Tomographic mapping of human cerebral metabolism: sensory deprivation.

Local cerebral glucose metabolism was measured in 22 right-handed, normal volunteers using 18F-fluorodeoxy-glucose and positron computed tomography. Three states consisting of selective or combined auditory or visual deprivation were examined. Results demonstrated a progressive decline in overall glucose metabolism with reduced sensory inputs. The relative metabolism of the frontal cortex compared to that of the parietal and occipital cortex progressively increased from the eyes-closed to the both-closed states. Left-right symmetry was found throughout the distribution of structures within the region of brain samples for both the selective auditory and visual deprivation test conditions, but a relative decrease in right-sided metabolism occurred in the combined audiovisual deprivation state. The most significant metabolic asymmetries occurred in the perisylvian, inferior prefrontal, and lateral occipital cortex. The relative metabolic rates of the medial occipital cortex, measured as a percentage of the hemispheric mean, doubled bilaterally with eye opening. The results demonstrate the difficulties inherent in defining a stable and reproducible "resting" state for the human brain.