Aging: Body and Mind
The aging process generally results in a loss of memory and intellectual function. Age is a major risk factor for most common neurodegenerative diseases, including mild cognitive impairment, Alzheimer's disease , cerebrovascular disease, Parkinson's disease, and Lou Gehrig's disease. While much research has focused on diseases of aging, there are a few informative studies on the molecular biology of the aging brain. Many of these molecular changes are due in part to a reduction in the size of the brain, as well as loss of brain plasticity.
Brain plasticity is the brain's ability to change structure and function. The brain's main function is to decide what information is worth keeping and what is not. If there is an action or a thought a person is not using, the brain will eliminate space for it, rendering it incapable of functioning. Memory also degenerates, so older adults have a harder time remembering and attending to information. In general, an older person's procedural memory stays the same, while working memory declines. Procedural memory is memory for the performance of particular types of action; it guides the processes we perform and most frequently resides below the level of conscious awareness. In contrast, working memory is the system that actively holds multiple pieces of transitory information in the mind, where they can be manipulated. The reduced capacity of the working memory becomes evident when tasks are especially complex. Semantic memory refers to the memory of the meaning of things, events, understandings, and other concept-based knowledge. This type of memory underlies the conscious recollection of factual information and general knowledge about the world, and remains relatively stable throughout life.
Brain size and composition changes along with brain function. Computed Tomography (CT) studies have found that the cerebral ventricles expand as a function of age in a process known as ventriculomegaly. More recent MRI studies have reported age-related regional decreases in cerebral volume. The loss of neurons within the cerebral cortex occurs at different rates with some areas losing neurons more quickly than others. The frontal lobe and corpus callosum tend to lose neurons faster than other areas, such as the temporal and occipital lobes. The frontal lobe is responsible for the integration of information, judgement, and reflective thought. The cerebellum, which is responsible for balance and coordination, eventually loses about 25 percent of its neurons as well.
Other physical changes also occur in late adulthood. Women tend to live longer than men (by an average of 5 years) for a variety of reasons (for example, women tend to be more resilient to diseases). For both men and women, skin becomes drier and more wrinkled, and hearing and vision usually decline. The immune system starts to malfunction, increasing the risk of illness, cancer, diabetes, and other ailments. Many older adults suffer from insomnia - the inability to fall or stay asleep. Some even develop a condition called sleep apnea. Sleep apnea occurs when breathing ceases for at least 10 seconds, resulting in the person being awakened. Seniors also experience a decrease in mobility and a loss of balance which can result in falls and injuries.