 The investigators proposed intervention is a combination of cognitive remediation CR and non-invasive brain stimulation - transcranial Direct Current Stimulation tDCS. Participants with MCI or MDD with or without MCI will be randomized to tDCS CR or sham palcebo tDCS sham placebo CR. Both CR and tDCS have been shown to induce neuroplasticity and improve cognition. The investigators hypothesize that their combination will enhance cognitive reserve and protect against cognitive decline and the onset of MCI in those with normal cognition or AD in those with MCI. 