Effects of Transcranial Direct Current Stimulation Paired With Cognitive Training on Functional Connectivity of the Working Memory Network in Older Adults

Nicole R Nissim, Andrew O'Shea, Aprinda Indahlastari, Jessica N Kraft, Olivia von Mering, Serkan Aksu, Eric Porges, Ronald Cohen, Adam J Woods, Nicole R Nissim, Andrew O'Shea, Aprinda Indahlastari, Jessica N Kraft, Olivia von Mering, Serkan Aksu, Eric Porges, Ronald Cohen, Adam J Woods

Abstract

Background: Working memory, a fundamental short-term cognitive process, is known to decline with advanced age even in healthy older adults. Normal age-related declines in working memory can cause loss of independence and decreased quality of life. Cognitive training has shown some potential at enhancing certain cognitive processes, although, enhancements are variable. Transcranial direct current stimulation (tDCS), a form of non-invasive brain stimulation, has shown promise at enhancing working memory abilities, and may further the benefits from cognitive training interventions. However, the neural mechanisms underlying tDCS brain-based enhancements remain unknown.

Objective/hypothesis: Assess the effects of a 2-week intervention of active-tDCS vs. sham paired with cognitive training on functional connectivity of the working memory network during an N-Back working memory task.

Methods: Healthy older adults (N = 28; mean age = 74 ± 7.3) completed 10-sessions of cognitive training paired with active or sham-tDCS. Functional connectivity was evaluated at baseline and post-intervention during an N-Back task (2-Back vs. 0-Back).

Results: Active-tDCS vs. sham demonstrated a significant increase in connectivity between the left dorsolateral prefrontal cortex and right inferior parietal lobule at post-intervention during 2-Back. Target accuracy on 2-Back was significantly improved for active vs. sham at post-intervention.

Conclusion: These results suggest pairing tDCS with cognitive training enhances functional connectivity and working memory performance in older adults, and thus may hold promise as a method for remediating age-related cognitive decline. Future studies evaluating optimal dose and long-term effects of tDCS on brain function will help to maximize potential clinical impacts of tDCS paired with cognitive training in older adults.

Clinical trial registration: www.ClinicalTrials.gov, identifier NCT02137122.

Keywords: N-Back; cognitive aging; cognitive training; fMRI; functional connectivity; neuromodulation; transcranial direct current stimulation; working memory.

Copyright © 2019 Nissim, O’Shea, Indahlastari, Kraft, von Mering, Aksu, Porges, Cohen and Woods.

Figures

FIGURE 1
FIGURE 1
Experimental design and study timeline.
FIGURE 2
FIGURE 2
A computational model of electric field distribution for F3–F4 placement in one participant. The left hand side depicts the electric field strengths (|EF|) on the cortical surface for F3 (cathode, blue electrode) and F4 (anode, red electrode) montage. |EF| distribution was calculated using a finite element based approach in ROAST (Huang et al., 2019).
FIGURE 3
FIGURE 3
Example of a 2-Back working memory task.
FIGURE 4
FIGURE 4
Mean functional connectivity β values (±standard error) for 2-Back over rest at baseline and post-intervention from left dorsolateral prefrontal cortex (DLPFC) to right inferior parietal cortex (IPL), ∗p-FDR < 0.05 (LH = left hemisphere; RH = right hemisphere).
FIGURE 5
FIGURE 5
Seed to target ROIs with significantly increased connectivity during the 2-Back task at post-intervention (ROI colors: Red = left DLPFC; Black = right IPL).
FIGURE 6
FIGURE 6
Mean percent accuracy for 2-Back target stimuli. Error bars represent standard error of the mean (∗p < 0.05).
FIGURE 7
FIGURE 7
Reaction time on 2-Back target stimuli reported in milliseconds (ms) from baseline to post-intervention. Error bars represent standard error of the mean.

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