Brain Connectivity and Aging

here is growing evidence that in the aging process both the neural and the vascular aspects of brain function are affected. On the neural side, aging is associated with damage to the myelin sheaths and reduction in the total number of nerve fibers, resulting in a reduction in structural connectivity [1]. But connections in the brain are not only structural (i.e. synapses, axons, etc.); equally important are blood flow related (vascular) connections. This hypothesis arose after the first observation that blood flow increased and decreased simultaneously in the two motor regions in opposite brain hemispheres. We call regions such as these functionally connected. As we get older, so does our brain’s vascular system: the elasticity of small blood vessels in the brain diminishes in some persons [2] and white matter lesions of presumed vascular origin increase [3]. These vascular changes affect blood flow to neurons and thus may reduce functional connectivity. The extent to which these vascular-related phenomena contribute to age-related reductions in structural or functional connectivity (and perhaps to cognitive decline) is not yet clear.