Mentat. Aspects of AcxEINO .35 



many of the most important wc cannot measure; study of 

 animals takes us only a little way; and we cannot control 

 some variables wliieli are probably powerful influences upon 

 the rate and signs of mental ageing in human beings. Conse- 

 quently we are deprived of many of the methods which are 

 available for separating pathological from normal in the 

 somatic features of old age. 



It might be said that these difficulties can evidently be 

 overcome, since they have been overcome at the other end of 

 life. To some extent that is true. We know a great deal about 

 mental changes in children as they develop, but in them also 

 the difficulty of telling what is pathological may arise in 

 matters of emotion and behaviour, as the experience of every 

 child guidance clinic attests. In any case ageing is spread 

 over a longer period than childhood is, its timing and form 

 are probably less ordained in advance by heredity, and the 

 strong environmental influences that may play upon it are 

 harder to control for purposes of investigation. Hence the 

 greater obstacles in studying its normal character. 



If we could relate the normal mental characteristics of old 

 age to structural changes in the ageing brain, we might be 

 better off. This we cannot do. Such changes occur, of course, 

 but have been very little studied in the normal. The only 

 thorough examination of cerebral changes in normal old age, 

 uncomplicated by dementia, is Gellerstedt's, which was 

 carried out on 50 brains. His careful findings lead to a dead 

 end, so far as the relating of cellular to psychological phen- 

 omena goes. Thus, speaking of senile plaques, he says, 

 "Manchen andern Autoren beistimmend, konnen wir als 

 unsere Auffassung aussprechen dass diese Gebilde, ob nicht 

 oder ob in grossen Mengen vorhanden, durchaus keine siehere 

 Aussage iiber den vorhergehenden psychischen Zustand des 

 Patienten erlauben". Similarly Oskar and Cecile Vogt in 

 1941 compared the minute structure of the thalamus in the 

 brains of four distinguished old scholars who had preserved 

 their intellectual faculties till their death with those of men 

 who had died in senile dementia: they concluded that the 



