Multi-decade hippocampal and amygdala volume analysis: equal variability and limited age effect.

Hippocampal (HC) and amygdala (AG) variability throughout asymptomatic adulthood have not been often characterized. The prevailing assumption is that HC/AG variability is small in young adults, and widens with advancing age and pathology. More recent studies with samples at every decade have reported conflicting results. Our goal was to perform a precise investigation of the effects of Age, Sex and Hemisphere on HC/AG volumes throughout aging. Subjects - we included 422 subjects from the Italian Brain Normative Archive database. Subjects ranged in age from 20 to 84 years. Data - manual segmentation was performed on 422 individuals for the HC, and 228 for the AG, using the Pruessner protocol. Statistical analysis - we tested the influence of total intracranial volume normalization, and used a hierarchical regression model to determine the shape of the association for Age with HC/AG volumes, for both Sex and Hemisphere variables. We explored the distribution of HC/AG volume across age groups by dividing the data into six different strata by decades, and compared volume variability using ANOVA. The study revealed that HC or AG volumes were not significantly related to Age or Age(2), regardless of Sex, except in the right AG. There were no significant differences in variability across age strata. This study lends credence to counter-intuitive notions regarding HC/AG neurodegeneration. Further, researchers can use our HC/AG volumes, broken down by sex and age, as normative data in future fundamental and clinical research.