Abstract
The effects of transcranial direct current stimulation (tDCS) on working memory (WM) performance are promising but variable and contested. In particular, designs involving one session of tDCS are prone to variable outcomes with notable effects of individual differences. Some participants benefit, whereas others are impaired by the same tDCS protocol. In contrast, protocols including multiple sessions of tDCS more consistently report WM improvement across participants. The objective of the current project was to test whether differences in resting-state connectivity between stimulation site and two WM-relevant networks [default mode network (DMN) and central executive network (CEN)] could account for initial and longitudinal responses to tDCS. Healthy young adults completed 5 days of visual WM training during sham or anodal right frontal tDCS. The behavioral data showed that only the active tDCS group significantly improved over the visual WM training period. There were no significant correlations between initial response to tDCS and resting-state activity. DMN activity in the anterior cingulate cortex significantly correlated with WM training slope. These data underscore the importance of sampling in studies applying tDCS; homogeneity (e.g., of gender, special population, and WM capacity) may produce more consistent data in a single experiment with limited power, whereas heterogeneity is important in determining the mechanism(s) and potential for tDCS-linked protocols. This issue is a limitation in tDCS findings that continues to hamper its optimization and translational value.
Highlights
Neurostimulation offers hope as a way to improve capacity-limited working memory (WM; Cowan, 2001) and its age-related decline (Reuter-Lorenz and Park, 2010)
We previously reported that transcranial direct current stimulation (tDCS) effects interacted with individual differences based on participants’ WM capacity (Jones and Berryhill, 2012; Gözenman and Berryhill, 2016; Arciniega et al, 2018), level of educational attainment (Berryhill and Jones, 2012), and even level of motivation (Jones et al, 2015a)
Resting-State fMRI Does Predict Longitudinal tDCS Response (Training Slope) In the active tDCS group, we investigated whether resting-state fMRI (rsfMRI) predicted WM performance across tDCS-linked WM training
Summary
Neurostimulation offers hope as a way to improve capacity-limited working memory (WM; Cowan, 2001) and its age-related decline (Reuter-Lorenz and Park, 2010). When WM benefits are found, the underlying mechanism appears to be enhanced frontoparietal connectivity (McNab and Klingberg, 2008; Constantinidis and Klingberg, 2016; Chen et al, 2019). Some evidence shows that one session of tDCS can improve WM performance in healthy (Sandrini et al, 2012; Brunoni and Vanderhasselt, 2014; Trumbo et al, 2016; Brunye et al, 2017), and patient populations (Boggio et al, 2006; Jo et al, 2009; Saunders et al, 2015; Wu et al, 2016), reviewed in Berryhill and Martin (2018). The jury remains split as several reviews, and metaanalyses provide differing conclusions, suggesting that there are few cognitive benefits associated with tDCS (Horvath et al, 2015), that meta-analyses minimizing tDCS-effects are flawed (Antal et al, 2015), or that there are benefits under certain conditions, such as longitudinal designs (Brunoni and Vanderhasselt, 2014; Elmasry et al, 2015; Hill et al, 2016; Jantz et al, 2016; Mancuso et al, 2016)
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