CONSTRAINTS ON THE CEREBRAL BASIS FOR SEMANTIC PROCESSING FROM NEUROIMAGING STUDIES OF ALZHEIMERS-DISEASE

Objective-Functional activation studies of semantic processing in heal thy adults have yielded conflicting results. The purpose was to evalua te the relative role of the brain regions implicated in semantic proce ssing with converging evidence from imaging studies of patients with i mpaired semantic processing. Methods-Semantic memory was assessed in p atients with Alzheimer's disease using two measures, and these perform ance patterns were related to profiles of reduced cerebral functioning obtained with high resolution single photon emission computed tomogra phy (SPECT). Patients with frontotemporal degeneration were similarly evaluated as a control group. Results-Reduced relative cerebral perfus ion was seen in parietal and posterior temporal brain regions of patie nts with Alzheimer's disease but not patients with frontotemporal dege neration. Impairments on semantically guided category membership decis ion tasks were also seen in patients with Alzheimer's disease but not those with frontotemporal degeneration. Performance on the semantic me asures correlated with relative cerebral perfusion in inferior parieta l and superior temporal regions of the left hemisphere only in Alzheim er's disease. Relative perfusion was significantly lower in these regi ons in patients with Alzheimer's disease with semantic difficulty comp ared with patients with Alzheimer's disease with relatively preserved semantic processing. Conclusion-These findings provide converging evid ence to support the contribution of superior temporal and inferior par ietal regions of the left hemisphere to semantic processing.