The most consistent and pronounced factor that affects the cognitive abilities of older adults is a decline in processing speed, or the rate at which people can perform a task.  Links between processing speed and changes in frontal lobe cortex, which appear to be mediated in part by cerebral vessel disease, have been reported previously.  Similar results are presented in our recent Frontiers of Human Neuroscience paper, as well as evidence that age-related changes in cerebellar cortex uniquely predict age-related changes in processing speed.  Cerebellar cortex did not appear to be substantially affected by vessel disease, suggesting different mechanisms for cerebellar and frontal changes that affect processing speed.  These results are important because potential lifestyle and intervention programs designed to limit the effects of aging on cognition could have greater efficacy by targeting distinct cerebellar and frontal systems.