Several structural and molecular changes occur with age in the dog brain and are linked to cognitive function. In vivo brain imaging studies show that cortical atrophy [44] and ventricular widening [44], [45] and [46] are consistent features of canine brain aging. Further, MRI studies suggest differential vulnerabilities of specific brain areas to aging. For example, in aging dogs, the prefrontal cortex loses tissue volume at an earlier age (approximately 8–11 years) than does the hippocampus (after 11 years) [47]. The extent of cortical atrophy is significantly associated with cognition; animals with extensive atrophy perform more poorly on tests of learning and memory [48], similar to elderly humans with dementia [49] and [50]. Another similarity that has been reported between human brain aging and the canine is the spontaneous development of white matter hyperintensities seen with T2 imaging particularly in the white matter adjacent to the lateral ventricles [45]. Mechanistically this may be linked to changes in the capillaries of the white matter that have been reported to show a decrease in laminin immunoreactivity and iron deposits within astrocytes and macrophages, all of which suggest blood–brain barrier and white matter compromise [51].