The brain is very complex, and is composed of many different areas and types of tissue, or matter. The different functions of different tissues in the brain may be more or less susceptible to age-induced changes. The brain matter can be broadly classified as either grey matter, or white matter. Grey matter consists of cell bodies in the cortex and subcortical nuclei, whereas white matter consists of tightly packed myelinated axons connecting the neurons of the cerebral cortex to each other and with the periphery. Loss of neural circuits and brain plasticity
Brain plasticity refers to the brains ability to change structure and function. This ties into the common phrase, "if you dont use it, you lose it," which is another way of saying, if you dont use it, your brain will devote less somatotopic space for it. One proposed mechanism for the observed age-related plasticity deficits in animals is the result of age-induced alterations in calcium regulation. The changes in our abilities to handle calcium will ultimately influence neuronal firing and the ability to propagate action potentials, which in turn would affect the ability of the brain to alter its structure or function (i.e. its plastic nature). Due to the complexity of the brain, with all of its structures and functions, it is logical to assume that some areas would be more vulnerable to aging than others. Two circuits worth mentioning here are the hippocampal and neocortical circuits.
Aging is a major risk factor for most common neurodegenerative diseases, including mild cognitive impairment, dementias including Alzheimers disease, cerebrovascular disease, Parkinsons disease, and Lou Gehrigs disease. While much research has focused on diseases of aging, there are few informative studies on the molecular biology of the aging brain (usually spelled ageing brain in British English) in the absence of neurodegenerative disease or the neuropsychological profile of healthy older adults. However, research suggests that the aging process is associated with several structural, chemical, and functional changes in the brain as well as a host of neurocognitive changes. Recent reports in model organisms suggest that as organisms age, there are distinct changes in the expression of genes at the single neuron level. This page is devoted to reviewing the changes associated with healthy aging. Structural changes
Aging entails many physical, biological, chemical, and psychological changes and the brain is no exception to this phenomenon. These various changes have attempted to be mapped by conceptual models like the Scaffolding Theory of Aging and Cognition (STAC) in 2009. The STAC model looks at factors like neural changes to the white matter, dopamine depletion, shrinkage, and cortical thinning .CT scans have found that the cerebral ventricles expand as a function of age. More recent MRI studies have reported age-related regional decreases in cerebral volume. Regional volume reduction is not uniform; some brain regions shrink at a rate of up to 1% per year, whereas others remain relatively stable until the end of the life-span.