MRS was performed on all subjects in 2 regions using constant time point-resolved spectroscopy (CT-PRESS) (Dreher and Leibfritz, 1999) with voxels manually positioned in left frontal white matter and left thalamus (Fig. 1). The following voxel dimensions (medial/lateral × superior/inferior × anterior/posterior) were used: frontal white matter, 20.0×20.0×18.4mm3 = 7.4cc; thalamus, 20.0×20.0×19.2mm3 = 7.7cc. The MRS acquisition sequence (~9min per voxel) used the following parameters: chemical shift (CS) encoding steps = 129, Δt1/2 = 0.8ms, TE= 139ms, TR = 2s, averages = 2 (Mayer and Spielman, 2005). A scan without water suppression was acquired (17 CS encoding steps, Δt1/2 = 6.4ms, 2 averages) to measure the tissue water content used to normalize the metabolite signal intensities. Data acquired without water suppression aided in metabolite quantification and were apodized in acquisition time (t2) with a 5Hz Gaussian line broadening and zero-filled to 4K points for each TE.
