Local cerebral glucose metabolic response to audiovisual stimulation and deprivation: studies in human subjects with positron CT.

Positron computed tomography (CT) and 18-F fluorodeoxyglucose (FDG) were used to measure local cerebral glucose metabolism (LCMRGlc) in patients and normal subjects during auditory and visual stimulation and deprivation. Sixty-six studies were performed in 42 individuals. In normal subjects metabolic left-right symmetry was found in states of partial (eyes patched or ears plugged) sensory deprivation. Visual stimuli of increasing complexity produced symmetric increases in LCMRGlc of the primary and associative visual cortices. Patients with lesions of the visual pathway but sparing the visual cortex demonstrated abnormalities in visual cortical LCMRGlc that correlated with clinical symptoms. Auditory stimulation studies in normal subjects demonstrated metabolic evidence of hemispheric specialization. The side (left versus right) and site of maximal metabolic response correlated with the type (verbal versus nonverbal) and content (factual story, chords, tone sequences) of the stimulus as well as the strategy used by the subject to solve the listening task. There was no correlation between the site of metabolic response and side of stimulus presentation. The results of these studies demonstrate that positron CT provides new and previously unattainable information about local human brain physiology in normal and pathological states. The limitations, advantages and future prospects of using these methods to study human brain function are discussed.