Study procedures
EVENTS
This study was preregistered at ClinicalTrials.gov with identifier NCT04647032 (first registered 11/30/2020, see Supplementary Information for procotol). In this study, participants first met with researchers at the University of California, San Francisco and provided informed consent. Participants received two iPad tablets, one for tACS days and one for outcome measures days. Participants were instructed on the use of each device (with a brief demonstration in front of a mirror with the tACS patches), the timeline of events, and provided with detailed written instructions. Once home and with active internet, participants first completed the outcome measure tasks without any neurostimulation (baseline). On the following day, participants self-applied the neurostimulation device and then completed 20-min of adaptive CCT. Participants completed the paired tACS + CCT task in the same manner for the following four days, totaling five consecutive days. On the following (sixth) day, participants completed the same outcome measures as baseline without any concurrent tACS (1-week assessment). The next day, one week from the initial session, participants completed the adaptive CCT task with paired tACS again. Participants then had two additional weekly sessions of tACS + CCT. Finally, on the day after the last (eighth) tACS session, participants completed a final tACS-free outcome measures session (1-month assessment; Fig. (