Memantine is an NMDAR antagonist that has been reported to be effective therapeutically in Alzheimer disease. It has been available in Germany as well as in most of the European Union for more than two decades. Recently, it has been approved for moderate to severe dementia in the US. The chemical name for memantine hydrochloride is 1-amino-3,5-dimethyladamantane hydrochloride. Memantine is an uncompetitive, moderate affinity, antagonist of NMDARs. It has been proposed that therapeutic doses of this drug inhibit the pathological effect of NMDAR activation while leaving unaffected NMDAR-mediated physiological processes involved in learning and memory. Recent preclinical data from the laboratory of this trial's P.I. on the mouse model for DS (Ts65Dn) have suggested a dysregulation of NMDAR activity in these animals and demonstrated improvement on learning and memory measures by the use of acute doses of memantine.