INS and obesity due to melanocortin 4 receptor deficiency: We found only total occipital NAA concentrations to be lower in subjects with obesity, which reproduces the findings from parietal, prefrontal and fontal cortex as well as hippocampus from previous studies in insulin resistant or obese subjects.37, , –40 As NAA is synthesized almost exclusively in neurons in the brain,41 and decreased concentrations have been associated with aging and several neurodegenerative diseases,42, , , –46 lower NAA concentrations have been attributed to neuronal damage in obesity.