Working Memory Training Coupled With Transcranial Direct Current Stimulation in Older Adults: A Randomized Controlled Experiment

Abstract

BackgroundTranscranial direct current stimulation (tDCS) has been employed to boost working memory training (WMT) effects. Nevertheless, there is limited evidence on the efficacy of this combination in older adults. The present study is aimed to assess the delayed transfer effects of tDCS coupled with WMT in older adults in a 15-day follow-up. We explored if general cognitive ability, age, and educational level predicted the effects.MethodsIn this single-center, double-blind randomized sham-controlled experiment, 54 older adults were randomized into three groups: anodal-tDCS (atDCS)+WMT, sham-tDCS (stDCS)+WMT, and double-sham. Five sessions of tDCS (2 mA) were applied over the left dorsolateral prefrontal cortex (DLPFC). Far transfer was measured by Raven’s Advanced Progressive Matrices (RAPM), while the near transfer effects were assessed through Digit Span. A frequentist linear mixed model (LMM) was complemented by a Bayesian approach in data analysis.ResultsWorking memory training improved dual n-back performance in both groups submitted to this intervention but only the group that received atDCS+WMT displayed a significant improvement from pretest to follow-up in transfer measures of reasoning (RAPM) and short-term memory (forward Digit Span). Near transfer improvements predicted gains in far transfer, demonstrating that the far transfer is due to an improvement in the trained construct of working memory. Age, formal education, and vocabulary score seem to predict the gains in reasoning. However, Bayesian results do not provide substantial evidence to support this claim.ConclusionThis study will help to consolidate the incipient but auspicious field of cognitive training coupled with tDCS in healthy older adults. Our findings demonstrated that atDCS may potentialize WMT by promoting transfer effects in short-term memory and reasoning in older adults, which are observed especially at follow-up.

Long-term effects of repeated multitarget high-definition transcranial direct current stimulation combined with cognitive training on response inhibition gains

“…Although the 2-back accuracy δ values of the stimulation condition were higher than those of the combined protocol, this was attributed to the baseline difference between the two conditions. Since the 2-back accuracy of the combined protocol was significantly higher than the stimulation condition, it had less room for improvement ( Shaw and Hosseini, 2021 ; Teixeira-Santos et al, 2022 ). Therefore, the difference was unrelated to the interventions.…”

“…However, the combined condition not only enhanced the LP subgroup performance but also improved the HP subgroup performance at the follow-up session compared to the stimulation-alone condition, which only enhanced the response inhibition of the LP subgroup. According to the compensation hypothesis ( Shaw and Hosseini, 2021 ; Teixeira-Santos et al, 2022 ), the effects of cognitive enhancement techniques, such as tDCS and cognitive training, depend on baseline performance, and individuals with high baseline performance are difficult to be enhanced because they may already be near the peak level of cognitive ability. Therefore, there is less room for improvement.…”

The MEDITAGING study: protocol of a two-armed randomized controlled study to compare the effects of the mindfulness-based stress reduction program against a health promotion program in older migrants in Luxembourg

“…According to our eligibility criteria (see Table 1 ), participants have no major neurological or psychiatric disorders or current unstable illness. Moreover, as we previously verified that Portuguese older adults often present symptoms of anxiety, depression, pain, and sleep disorders [ 46 , 47 ], we opted for broader inclusion criteria to maximize ecological validity. Additionally, we believe that participants presenting these symptoms would most likely benefit from the interventions [ 48 ].…”

Lasting enhancements in neural efficiency by multi-session transcranial direct current stimulation during working memory training

“…As a cognitive enhancement technique, transcranial direct current stimulation (tDCS) has been extensively studied over the past two decades, demonstrating its ability to improve working memory (WM) in both healthy and cognitively impaired subjects based on its ability to modulate neuronal excitability and plasticity [1][2][3] . Significant benefits of tDCS have been demonstrated by evidence that the performance benefits of the combination of tDCS and multi-day WM training (WMT) can persist over the long term, i.e., from one month to almost one year after the end of training [4][5][6][7][8][9][10][11][12][13] , and that these benefits have the potential to transfer to other untrained WM tasks 7,8,12,[14][15][16] , fluid intelligence 17 and even everyday tasks 9 . However, quantifying the effectiveness of tDCS +WMT in most previous studies has focused only on behavioral measures such as accuracy or reaction time (RT), which can provide a general but superficial understanding of cognitive effects.…”