Human sensory stimulation and deprivation: positron emission tomographic results and strategies

Fluorine-18-labeled fluorodeoxyglucose was used to measure local cerebral glucose metabolism by means of positron emission tomography (PET) in patients and in normal subjects. Various states of audiovisual stimulation and deprivation were explored. Our experience in performing neurobehavioral PET studies in over 145 normal right-handed individuals is described. In normal subjects metabolic left-right symmetry was found in states of partial sensory deprivation (eyes patched or ears plugged). Metabolic asymmetries (right less than left) were observed in subjects with more complete sensory deprivation (eyes patched and ears plugged). Auditory stimulation studies in normal subjects demonstrated metabolic evidence of cerebral lateralization. No correlation between site of metabolic response and side of stimulation was observed. Both the site and the side (left versus right) of maximal metabolic response correlated with the type (verbal versus nonverbal) and content of the stimulus as well as with the strategy used by the subject to solve the listening task. Visual stimuli of increasing complexity produced symmetrical increases in metabolic rate for the primary and secondary visual cortices. Focal stimulation of the central portion of the retina produced focal responses limited to the occipital poles, while full-field visual stimulation produced increased metabolic activity throughout the entire extent of the primary visual cortex. Patients with lesions of the visual pathway that spared the visual cortex itself demonstrated abnormalities in visual cortical metabolic rate that correlated with clinical symptoms. The refinement of neurobehavioral PET studies is discussed in terms of the limitations presently induced by spatial resolution, temporal resolution, anatomical localization accuracy, experimental neuropsychological paradigm design, and data analysis techniques. These limitations, as well as future prospects for using PET to study human brain function in both normal and pathological states, are discussed.