Corpus Callosum Diffusivity Alteration is a Component of Healthy Aging in the Canine

The aging brain is known to alter in structure, connectivity and diffusivity in the human. Most notably the corpus callosum is observed to exhibit alterations in diffusivity values and, associated with this, right-left cerebral connectivity is reduced.  The aging canine brain has been observed to reduce in volume however the effect of aging on corpus callosum diffusivity has not been evaluated. In this study we applied the novel technique of voxel-based-analysis to identify the extent and location of significant diffusivity abnormalities in the brain of healthy aged canines. Diffusion tensor imaging data were acquired from 20 neurologically and behaviorally normal mesaticephalic canines grouped into young (aged between 2-6 years) and old (aged between 10-11 years) cohorts.  The data were skull stripped, corrected for noise, phase distortion, motion and eddy-current distortion. Tensor metrics FA and MD were calculated and voxel-based statistics applied a two-sample t-test to identify significant differences between age groups. Family-wise error corrected was used to correct for multiple comparisons. There were significant decreases in FA within the body and dorsal fibers for the corpus callosum in FA in the aged canine group when compared to the younger group. Similarly, there were significant decreases in MD in the corpus callosum in the aged group though these decreases were less widespread. Healthy aging is associated with decreases in FA and MD within the corpus callosum. This is similar to the diffusivity changes present within humans and may reflect alterations in structural connectivity between hemispheres.