Effects of Electrical Stimulation on Verbal Learning in Typical and Atypical Alzheimer's Disease

The investigation implements a double-blind, sham-controlled, within-subject, cross-over design that allows for the evaluation of the cognitive and neural effects of word-list learning as modulated by tDCS compared to sham stimulation. Participants in all groups will receive word-list learning intervention (WordLLI)+ High-Definition tDCS (HD-tDCS) or WordLLI+ sham in Period 1 or 2, randomized for the Period 1 stimulation condition. Each learning Period will last 2 weeks, with 5 learning sessions per week (for a total of 10 learning sessions per Period) with a 3-month (stimulation-free) wash-out period between the two Periods. The intensity, total number of learning sessions and number of learning items is consistent with most other tDCS studies in neurodegenerative disorders and the investigators have used this design successfully over the past 7 years in neurodegenerative disorders (PPA, mild AD). Stimulation is implemented every weekday to take advantage of the long-term potentiation induced by tDCS as found in early multi-session studies. A tDCS-only condition (without any intervention) is not implemented in this design because no study to date has shown improvement on motor, cognitive, or language performance after anodal tDCS-only for 2 or even more weeks. After each period the investigators will perform 1-month and 3-month follow-up sessions for evaluation purposes. For those participants who are long-distance, at the 1-month time point only the investigators may use a video conferencing tool such as GoToMeeting to administer the assessments. This is to mitigate the costs of travel for a short appointment.