Transcranial alternating current stimulation applied to language recovery in persons with aphasia: a scoping review

Background: Aphasia leads to alterations in functional brain connectivity and abnormal patterns of neural oscillations. Transcranial alternating current stimulation (tACS) is a non-invasive technique that entrains brain oscillations at a given frequency. A growing body of evidence suggests that tACS can be effective in neurological disorders. Aims: This review was originally aimed at assessing the impact of tACS on language recovery in persons with aphasia (PWA). Because of the paucity of studies focusing on this issue, the survey was extended to also include its application to healthy individuals (HI). Methods & Procedures: A first search of studies focusing on the application of tACS on PWA was conducted. A second search concerned the effect of tACS on language processing in HI. Results: Of the 236 screened studies (23 for the first search, 213 for the second one) seven were eligible for the review. Three studies applied tACS to improve the treatment of aphasia and four administered tACS to study language function in HI. Conclusions: Although only few studies have investigated the application of tACS as an adjunct to speech and language therapy in PWA, the preliminary results are promising. Moreover, to date, little evidence is available on the investigation of how language processing is affected by tACS. Despite this, commonalities and critical issues in current knowledge are discussed, along with suggestions for future studies.