Abstract
Working memory (WM) permits maintenance of information over brief delays and is an essential executive function. Unfortunately, WM is subject to age-related decline. Some evidence supports the use of transcranial direct current stimulation (tDCS) to improve visual WM. A gap in knowledge is an understanding of the mechanism characterizing these tDCS linked effects. To address this gap, we compared the effects of two tDCS montages designed on visual working memory (VWM) performance. The bifrontal montage was designed to stimulate the heightened bilateral frontal activity observed in aging adults. The unilateral frontoparietal montage was designed to stimulate activation patterns observed in young adults. Participants completed three sessions (bilateral frontal, right frontoparietal, sham) of anodal tDCS (20 min, 2 mA). During stimulation, participants performed a visual long-term memory (LTM) control task and a visual WM task. There was no effect of tDCS on the LTM task. Participants receiving right unilateral tDCS showed a WM benefit. This pattern was most robust in older adults with low WM capacity. To address the concern that the key difference between the two tDCS montages could be tDCS over the posterior parietal cortex (PPC), we included new analyses from a previous study applying tDCS targeting the PPC paired with a recognition VWM task. No significant main effects were found. A subsequent experiment in young adults found no significant effect of either tDCS montage on either task. These data indicate that tDCS montage, age and WM capacity should be considered when designing tDCS protocols. We interpret these findings as suggestive that protocols designed to restore more youthful patterns of brain activity are superior to those that compensate for age-related changes.
Highlights
Visual working memory (VWM) allows us to integrate perception across interruptions such as eye movements
To test whether the transcranial direct current stimulation (tDCS) montages differentially modulated VWM performance, Difference Index (DI) were subjected to mixed effects analysis of variance (ANOVA) with the within-subjects factors of montage and set size (3, 6), and the between subject factor of VWM capacity; see Figure 3
We initiated the current experiments to test whether healthy older adults would receive greater VWM benefit from a frontoparietal tDCS montage that was hypothesized to restore a more lateralized pattern of VWM-related brain activity, or from a bifrontal montage hypothesized to support compensatory bilateral frontal activity
Summary
Visual working memory (VWM) allows us to integrate perception across interruptions such as eye movements. The PASA pattern generalizes across a range of cognitive functions including attention (Madden et al, 2002; Cabeza et al, 2004; Ansado et al, 2012), visual perception (Grady, 1996, 2000; Iidaka et al, 2002; Ansado et al, 2012), visuospatial processing (Nyberg et al, 2003; Meulenbroek et al, 2004; Ansaldo et al, 2015), VWM (D’Esposito et al, 2000; Grossman et al, 2002; Dennis and Peterson, 2012; Jockwitz et al, 2017), and episodic memory (Anderson et al, 2000; Cabeza et al, 2004; Gutchess et al, 2005; Dennis and Peterson, 2012). In studies comparing the functional activation patterns of young and old adults a more lateralized, unilateral pattern becomes more bilateral and frontal with age
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