The regional cereabral metabolic rate for glucose (rCMRglc) was examined as a measure of cerebral functional activity in 49 healthy men between the ages of 21 and 83 years. rCMRglc was determined by means of positron emission tomogrpahy (PET) with 18-F-2-fluorodeoxy-D-glucose, under resting conditions, when the subject's eyes were covered and his ears plugged to reduce sensory input. Average hemispheric glucose utilization in individual regions of the right and left hemispheres did not decline significantly with age (p greater than 0.05), even after correction for cerebral atrophy. The constancy of cerebral glucose utilization with aging demonstrates the principle of homeostasis, and probably reflects redundancy and plasticity of the healthy senescent brain. rCMRglc was examined in patients with Alzheimer's disease. Absolute metabolic rates did not differ between mildly and moderately demented patients and controls, but ratios of metabolic rates to rCMRglc in the sensorimotor and occipital cerebral cortices showed reductions. Asymetry of cerebral metabolism in mildly and moderately demented patients was shown to be unchanged and correlated with appropriate neuropsychological deficits over periods of up to 2 years. Patterns of cerebral metabolism were demonstrated, using Q-component analysis in patients with Alzheimer's disease, and shown to characterize different patient groups unrelated to severity of dementia. Cerebrial metabolism was assessed repeatedly in a 57 year old man.
