometric force task using their non-dominant hand during practice (Mooney et al, 2019).…”