MRS investigations of cognitive function in both normal and clinical samples suggest that individual variation in cognitive function can be predicted by NAA concentrations and NAA/Cre ratios, but important caveats need to be considered. Much regional variation exists in both neurometabolite concentrations. And, of course, brain regions and tissue compartments differ markedly in their function. Most of the work described in this chapter reflects analyses of white matter NAA. Future investigations will clearly need assess multiple white and gray matter regions across the brain and evaluate relationships with diverse measures of cognitive, motor, and emotional functions. The variables of sex and age may be found to moderate NAA-cognition relationships.
As it true of every neuroimaging modality, the meaning of individual observations using MRS will become clearer when this technique in used in conjunction with other neuroimaging approaches. Let us offer two examples. We have suggested that NAA variation might be especially important for speed of cognitive processing. Magnetoencephalography (MEG) has excellent temporal resolution  and processing latencies in specific anatomic regions can potentially be linked with neurometabolite variation in those same locations. Diffusion Tensor Imaging (DTI) might prove especially valuable in evaluating white matter structural variation  covarying with NAA concentrations.
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