Correlations between regional brain volumes and memory performance in anoxia

Abstract

This study was aimed at investigating the quantitative relationship between regional brain volumes (hippocampus, amygdala, as well as cerebrum, frontal lobe, parietal lobe, temporal lobe) and performance on anterograde and retrograde memory tests in anoxic patients. We used high-resolution MRI to measure brain volumes in 13 anoxic patients. Neuropsychological testing was conducted contemporaneously with MRI. To control for age and sex, neuroanatomical volume residuals were calculated using regression equations derived from a group of 87 healthy comparison participants. We found that anoxic patients with severe amnesia had hippocampal volumes that were 36% smaller than normal, whereas patients with mild or no amnesia had normal hippocampal volumes. Regional gray matter volumes in severe amnesic anoxics were substantially smaller than expected. Performances on anterograde memory tests were significantly correlated with hippocampal and regional gray matter volume residuals. There was a significant correlation between white matter volume (but not hippocampal volume) and performance on the Visual Retention Test, a multi-dimensional test of cognitive function. There were no significant correlations between neuroanatomical measures and performance on a retrograde memory test. Our results indicate a strong quantitative relationship between performance on anterograde memory tests and hippocampal and regional gray matter volume residuals. Correlations between white matter volume residuals and performance on the VRT were found to be independent of hippocampal volume. Given the strong correlation between hippocampal volume and total gray matter volume residuals, a quantitative, normalized measure of total gray matter volume may provide a good indication of clinical outcome in anoxia.