Age-related metabolic reductions in 3 cognitively normal subjects. A: 80 year-old subject, demonstrating prefrontal and superior parietal hypometabolism with sparing of primary sensory-motor cortices. B: 76 year-old subject, showing mild hypometabolism in anterior cingulate cortex, medial frontal regions and insula. C: 82 year-old subject, demonstrating hypometabolism involving anterior cingulate cortex, medial frontal regions and insula.