Meta-analysis - tDCS on working memory performance
Transcranial direct current stimulation (tDCS) can temporarily change the activity of the brain. Consequently, several studies have tried to use tDCS to increase working memory performance in humans. Summarizing these studies in a meta-analysis can tell us if tDCS indeed consistently improves working memory.
However, there is one problem. All these studies use different tDCS electrode positions, orientations, and intensities. This leads to different brain regions being targeted. Therefore, throwing all studies in one analysis can be tricky. We developed a new method, relating working memory performance changes and electric fields related to tDCS.
From the 87 studies we investigated (69 in the left and 18 in the right frontal part of the brain), we retrieved how big their effects were. Next we used computational modeling to estimate where each study exactly stimulated. Then we related these two outcomes in a correlation measure. Finally, we performed a statistical test to see where correlations are significant.
Effect sizes on working memory
From our results one specific brain region came out as the area that, when stimulated with tDCS, most likely is related to improved working memory. This brain region was the lower part of the dorsolateral prefrontal cortex (see picture on the right). This region came out for the analysis on the left and the right side of the brain.
In this study we showed how summarized effect sizes and computational modeling of tDCS fields can be combined. Interestingly, many previous studies aimed to stimulate slightly different regions than we found in our analysis. The most targeted region is referred to as 'F3'. However, we found that it could be more optimal to stimulate a lower region, referred to as 'F5'. Thus, our results provide a potential way to increase effects of tDCS on working memory. But, keep in mind, we used a modeling approach. That means that our results need to be verified by experimental studies.
Wischnewski, Mantell & Opitz (2021). Identifying regions in prefrontal cortex related to working memory improvement: a novel meta-analytic method using electric field modeling. BioRxiv pre-print. https://doi.org/10.1101/2021.03.11.435002