The term dementia, as used in diagnostic contexts, refers to the decline and loss of cognitive function (for example, short-term and long-term memory, attention, executive function and reasoning) that may accompany a wide and complex range neurodegenerative diseases such as Alzheimer's disease, Lewy Bodies Diseases (for example, Parkinson's), demyelinating diseases (for example, Multiple Sclerosis) or conditions such as alcoholism and HIV (AIDS). This is different from the effects of treatment such as chemotherapy on the brain (resulting in this case in chemo brain).
Dementia is best understood in terms of the severity of its consequences which can interfere with daily living in a manner which, depending on the condition, may progress from mild to moderate and from moderate to severe. An operative division of dementia into those three levels of severity is offered by the World Health Organization (WHO), for use by professional neurodiagnosticians. To determine the level of severity in dementia, neurodiagnosticians use neurocognitive evaluations, scales and interview the patients and their relatives. The three levels of severity are described below.
First Level - Mild dementia: The person is capable of performing familiar, rehearsed daily activities and continues to live independently. Nevertheless, cognitive difficulties are apparent, especially when dealing with recent needs, for example, in paying attention to and remembering where possessions have recently been placed, what the time and place for new social appointments are or what information was recently relayed.
Second Level - Moderate dementia: Memory loss has become so severe that the person has lost the ability to live independently. Only the most familiar and most automatic routines are retained. Novel information is retained for the shortest of spans, sometimes a few seconds. The person cannot remember information about his own identity, place of residence, activities just carried out and the names of the family members.
Third Level - Severe dementia: Memory loss, both verbal and non-verbal, is so widespread that the person cannot remember any novel information. Except for tiny remaining particles, all previously known information has been forgotten. The subject fails to recognize even close family members.
Why some people experience the neurobiological pathology of dementia as well as its tragic consequences while others, with the same neurobiological pathology, exhibit none of the tragic consequences but continue to lead an autonomous, self-sufficient life, is one of the most mind-puzzling mysteries of the 21st century.
Cognitive reserve, the knowledge accumulated through one's continued learning, seems to play an important role in coping with the advent of dementia. Continued new learning teaches the brain to modify its neural activity in order to cope with the challenge occasioned by the new learning situation. Therefore, learning a new skill (to dance, to draw, to speak a new language, to play an instrument) or training untapped cognitive functions, for example, through cognitive brain training, gives the brain the adaptability it needs to rethink and rewire its neural circuits into new ones when faced with the challenges posed by dementia.