Enhancing Working Memory Training with Transcranial Direct Current Stimulation

Abstract

Working memory (WM) is a fundamental cognitive ability that supports complex thought but is limited in capacity. Thus, WM training interventions have become very popular as a means of potentially improving WM-related skills. Another promising intervention that has gained increasing traction in recent years is transcranial direct current stimulation (tDCS), a noninvasive form of brain stimulation that can modulate cortical excitability and temporarily increase brain plasticity. As such, it has the potential to boost learning and enhance performance on cognitive tasks. This study assessed the efficacy of tDCS to supplement WM training. Sixty-two participants were randomized to receive either right prefrontal, left prefrontal, or sham stimulation with concurrent visuospatial WM training over the course of seven training sessions. Results showed that tDCS enhanced training performance, which was strikingly preserved several months after training completion. Furthermore, we observed stronger effects when tDCS was spaced over a weekend break relative to consecutive daily training, and we also demonstrated selective transfer in the right prefrontal group to nontrained tasks of visual and spatial WM. These findings shed light on how tDCS may be leveraged as a tool to enhance performance on WM-intensive learning tasks.

Optimizing Transcranial Direct Current Stimulation Protocols to Promote Long-Term Learning

“…Prichard et al 2014). Furthermore, our previous work in the cognitive domain (Au et al 2016) showed similar effects using a WM intervention combined with online tDCS. As with motor skill, we also observed a higher rate of learning in our stimulated group, relative to sham.…”

“…Moreover, our own work demonstrated with a WM intervention that participants showed the greatest improvement after a weekend break (Au et al 2016), suggesting in addition to the meta-plasticity protocols that longer spacing intervals of several days can actually be beneficial for consolidation as well. How do we reconcile these disparate results?…”

“…Despite the evidence in support of short, within-day spacing intervals, a number of successful intervention studies have been carried out using a once-daily approach (e.g., Alonzo et al 2012;Au et al 2016;Reis et al 2015;Reis et al 2009;Stephens and Berryhill 2016). Moreover, our own work demonstrated with a WM intervention that participants showed the greatest improvement after a weekend break (Au et al 2016), suggesting in addition to the meta-plasticity protocols that longer spacing intervals of several days can actually be beneficial for consolidation as well.…”

Individual Differences and Long-term Consequences of tDCS-augmented Cognitive Training

“…A recent meta-analysis from Mancuso, Ilieva, Hamilton, and Farah (2016) suggests that dorsolateral pFC (DLPFC) stimulation during training results in a small but significant enhancement effect, which survives corrections for publication bias. Recent research from our own laboratory (Au et al, 2016) provides further evidence that DLPFC stimulation (both right and left) enhances performance on a widely used n-back training task over the course of seven sessions, relative to a sham stimulation condition. Although these initial findings do provide some preliminary support for the use of tDCS to enhance learning of WM-intensive tasks, we note considerable heterogeneity in the literature.…”

“…For example, a similarly designed n-back/ tDCS training study failed to find an effect of tDCS after correcting for baseline differences (Martin et al, 2013), and the 10 tDCS/ WM training studies covered in the Mancuso et al (2016) meta-analysis differ substantially in the magnitude of their effects, with Hedges' g values ranging from 0.074 to 0.565. A variety of factors, including differences in stimulation intensity, density, location, and other parameters, as well as the design and implementation of the cognitive training paradigm, may explain the disparities in the strength of these effects (see Au et al, 2016, for a brief discussion). However, one additional possibility is that individual differences among participants-including motivation, sex, and baseline ability, among many factors-may play important roles.…”