Slide Slam P5 Sandbox Series
Effects of transcranial alternating current stimulation (tACS) on language and network coherence in aphasia
Lynsey Keator1, Lisa Johnson2, Lorelei Johnson3, Julius Fridriksson4; 1University of South Carolina
Background Approximately 20-35 percent of stroke survivors experience aphasia, a language disorder resulting from damage to language regions of the left hemisphere (LH). Nonfluent aphasia (NFA) is one of the most common subtypes of aphasia, a language disorder resulting from damage to language regions in the left hemisphere (LH). NFA is particularly resistant to treatment, with nonfluent speech being one of the most refractory symptoms. A treatment paradigm called speech entrainment (SE), established by our group facilitates fluent speech production in NFA (Fridriksson et al., 2012; 2015) and improves anterior-posterior LH functional connectivity between hubs deemed ‘critical’ for successful entrainment (Johnson et al., under review; Bonilha et al., 2019) . As an adjuvant to behavioral approaches for rehabilitation, noninvasive brain stimulation (NIBS) techniques improve therapy outcomes (Baker et al., 2010; Fridriksson et al., 2011; Fridriksson et al., 2018; Meinzer et al., 2016; Marangolo et al., 2014). One NIBS method, transcranial alternating current stimulation (tACS), is unexplored as a method to boost aphasia therapy outcomes. tACS is hypothesized to entrain endogenous rhythms at the frequency of stimulation (Ali et al., 2013; Herrmann et al., 2013) and induce synaptic changes via spike timing dependent plasticity (Vossen et al., 2015; Zaehle et al., 2010) to modulate behavioral effects. The current study aims to determine if tACS will improve SE performance among individuals with chronic NFA. Methods In a proof-of-concept study, transcranial alternating current stimulation (tACS) will be paired with SE in a cohort of 20 patients with NFA in a within subjects, double-blind study. 1 mA of tACS at a frequency of 7 Hz (theta frequency) will be applied to perilesional LH anterior and posterior regions to modulate network coherence across three conditions: 1) in-phase; 2) out-of-phase; and 3) sham while participants mimic an audiovisual model (SE). The primary aims of the current investigation are as follows: 1) Does tACS boost behavioral outcomes (as measured by speech fluency: different words per minute) as compared to performance in the sham and out-of-phase conditions? 2) To what extent does stroke-induced damage (as measured by lesion characteristics [proportion of damage] and neural connectivity [structural/functional]) predict behavioral responses to tACS? Results Pilot data for this study will be collected throughout the summer of 2021 and preliminary behavioral and neuroimaging results will be presented at the SNL 2021 Conference. It is hypothesized that tACS will provide an exogenous boost of in-phase frontotemporal theta coupling to enhance frontotemporal network connectivity, facilitate neural integration, and subsequently, improve SE performance. We predict that a greater proportion of spared frontotemporal cortical regions will yield better modulatory effects of neural coherence for improved behavioral outcomes. Conclusion There is a critical need for effective and efficient rehabilitation paradigms to treat poststroke aphasia. Supplementing an evidence-based behavioral paradigm with a novel application of NIBS to modulate LH network coherence may yield a more efficient application of this behavioral therapy. Pilot data will contribute to the growing body of research investigating noninvasive brain stimulation as an adjuvant to traditional speech-language therapy.