Impact of Non-invasive Brain Stimulation on Learning Novel Spoken Words

The purpose of the proposed study is to use transcranial magnetic stimulation (TMS) to evaluate a neurobiological model of spoken word learning in older youth. Specifically, it is hypothesized that: (1) inhibition of the left dorsal stream will impact subsequent learning, processing, and retention of phonologically similar pseudowords; (2) the impact of dorsal stream inhibition on word learning will be associated with baseline levels of variability in neural activity, indicative of underlying differences in cortical excitability.

The proposed study is designed to assess the contribution of the dorsal stream of the language network (i.e., left supramarginal gyrus, or SMG) to different aspects of novel word learning in two groups of participants (16-24 years of age): 20 typically developing older youth (OYTD; tested in Aim 1) and 20 older youth with reading difficulties (OYRD; tested in Aim 2). The investigators will use inhibitory continuous theta burst stimulation (cTBS), a well-established repetitive TMS (rTMS) protocol that reduces cortical excitability in a targeted brain region for up to 60 minutes. Participants will complete a baseline magnetic resonance imaging (MRI) session in Week 1, followed by cTBS or sham stimulation to the left SMG, with order of administration counterbalanced across participants. Immediately following cTBS (or sham), participants will complete a visual pseudoword phonological discrimination task and a spoken word learning task. The following day (i.e., 24 hours later), retention of items learned will be measured. In Week 2, cTBS (or sham) will be administered to the left SMG (whichever stimulation was not administered in Week 1) and then the pseudoword discrimination and word learning tasks will be administered using a different set of novel words from those presented in Week 1. Twenty-four hours later, the retention of this second set of items will be measured.