Non-Invasive Brain Stimulation and the Enhancement of Working Memory

Abstract

Memory is an essential cognitive process that is crucial for day to day tasks. Specifically, working memory allows for the processing and manipulation of information. Baddeley and Hitch’s (1974) model of working memory (WM) has been widely accepted and is the basis for many working memory studies. However, this parsimonious model is limited, especially in its ability to distinguish between verbal and tonal information. Furthermore, another debated area of cognitive research is the use of transcranial current stimulation, specifically transcranial direct current stimulation (tDCS), as a cognition enhancer. The present study seeks to address three questions: (1) is there a separate working memory system for music distinct from verbal working memory, (2) in the context of verbal and musical working memory, can tDCS be used to enhance one or both of these types of memory, and (3) can tDCS be used to enhance musical and/or verbal long-term memory, and (4) is there a difference in long-term memory (LTM) confidence judgements between verbal and musical working memory. Participants (N = 72) completed a verbal 2-back task, a tonal 2-back task, and an LTM test in which memory for stimuli presented in the WM tasks was tested and confidence was assessed. Participants were randomly assigned to three tDCS conditions: no stimulation, sham, or stimulation. Stimulation occurred for twenty minutes over the left supramarginal gyrus and then participants completed both WM tasks and a LTM assessment. This study failed to find enhancing effects of tDCS on WM or LTM performance when compared to control conditions. Verbal WM task accuracy was higher than the musical WM task, musical LTM was higher than verbal LTM. Participants were more confident on musical stimuli judgments compared to verbal stimuli in the LTM test. This study found mixed results on tDCS’s effect on memory.