EVIDENCE OF MULTIPLE MEMORY-SYSTEMS IN THE HUMAN BRAIN - A [F-18] FDGPET METABOLIC STUDY

Patients with global amnesia of different aetiologies (n = 11), and pa tients with probable Alzheimer's disease of recent onset and mild to m oderate severity (n = 18) underwent extensive neuropsychological exami nation, which included the evaluation of multiple components of memory , and a measurement of regional cerebral glucose metabolism with [F-18 ]fluoro-deoxyglucose ([F-18]FDG) and PET. In the neuropsychological te sts, both global amnesia and Alzheimer's disease patients had impaired episodic long-term memory, while deficits of short-term, semantic and implicit memory were present only in Alzheimer's disease. When local metabolic rates for glucose were compared with values from age- and ed ucation-matched normal controls, a common pattern of bilateral hypomet abolism was present in the hippocampus, cingulate and frontal basal co rtex of both global amnesia and Alzheimer's disease patients. On the o ther hand, significant hypometabolism was found in the thalamus in onl y global amnesia, and in the frontal, parietal and temporal associativ e cortex in only Alzheimer's disease. The results of a multivariate re gression analysis of test scores with metabolic data indicated that di fferent clusters of cerebral areas were associated with each of the ma in components of memory function. These data are in agreement with 'ne ural network' models of the neural basis of cognition, according to wh ich complex functions are subserved by multiple interconnected cortica l and subcortical structures.