Patients treated with memantine exhibited a significant increase in the glutamate ( P = 0.010 ) , glutamate/creatine ratio ( P = 0.013 ) , combined glutamate + glutamine ( P = 0.016 ) and total N-acetyl-aspartate ( NAA+NAAG ) ( P = 0.034 ) in the posterior cingulate cortex compared with those on placebo .