Anodal Transcranial Direct Current Stimulation Promotes Frontal Compensatory Mechanisms in Healthy Elderly Subjects

Cespón, Jesús; Rodella, Claudia; Rodella, Claudia; Rossini, Paolo M.; Miniussi, Carlo; Miniussi, Carlo; Pellicciari, Maria C. · 2017 · DOAJ

DOI: 10.3389/fnagi.2017.00420

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Summary

This study investigates whether transcranial direct current stimulation (tDCS) applied to the left dorsolateral prefrontal cortex (DLPFC) can modulate working memory performance and underlying neural activity in healthy young and elderly adults. Motivated by inconsistent findings in previous literature regarding tDCS efficacy and the need to understand the neural mechanisms of age-related cognitive decline, the researchers aimed to determine if anodal tDCS promotes frontal compensatory mechanisms in aging brains. The study specifically examined behavioral changes and electrophysiological correlates, focusing on the P300 event-related potential (ERP), which is associated with attentional resources and context updating. The experimental design involved 14 healthy young adults (mean age 24.8) and 14 healthy elderly adults (mean age 70.2). Participants underwent three separate sessions involving anodal, cathodal, or sham tDCS, counterbalanced across subjects. To equate task difficulty, young participants performed a 3-back working memory task, while elderly participants performed a 2-back task. Electroencephalogram (EEG) recordings were taken before and after stimulation. tDCS was delivered at 1.5 mA for 13 minutes, with the anode over the left DLPFC and the cathode over the right shoulder. Behavioral performance was assessed using reaction time and the d-prime index, while ERP analysis focused on frontal and parietal P300 amplitudes. Results indicated distinct age-dependent effects of tDCS. Young participants showed improved performance after sham stimulation, suggesting a practice effect, but this improvement was absent after anodal tDCS, implying that stimulation may have interfered with spontaneous learning in this group. In contrast, elderly participants showed significant improvements in accuracy (d-prime) only after anodal tDCS. Cathodal tDCS had no significant effect on either group. Electrophysiologically, anodal tDCS increased frontal P300 amplitude in elderly subjects, a change that was significantly correlated with their behavioral improvements. No such correlation was found in young participants. Additionally, while parietal P300 amplitudes increased after tDCS generally, these changes did not interact with group or stimulation type. The findings suggest that anodal tDCS over the left DLPFC enhances working memory in healthy elderly subjects by promoting frontal compensatory mechanisms. The correlation between increased frontal P300 amplitude and improved accuracy indicates that the stimulation facilitates the allocation of attentional resources, potentially offsetting age-related declines in posterior neural processing. This study highlights that tDCS effects are not uniform across age groups; while it may hinder learning in young adults who already possess efficient neural networks, it supports compensatory frontal recruitment in older adults, offering a potential non-pharmacological intervention for age-related cognitive decline.

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