Investigating neurobiological and cognitive changes following transcranial direct current stimulation in healthy aging and mild cognitive impairment EMONSONMELANIE ROCHELLE LUEHMAN 2019 Aging is associated with cognitive decline. Transcranial direct current stimulation (tDCS) may serve as a potential method to improve cognition. This thesis examined the neurobiological and cognitive effects induced by tDCS in younger adults, older adults, and mild cognitive impairment (MCI). MCI may represent a prodromal stage of dementia. Findings indicated that response to tDCS differs based on age and/or presence of cognitive impairment. Further, adaptability of the brain, and impact on cognitive performance, varies in healthy and pathological aging. These factors should be considered when developing and applying therapeutic brain stimulation techniques for use in the aging brain.