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Background-If they are to be replicable, MRI volume measurements require explicit definitions of structures and of criteria for delineating these structures on MRI. Previously published volumes in healthy subjects show considerable diVerences in measurements across diVerent studies, including a fourfold variation in estimates of hippocampal volume. Previous neuroimaging reports in patients with KorsakoV syndrome have generally found widespread or non-specific change, whereas in patients with herpes encephalitis the extent of pathological involvement reported beyond the temporal lobes has varied. Method-In the present study, a clear set of anatomical criteria and detailed MRI segmentation procedures were applied to measure whole brain, frontal and temporal lobe, and anterolateral and medial temporal volumes, as well as thalamic areas in patients with organic amnesia (from KorsakoV's syndrome, herpes encephalitis, and focal frontal lesions) as well as healthy controls. Results-Patients with KorsakoV's syndrome showed decreased thalamic measurements but no significant changes in the medial temporal lobes, whereas patients with herpes encephalitis showed severe medial temporal but not thalamic atrophy. In the patients with known frontal lobe lesions, quantitative analysis on MRI showed reduced frontal lobe volume but no significant temporal lobe or thalamic atrophy. Conclusion-Quantified MRI can be a useful technique with which to examine brain-cognitive relations, provided that detailed techniques are explicitly described. In particular, specific patterns of volume change can be found in vivo in patients with KorsakoV's syndrome and those with herpes encephalitis. (J Neurol Neurosurg Psychiatry 2001;71:13-22)

The assumptions underlying neuroimaging, and problems in its analysis and interpretation, are commonly underestimated in neuropsychology. The ways in which fluoro-deoxy-glucose (FDG) positron emission tomography (PET) data can be analysed are discussed. PET findings from four patients who had suffered severe amnesia, following episodes of acute hypoxia, are presented. These patients had shown evidence of medial temporal (hippocampal and parahippocampal) atrophy on MRI brain scans. The PET data were analysed in several different ways. The converging findings were that the patients showed bilateral thalamic hypometabolism, and there was also evidence of retrosplenial hypometabolism 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 elsewhere. These findings are interpreted in the light of neuroanatomical observations concerning parallel projections between medial temporal lobe structures and the thalamus, some of which pass via the retrosplenium.

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