Ageing of the brain.

The brains of individuals who are cognitively normal show age-related changes that include an overall reduction in the brain volume and weight and enlargement of the brain ventricles. These changes are partly the result of nerve cell loss but accurate estimates of neuronal loss are notoriously difficult to make. There is loss of synapses and dendritic pruning in the aged brain but in selected areas rather than globally. Neurofibrillary tangles and senile plaques are the neuropathological hallmark of Alzheimer's disease in which they are more abundant and widespread than in the brains of intellectually intact elderly people. Alzheimer's disease has, therefore, been regarded as accelerated brain ageing, however, since there is a strong genetic contribution to developing the disease it implies that it may not be the inevitable, even if frequent, consequence of old age. The interplay between genetic and environmental factors probably determines the degree of pathological brain ageing and whether or not individuals develop dementia.