Neuronal loss in old people: the effects of ageing or disease?

There is abundant evidence to show that the brains of many persons, who do not suffer from overt neurological or psychiatric disease, deteriorate in structure in old age. However, it still remains uncertain as to whether these changes stem from the effects of an ageing process per se or whether the simply reflect the minor pathological results of clinically incipient disorders such as Alzheimer's disease or Parkinson's disease (conditions which become increasingly widespread in later life) or the cerebral manifestations of systemic disease.