Aging of corticospinal tract fibers according to the cerebral origin in the human brain: A diffusion tensor imaging study

The corticospinal tract (CST) is known to originate from multiple cerebral areas, including the primary motor cortex (M1). In this study, using diffusion tensor imaging (DTI), we attempted to investigate the differences of aging of CST fibers according to the cerebral origin in the human brain. Sixty healthy subjects aged from the 20s to the 70s were recruited, and 10 subjects were assigned to each age group. CST fibers were reconstructed from the M1 (Broadmann's area [BA] 4), the secondary motor area (M2, BA 6), and the primary somatosensory cortex (S1, BA 1-3), respectively. Values of fractional anisotropy (FA), mean diffusivity (MD), and tract volume (TV) of CST fibers from each cerebral area were measured. Significant differences in the TV values of CST fibers from the M2 were observed between the 70s age group and the other age groups, except the 60s age group (p < 0.05). However, no significant difference in the values of FA and MD of CST fibers from the M2 were observed between age group (p > 0.05). No significant differences in the values of FA, MD, and TV of CST fibers from the S1 and M1 were observed between age groups (p > 0.05). We found that the fiber number of CST fibers from the M2 was decreased in the 70s age group compared with the 20s-50s age groups. Because the main function of the M2 is motor planning and coordination, our results would be helpful in development of strategies for coping with aging of the CST.