Can transcranial direct current stimulation counteract age-associated functional impairment?

Transcranial direct current stimulation (tDCS) can improve motor and cognitive function in young individuals and may be a viable tool to counteract age-associated functional impairment. We review the growing body of research that investigated tDCS-effects in aging and attempt to provide a framework to guide future research in this emerging field. The majority of thirty reviewed studies (N=856 older participants) reported beneficial behavioral tDCS-effects across functional domains. Eleven studies included young and older adults and demonstrated that tDCS can restore impaired motor and cognitive functions. Several studies highlighted differences in the extent and timing of tDCS-effects between age-groups and the importance of mediating factors like baseline performance levels. Multi-session tDCS improved cognitive training outcome in two studies, however, limited transfer to untrained materials was reported. Montages inducing beneficial effects in young adults did not improve or even impaired performance in older adults in several studies. Thus, a cautious and more systematic approach that incorporates information about age-associated brain reorganization is advised when aiming to induce more permanent neuroplastic effects in older individuals in future studies.