Modulating Phonological Working Memory With Anodal High-Definition Transcranial Direct Current Stimulation to the Anterior Portion of the Supplementary Motor Area.

Abstract

Phonological working memory is key to vocabulary acquisition, spoken word recognition, real-time language processing, and reading. Transcranial direct current stimulation, when coupled with behavioral training, has been shown to facilitate speech motor output processes, a key component of nonword repetition, the primary task used to assess phonological working memory. In this study, we examined the efficacy of combining overt nonword repetition training with anodal high-definition transcranial direct current stimulation (HD tDCS) to the presupplementary motor area (preSMA) to enhance nonword repetition. This study investigated whether 20 min of active or sham anodal HD tDCS targeting preSMA concurrently with a nonword repetition task differentially impacted nonword repetition ability. Twenty-eight neurotypical college-age adults (18-25 years; 19 females, eight males, one nonbinary) completed a 20-min nonword repetition training task where they received either active or sham 1-mA anodal HD tDCS to the preSMA while overtly repeating a list of four-, five-, six-, and seven-syllable English-like nonwords presented in a random order. Whole nonword accuracy and error patterns (phoneme and syllable) were measured prior to and following training. Following training, both groups showed a decrease in nonword repetition accuracy. The drop in performance was significantly greater for the active stimulation group compared to the sham stimulation group at the four-syllable nonword length. The findings suggest that targeting the speech motor component of nonword repetition through overt training and HD tDCS to the preSMA does not enhance phonological working memory ability.