Modulating Phonological Short-Term Memory in Stroke Survivors With Aphasia Using Transcranial Alternating Current Stimulation

Abstract

Background

Short-term maintenance of phonological information is critical for language production and comprehension, and is often impaired in stroke survivors with aphasia.

Objective

In this pilot study, we investigated whether brain oscillatory activity underlying phonological short-term memory (pSTM) can be influenced by transcranial alternating current stimulation (tACS) in stroke survivors with aphasia (SWA).

Methods

In a within-subject, single-blinded, sham-controlled study, 13 SWA received theta-tACS (4-7 Hz) targeting left temporoparietal and inferior frontal regions across 3 tACS conditions (in-phase, anti-phase, and sham; 20 minutes each). Participants completed an adaptive delayed match-to-sample task with spoken consonant-vowel strings (2-8 syllables) before, during, and after stimulation. The primary outcome was change in pSTM capacity (ie, number of syllables maintained over a 5-second delay), estimated using a linear interpolation approach. We hypothesized that in-phase tACS would enhance, and anti-phase tACS would disrupt, pSTM capacity relative to sham.

Results

LME analyses reveal significant interactions between tACS condition and block (F(4, 91.9) = 2.65, P = .038), and post-hoc estimated marginal means comparisons show increased pSTM capacity during in-phase tACS versus sham (estimate = 0.71, t(92) = 2.26, P = .040) and anti-phase (estimate = 0.75, t(92) = 2.44, P = .040) conditions, only during the stimulation period. Differences between anti-phase and sham-tACS were not significant (estimate = −0.04, P = .901). Individual response to tACS was variable, with only 60% of SWA responding.

Conclusions

This study supports in-phase theta-tACS positively impacts pSTM. Larger studies are needed to confirm these findings and evaluate lasting effects to increase clinical relevance.