Identification of seizure-mediating brain structures with the deoxyglucose method: studies of human epilepsy with positron emission tomography, and animal seizure models with contact autoradiography.

This chapter describes tomographic and autoradiographic studies of human and animal seizure syndromes employing Sokoloff's deoxyglucose method. The method's rationale rests on two principal facts: that adult brains normally utilize glucose almost exclusively as their exogenous energy source, and that deoxyglucose, a glucose analog, accumulates in brain cells in proportion to their activity level. Thus, computed tomography or contact autoradiography allows visualization and indirect measurement of changes in the activity of different brain structures under specified conditions, such as between, during, or immediately following seizures. In humans, partial seizures have been the most extensively studied, with 18F-fluorodeoxyglucose and positron emission tomography. Interictally, the brains of patients with partial seizures are characterized by hypometabolism that is particularly severe in the vicinity of seizure foci. In many cases, these focal hypometabolic zones become hypermetabolic ictally. Other brain areas may also become hypermetabolic ictally, or they may instead become hypometabolic. Often the physical extent of interictal hypometabolic zones is substantially greater than the extent of overt pathology. This indicates that hypometabolism can result from subtle, presently undescribed, structural or functional derangements, as well as from frank neuronal loss. A variety of animal seizure "models" have also been studied, with 14C-2-deoxyglucose and contact autoradiography. Each model has produced a unique deoxyglucose and contact autoradiography. Each model has produced a unique deoxyglucose utilization pattern, but thus far none that closely resembles any of the human seizure patterns. This probably reflects true differences between the mechanisms mediating different types of animal seizures and those mediating human seizures. Although in widespread use for only a few years, the Sokoloff method has already demonstrated its ability to distinguish among a variety of seizure types in both humans and animals, and to correctly identify those structures most involved in focal seizures. Thus, the method can be of great aid in narrowing the search for seizure-mediating mechanisms.