 Recent data show that marked cell damage precedes the clinical manifestation of Alzheimers disease AD. Hence, targeting populations at risk with pharmacological interventions is a possible strategy to lessen the burden of the disease. Cognitively normal individuals with subjective memory complaints SMC manifest biological characteristics consistent with early AD and are at risk for future cognitive decline. Family history of AD also constitutes a risk. In a previous study the investigators showed that memantine slows down the accumulation of phosphorylated tau in normal SMC subjects. Using a multivoxel high field MR spectroscopy MRS technique, the investigators also demonstrated that memantine decreased hippocampal glutamate. Both these findings may be consistent with the drugs anti-excitotoxic activity. In this new project the investigators propose to treat a sample of 12 presymptomatic individuals at risk SMC and family history of AD with memantine. This will be a double blind, placebo controlled study with a control group 12 non-treated subjects. The investigators will determine whether the effects of memantine as assessed by cognitive performance and MRS are present after 4 months of treatment and persist 2 months after discontinuation. MRS will be used to evaluate the effect of memantine on levels of the neurotransmitter glutamate and neuronal viability marker N-acetylaspartate NAA in the hippocampus. The investigators will test the following hypotheses: 