Hippocampal atrophy is the critical brain change in patients with hypoxic amnesia

Anoxia is considered a good model for studying amnesia. However, not all individuals who experience anoxic events develop memory problems. Moreover, the question still remains about whether, after anoxia, damage is limited to the hippocampus in patients with amnesia and without other significant cognitive deficits. Here we investigated brain damage in a selected sample of adults affected exclusively by an amnesic syndrome after an anoxic episode. The cerebral MR images of these patients were submitted to visual inspection, volumetric measurements of the mesial temporal structures following manual segmentation, and to Voxel-Based Morphometry of the whole brain. We studied five anoxic patients and thirty-three well-matched healthy subjects. Our aim was to: (a) quantify regional atrophic changes associated with chronic anoxic damage compared to control subjects (Group Comparison Analysis); (b) identify regions of common abnormality across all patients (Conjunction Analysis in the VBM); (c) investigate whether measures of regional volume reduction correlated with neuropsychological memory scores; (d) compare the results obtained with visual inspection and ROI analyses with those obtained with VBM. We found that anoxic patients presented a significant reduction of gray matter volume in the hippocampus bilaterally compared to healthy subjects. The only common atrophic region across all patients was the hippocampus bilaterally. Correlation analysis showed only a trend between the Prose immediate free recall test and the left hippocampus. Our findings confirm that the hippocampus is very sensitive to damage stemming from anoxia. Patients with hypoxic amnesia may present damage in other brain regions, but only hippocampal atrophy is common in all of them.