The primary objectives of this prospective, non-controlled, pilot study are to assess the feasibility and safety of DBS in AD patients with mild cognitive and memory impairment, and to evaluate the efficacy of DBS to slow down or stabilize this decline. Five patients with AD (DSM IV) diagnosed less than two years, with mild cognitive decline (MMSE 20-24), and specific impairment of episodic memory will be included in a 2-year period. The evaluation criteria for feasibility will be the proportion of patients undergoing the procedure, chronic stimulation and evaluation process without adverse event (AE). Efficacy will be evaluated using numerous cognitive and memory testing including classical instrument used in AD clinical trials. Changes in behavioral scales, and changes in hypothalamic functions (clinical, biological and hormonal assessment) will evaluate safety and tolerance. Clinical, neuro-psychological, biological and imaging assessment will be performed 3 and one month before and 3, 6, 12 and 24 months after surgery. Bilateral electrodes (Medtronic 3389) will be implanted, by MR-guided frame-based stereotaxy, in the hypothalamic part of the fornix, and then connected to the generator (Kinetra, Medtronic). Chronic high-frequency stimulation will be delivered immediately after surgery.