Positron emission tomographic studies of perceptual tasks

Metabolic mapping in conjunction with positron emission tomography was used to examine the response of the human brain to physiological stimuli. Local cerebral glucose consumption was measured by means of the fluorine-18-labeled fluorodeoxyglucose technique. The coefficient of variation of this measurement for various gray matter structures varies from 19.5 to 26.4%. If repeat measurements are made in the same subject using carbon-11-labeled deoxyglucose as the tracer, the coefficient of variation of repeat measurements for these same structures is reduced to between 5.2 and 8.7%. Stimulation of one visual field in normal subjects produced a significant (p less than 0.01) increase in metabolism in the contralateral visual cortex. An auditory stimulus consisting of a tape-recorded factual story presented through earphones to only one ear produced a significant (p less than 0.001) increase in glucose consumption in the contralateral temporal cortex. The effects of vigilance or attention on cerebral metabolism were also examined. There was significantly greater metabolism in the right versus the left inferior parietal region in subjects attending to a visual or auditory task compared with those who were not. Anxiety appeared to produce significantly greater glucose utilization in the right hemisphere compared with the left in those subjects who had a higher level of anxiety during the measurement. Metabolic mapping promises to be a powerful new tool in furthering our understanding of the organization and functioning of the human brain.