Like the other tissues of the body, human nerve tissue ages year by year with the increment of age. As a natural regular rule, it begins with embryonic period, passes through childhood, adolescence, adult stage and geratic period and finally becomes feeble and dies. This regularity manifests itself not only in tissue structure but also in tissue functions. It can, therefore, be regarded that dementia of old people is an unevitable stage in the course of natural development, except for the considerable interhuman individual difference in degree of aging of the brain, which differs with different influences of internal and external factors, occurring early or lately, severely or mildly. An aged man with hypomnesis and paraphasia is always regarded as an old muddle-headed fellow by the people around him, he is never thought to be ill with disease and by no means sent to a hospital for medical advice. Understanding of senile dementia due to aging of the brain started with 1906. Clinically, the natural course of aging of the brain is marked by reduced water content in brain tissue, atrophy of brain tissue to some extent, enlarged space between cranial bone and cerebral cortex on CT encephalogram, broaden cerebral sulci and possible reduction, to some extent, in number of nerve cells of cerebral cortex. These changes are inevitable phenomena after middle age and should not be regarded as diseases of the brain.
Alzheimer's syndrome, on the other hand, does not necessarily and absolutely exist in
old people, senile dementia of Alzheimer's

Author's unit :Guangdong Gaoming Medical and Medicinal Institute of Encephalopathy, Gaoming, Guangdong 528500
type occurs with pathological changes of intracerebral neuritic spots or neurofibrillary tangles in population of any age group. An old man aged 65 or over with such clinical manifestations as amnesia , strange
temperament, behaviour disorder, retardation of reaction and hypomnesis cannot be simply regarded as having Alzheimer's syndrome, only in the presence of pathological changes of intracerebral neuritic spots or neurofibrillary tangles at autopsy can the disease be diagnosed as Alzheimer's syndrome.
Neurofibrillary tangles is one of neurofibrillar degeneration. Degeneration of neurofibrils is divided by some into three types according to the degree of damage: neuritic spots, neurofibrillary tangles and neuropil. Of the three types, the neurofibrillary tangles belongs to a representative degeneration of neurofibrils. Neurofibrillary tangles, a structural change in cytoplasm of neurons, may occur in cell body, axon and dendrite. At first, Alzheimer pointed out that the so-called degeneration of neurofibrils referred to the aggregation of argentaffine nerve fibers in neurons of patients with senile dementia and held that the quantity of neurofibrillary tangles was closely related to the degree of dementia, this direct-proportion relationship between the two was later supported by relevant data.
Neuritic spots and neurofibrillary tangles have been regarded as characteristic pathological changes of Alzheimer's disease but not specific changes. Up to now no more accurate diagnostic methods and criteria are availalble for the diagnosis of Alzheimer's syndrome. Recent studies show that both neurofibrillary tangles and neuritic spots are related to amyloid degeneration. A large number of molecular neurobiologic studies on amyloid and its pro-protein in recent years made many important findings, and we may expect a new breakthrough in this respect in the near future.