Theta band high definition transcranial alternating current stimulation, but not transcranial direct current stimulation, improves associative memory performance

Stefan Lang,Oury Monchi,Tazrina Alrazi,Liu Shi Gan

doi:10.1038/s41598-019-44680-8

Abstract

Associative memory (AM) deficits are common in neurodegenerative disease and novel therapies aimed at improving these faculties are needed. Theta band oscillations within AM networks have been shown to be important for successful memory encoding and modulating these rhythms represents a promising strategy for cognitive enhancement. Transcranial alternating current stimulation (TACS) has been hypothesized to entrain and increase power of endogenous brain rhythms. For this reason, we hypothesized that focal delivery of theta band electrical current, using high-definition TACS, would result in improved AM performance compared to sham stimulation or transcranial direct current stimulation (TDCS). In this pilot study, 60 healthy subjects were randomized to receive high definition TACS, high definition TDCS, or sham stimulation delivered to the right fusiform cortex during encoding of visual associations. Consistent with our hypothesis, improved AM performance was observed in the TACS group, while TDCS had no effect. However, TACS also resulted in improved correct rejection of never seen items, reduced false memory, and reduced forgetting, suggesting the effect may not be specific for AM processes. Overall, this work informs strategies for improving associative memory and suggests alternating current is more effective than direct current stimulation in some contexts.

Highlights

IntroductionMemory for the relationship or association between two items (associative memory; Associative memory (AM)) is critical for normal everyday functioning
Memory for the relationship or association between two items is critical for normal everyday functioning
Post-hoc testing demonstrated this resulted from subjects receiving Transcranial alternating current stimulation (TACS) reporting higher ratings than Sham (U = 450, p = 0.017)

Summary

Introduction

Memory for the relationship or association between two items (associative memory; AM) is critical for normal everyday functioning. In a large meta-analysis examining neural regions involved in the subsequent memory effect of verbal and non-verbal(visual) information, it was found that the fusiform cortex was preferentially involved in the encoding of successful visual associative memory[4]. Stimulation using 1 × 1 TDCS applied to the left dorsolateral prefrontal cortex (DLPFC)[25,26] or left inferior frontal gyrus (IFG)[27] during encoding of a face-name task improved memory performance. These positive results are contrasted by the findings of Gaynor et al.[28] and Leach et al.[29].

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Results

Conclusion