Dementia was known to human society since antiquity. Old men and women who survived the illnesses and adversities of the many years they lived, lost the sharpness of mind with age when their memory and intellect deteriorated. This was considered as a normal unavoidable part of the aging process. Many historical records tell of stories of famous men who lost their mental capacity in old age.

This loss of proper judgement and intelligence in advanced age was seen as the reverse of rise of intellect from the ignorance and foolishness of childhood. Mental abilities were going back a full cycle to weakness of early childhood, similar to the decline in physical abilities. According to a Greek Philosopher, Pythagoras who lived in Athens in the 7th century BC, human lifespan goes from one phase to another. Infancy proceeds to adolescence and young adulthood, then middlle and old age, ending in death. Old age was given the name "senium" which is a period of decline in mental and physical power. Life come to a close with the unfortunate period when the mind is reduced to "infant-like imbecility" according to him.

Other philospohpers in Athens, Aristotle and Plato, also spoke of the mental decay of advanced age. Still thinking of it as an inevitable process that affects all old men, and which nothing could prevent. This prejudice against the elderly is clear in statement of Plato that the elderly were unsuited for any position of responsibility because they lose the sharpness of the mind that characterises the youth. Characteristics like judgement, imagination, power of reasoning, and memory were thought to diminish with advance of age which is far from true. Ageism as we call it nowadays is inherited from many centuries in the past. What we know now is that only a fraction of those over 65 may suffer from true dementia (only 5%). It is probable that this view stems from the inability to distingiush dementia as such from other causes of decline in mental abilities in old age such as physical and other mental conditions. We do know that depression is much more prevalent in old age, as well as the decline in hormones, both may contribute to deterioration in mental performance.

This remained the accepted view until the 19th century, as a broader concept of dementia remained the rule. Dementia meant any mental illness in old age which affect the psychosocial capacity, including reversible physical conditions and even mental illness such as depression or schizophrenia. Anyone who lost his ability to reason and good judgement was labelled "demented", and this was applied to mental conditions like psychosis or physical nervous illness like syphilis which causes damage to the nervous system and the brain. At those earlier times, nothing was known about the hardening of the arteries because of excess of animal fat consumption("High cholesrol") or "high blood pressure" which contributed to vascular changes in the brain manifesting as vascular dementia.

Intelligent minds like that of the Roman statesman and philospher Cicero grasped that this is not always true. He held a view similar to our understanding today that loss of mental function was not inevitable in the elderly. He spoke of how those who remained mentally active and eager to learn new things in old age and that mental activity could actually avert dementia . Physicians during the Roman Empire, like Galen and Celsus, ignored these progressive views of Cicero as the medical profession and science was dominated by the teachings of Aristotles.

Physicians sometimes wrote of dementia. Special hospitals housed those diagnosed with dementia or insanity, but no distiction was made between the two. Little was recorded about dementia in Western Medical books apart from the Aristotelian view hundreds of years. Enlightment philosopher like Roger Bacon viewed old age as a punishment for the original sin, and dementia was inevitable.

Literature and drama reffered to loss of mental ability in old age. William Shakespeare allluded to it in King Lear.

Only during the 19th century, when examination of the tissues of the deceased bodies was performed, doctors came to conclusion that elderly dementia was the result of cerebral atherosclerosis either due to blockage of the major arteries supplying the brain or small strokes within the vessels. However, all dementias was attributed to this.

In 1906,Dr. Alois Alzheimer, a German psychiatrist and neurologist, described a middle-aged patient who had symptoms of progressive dementia that affected her language, memory, and behavior. After the patient's death at the age of 55, Alzheimer extract some of the brain of that patient and examined it under the microscope. He applied new techniques to stain the brain tissue so the structure of the brain cells would appear clear. In the patient's brain tissue he discovered the presence of tangled fibres and patches of deposits not known to be a normal structure of the healthy brain. These deposits are now termed "neurofibrillary tangles" and "neuritic plaques" as they are the remains of dead nerve cells (neurones). These tangles and plaques were more evident in the outer layers of the brain: the area known as the neocortex.

Some plaques and tangles occurred in elderly persons without dementia, and some elderly persons with dementia had few plaques and tangles. Alzheimer thought that the newly discovered disease was a presenile dementia. In the late 1960s, new studies found that the degree of dementia correlated with the number of neuritic plaques in the brain cortex. Other causes of senile dementia were also recognized

Alzheimer's disease was thought to be rare in people below 65 years of age as the first patient was in her fifties. This became the established view until 1960s when dementia of Alzheimer type has been proved as the predominant cause of cognitive decline in old age and one of the neurodegenrative diseases. Vascular dementia was established as rarer compared to Alzhiemer's disease which is a major cause of mental deterioration in old age. Mixture of both conditions may occur in many patients.

It was in 1976, when a neurologist Robert Katzmann suggested a link between senile dementia and Alzheimer's disease. Katzmann suggested that senile dementia is identical with Alzheimer's disease under the microscope and therefore should not be treated differently. Alzheimer's disease is actually common, and was the fourth- or 5th-leading cause of death.

The chance of developing Alzhiemer's disease increases with age. Of those over 65 years, 5% of this group develop it. This increases to 10% in the 75-year-olds and as many as 40-50% in 90-year-olds group are affected. Many individuals over 100 years do not show notable cognitive impairment. Some doctors suggest that if you pass the 85 without developing dementia, you have a lower chance of developing it. A larger percentage of dementia cases are women, may be because of their longer overall lifespan.

Diseases of old age were rare before the last century. People rarely lived beyond 60, after all life expectancy at birth was 35 years before the era of modern medicine. Old age diseases, including dementia were rare or neglected as natural process not in need of treatment. More and more people now live beyond 80 which made the problem of dementia more prominent. The number of people over 65 started rapidly climbing. Before World War II, elderly population over 65 represented 5% of the polulation. This has doubled in many countries and increased four times (20%) in Germany and Japan. Many celebrities have been diagnosed with Alzhiemer's disease and made it public, including movies stars, novelists, musicians and even the former US president Ronald Reagan.

Nowadays, we have the tools to diagnose Alzhiemer's disease and identify the various types of dementia. Alzheimer's disease and vascular dementias are the most common types. Examination of brain tissues under the microscope post-mortem, symptoms and history from family are used,as well as, measuring brain metabolic activity in nuclear medical imaging tests such as SPECT and PETscans of the brain. It is important to differentiate the type of dementia as various forms have different outcomes and causes. Sometimes, the cause of dementia can be managed like in the case of vascular dementia where reducing the chance of hardening of the vessels and avoiding further clots may reduce the speed of the progression of the illness.