Fields or flows? A comparative metaanalysis of transcranial magnetic and direct current stimulation to treat post-stroke aphasia

Purpose: Aphasia-acquired loss of the ability to understand or express language-is a common and debilitating neurological consequence of stroke. Evidence suggests that transcranial magnetic (TMS) or direct current stimulation (tDCS) can significantly improve language outcomes in patients with aphasia (PWA). However, the relative efficacy between TMS and tDCS has not yet been explored. Mechanistic and methodological differences, patient inclusion/exclusion criteria and experimental designs may influence observed treatment benefits. Methods: We conducted a systematic review and meta-analyses of TMS and tDCS treatment studies in PWA. Standard mean difference (SMD) for changes in picture naming accuracywas estimated; pooled SMDs were compared using a random-effects model. Results: Eight TMS (N= 143) and 8 tDCS studies (N= 140) met our inclusion criteria. Pooled SMDs of 0.448 (p < 0.001) in favor of TMS, and 0.395 (p < 0.001) in favor of tDCS were found. Between-subject designs were more common in subacute and within/crossover designs in chronic patients. TMS SMDs were significant in both chronic (SMD = 0.348) and subacute (SMD = 0.667) populations while those for tDCS were significant in chronic (SMD = 0.320) but not in subacute (SMD = 0.283) PWA. Conclusions: The magnitude of treatment effects appears to be consistent between TMS and tDCS in PWA. Larger-scale clinical trials should further substantiate our findings.