Dementia

Dementia is the loss of intelligence. All four features of sentience, sensing, acting, deciding, remembering, can be impaired by brain diseases that cause dementia. Dementia involves the loss of understanding, the disappearance of meaningful connections and confusion when only meaningless connections remain.  The 78 year old motorist stops at the green light and proceeds on the red light, crashing into another motorist who is following the rules correctly; a dementia diagnosis follows the accident. Since more humans are living to an old age and older people become demented more often than younger people, dealing with demented people is now commonplace. Declining sentience in an aging population has become one of the major changes facing 21st century societies.

Intelligence is usually approached by evaluating the results of mental (brain) processing. The memory part of intelligence may be taken for granted and the focus is often on expressive skills. In the evaluation of intelligence, we have recognized that there are underlying general functions that determine how smart a person is. Learning is based on memory and in a functional sense achievements can be described in terms of memories of different types. Four levels of memory competence can be identified during the course of a lifetime.

Peak performance is reached early and may be preserved during senescence only by rare individuals. Most humans' suffer from memory decline as they age and are considered age-appropriate if their performance remains within the range of same-age peers.  In the USA, the average performance for 30-year-olds on the Wechsler Memory Scale is 31; and the "normal" average performance for 70-year-olds is 15.  Some aging humans decline more than their same-age peers without experiencing a major disruption of daily living activities and can be described as senescent with a mild cognitive impairment. Others deteriorate more severely and memory impairment interferes with daily living and all aspects of sentience. Aging subjects have more difficulty processing visual scenes, completing complex reasoning tasks, and have a lower capacity working memory showing more difficulty keeping thoughts in mind for later use.

There is a variety of age-related and disease-related changes in the brain that cause dementias and the manifestations include a range of disabilities. Obesity and diabetes 2 increase the incidence of dementia which is linked to the risk factors that increase arterial disease. In a study of 10,276 men and women who were followed on average for 27 years 713 (6.9%) participants were diagnosed with dementia. Compared with the dementia risk in people of normal weight, risk of dementia was increased by 74% in obese people and by 35% in overweight people. 

While dementia is associated with increasing age, loss of intelligence can occur at any age for a variety of reasons. Autism in young children and schizophrenia in adolescents and young adults, for example, are early patterns of dementia. Laura Helmuth summarized findings reported at a Symposium on Neuroscience, Aging, and Cognition:   “By some measures brain function appears to decline as we age. Behavioral studies have shown, for example, that older people are slower on easy tasks and less accurate on difficult ones; their memories are leaky; they're easily distracted in tests of attention… researchers have increasingly been using imaging techniques. Some researchers have observed that certain brain areas physically shrink over time, whereas others have found that the patterns of neural activity in 60- or 70-year-olds often bear little resemblance to those in the 20-something subjects who populate most brain functional imaging studies… “

The occipital cortex appears to be the best preserved with aging, but the prefrontal cortex shrinks by about 5% per decade between the ages of 20 and 80. The hippocampus, after age 45, loses about 7% of its volume per decade. Elderly subjects tended to use more bilateral brain processing with more frontal lobe activity than younger subjects.

Exercise reduces age related dementia. Exercise improves metabolism, cardiovascular function and increases brain blood flow. Exercise involves whole brain activity and whole brain activity releases growth factors that maintain, if not increases healthy neuronal networks.

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Human Brain in Health and Disease

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The Human Brain in Health and Disease, 2010, is a Persona Digital Book. We encourage readers to quote and paraphrase topics from Human Brain in Health and Disease published online and expect proper citations to accompany all derivative writings. The author is Stephen Gislason and the publisher is Persona Digital Publications. The date of publication is 2010. The URL to the book description is Human Brain