FDG-PET analysis and findings in amnesia resulting from hypoxia

The assumptions underlying neuroimaging, and problems in its analysis and i nterpretation, are commonly underestimated in neuropsychology. The ways in which fluoro-deoxy-glucose (FDG) positron emission tomography (PET) data ca n be analysed are discussed. PET findings from four patients who had suffer ed severe amnesia, following episodes of acute hypoxia, are presented. Thes e patients had shown evidence of medial temporal (hippocampal and parahippo campal) atrophy on MRI brain scans. The PET data were analysed in several d ifferent ways. The converging findings were that the patients showed bilate ral thalamic hypometabolism, and there was also evidence of retrosplenial h ypometabolism bilaterally, Cognitively, these patients performed most like other patients with medial temporal lesions, but the results indicate that structural lesions can have distal metabolic effects on structures elsewher e. These findings are interpreted in the light of neuroanatomical observati ons concerning parallel projections between medial temporal lobe structures and the thalamus, some of which pass via the retrosplenium.