[Structural changes in normal aging of the brain].

During normal ageing of the brain its weight and volume decrease significantly and the ventricles of the brain enlarge. The number of neurons of the brain stem in some areas does not decline, in the neocortex the number of neurons declines during the period between the age of 24 and 100 years by a maximum of 10-15%. As to neurotransmitting systems, the numeric atrophy during ageing affects mainly the noradrenergic locus coeruleus and the dopaminergic substantia nigra; the cholinergic n. basalis is probably not affected. The main change which takes place in neurons during ageing is their diminution. Dendritic systems of neurons undergo during ageing regressive as well as progressive changes; in some areas progressive changes predominate, in others regressive ones, in some areas both types of changes are in equilibrium. During ageing in neurons the nucleoli diminish at a varying rate. From this it is concluded that protein synthesis is altered and there is an increase of lipofuscin; both these changes take place in different ways in different neuronal populations, similarly as the diminution of Nissl's substance. The relationship of Alzheimer's disease and ageing of the brain is obscure from the pathogenetic aspect; there exist statistically significant but only quantitative differences. No evidence was provided that ageing of the brain per se is the cause of dementia.