Age-related degeneration of corpus callosum in the 90+ years measured with stereology

The present study is aimed to assess age-related structural changes in corpus callosum with stereology in 21 postmortem human brains without neuropathology, of age 65-75 (Group A, n = 7), 80-85 (Group B, n = 7), and 94-105 (Group C, n = 7) years. Cross-sectional area, fiber number and density decrease in Group B compared with Group A, then remain unchanged in Group C. Mean fiber diameter increases with age. Cross-sectional area shows strong positive correlation to fiber numbers and negative correlation to mean fiber thickness. With age, modest but significant change in fiber size including a decrease in the percentage of 1-2-μm fibers and an increase in 2-3-μm fibers was observed. Fiber density shows a steeper decline with age in the anterior compared with posterior segments. Neurodegeneration is an ongoing process where the anterior corpus callosum is more susceptible to age-related degeneration. Corpus callosum cross-sectional area atrophy is mostly related to decline in fiber number and density rather than demyelination, with preferential disruption of small caliber fibers.