Enhancing Neuroplasticity and Frontal Lobe Function in Patients With Mild Alzheimer's Disease

In this study, the investigators aim at assessing and then enhancing neuroplasticity in the dorsolateral prefrontal cortex (DLPFC) and working memory - a key function of DLPFC - in patients with mild AD. The investigators will use a novel non-invasive brain stimulation approach, Paired Associative Stimulation (PAS). PAS simulates in humans the induction of long-term potentiation (LTP), a prototype of synaptic neuroplasticity. PAS involves the repetitive pairing of electrical stimulation of the median nerve with - 25 ms later - transcranial magnetic stimulation (TMS) of the contralateral DLPFC. As such, these two stimulations arrive simultaneously in the DLPFC and result in potentiation of TMS induced cortical evoked potential, analogous to in vitro LTP. Specific Aim 1: To compare LTP in the DLPFC among patients with mild AD and healthy subjects. Specific Aim 2: To assess the effect of a 2-week course of PAS (rPAS) as applied to the left DLPFC on LTP and performance on working memory in patients with mild AD in comparison with a 2-week course of PAS control condition (PAS-C, described below) (rPAS-C).