Discussion
ADVERSE EVENTS
This study demonstrated the feasibility of conducting remote tACS + CCT in an at-home setting with clinical populations without direct researcher supervision. The md-aMCI participants reported zero serious adverse events, overall subtle side effects, and only a 10% attrition rate (3 of 30). While we observed that each tACS group improved on the multitasking CCT task, only the theta tACS group exhibited a significant transfer of benefit to improved sustained attention ability, inhibitory control, and attentional orienting, suggesting multiple aspects of attentional control may have been facilitated by the intervention. These gains were limited to attentional tasks as visual search performance and WM capacity were not affected. Together, these results show that tACS + CCT at home is a safe and feasible means to target cognitive control in md-aMCI populations, but the beneficial effects of tACS appear limited to cognitive functions which share neural mechanisms with the CCT paradigm.The observed 10% attrition rate is the same rate as our previous tACS studiesWe showed that multitasking performance was similarly improved in both the theta and delta (control) tACS groups after 5 tACS sessions, without additional gains after 8 sessions. We speculate that theta tACS may help facilitate learning the CCT task at a faster rate (i.e., within a few days), but that in time, performance in the control group will catch up to the theta tACS group due to practice effects. This interpretation is in line with our previous research demonstrating that theta tACS facilitates multitasking performance in young adults after 1 dayHere we observed that theta tACS + CCT exhibited a transfer of benefit to domains that share similar task demands with the divided attention CCT: sustained attention, inhibitory control, and attentional orienting (Fig. In the current study we note that the three additional weekly “booster” sessions did not yield any additional benefit, although gains were maintained throughout the length of the study. Therefore, this provides guidance regarding tACS dosing, such that five (or possibly fewer) sessions is needed to improve sustained attention in an md-aMCI population. Additional research will be required to assess how long such effects may last, the proper number of sessions per individual, and if training gains also slowed future decline in related cognitive domains. Our previous research in healthy older adults showed tACS-related improvements in multitasking ability lasted at least one monthOnce tACS benefits become apparent, it is unclear whether additional tACS sessions are necessary because we did not observe additional gains at the 1-month time point, following three weekly “booster” tACS sessions. Further research will be required to understand whether these weekly booster sessions had no effect, or whether they served to maintain the benefits achieved after the first week. Given that individuals who need cognitive remediation the most (e.g., clinical populations) are also the ones who benefit most from neuromodulationOur previous research with theta tACS coupled with multitasking CCT found that individual differences in older adult neuroanatomy and neurophysiology both predicted tACS efficacyFinally, remote neurostimulation research has primarily been conducted in clinical populations, where researchers were often present via teleconferencing (reviewed in: