Detailed Experimental: Baseline measures of mood will be assessed with the Activation subscale of the Internal State Scale (ISS) (primary measure), Hamilton Depression Rating Scale (17-item version), and Young Mania Rating Scale (YMRS). Cognition will be assessed with the HVLT-R (primary measure), and STROOP color word task. The subjects will be given memantine or identical appearing placebo as described above. Reductions in dosage will be allowed should clinically significant side effects emerge based on the judgment of a blinded psychiatrist. The above cognitive measures will be administered at each assessment visit (8 total); during the assessments at week 2 and week 14 patients will also be given 3 mood questionnaires. Each visit will be approximately an hour and half in length. The RA doing assessments will be blinded at all times. Alternative but equivalent versions of the HVLT-R will be given to minimize practice or learning effects. Current and cumulative corticosteroid dose (mg each day X number of days) will be determined and recorded.