Enrichment-isolation, cortex length and the rank order effect

In a previous paper we have proposed a developmental theory to account for the neurological changes which result from differentially rearing animals in either enrichment or isolation. On the basis of brain weight measurements we suggested that the primary cause of the differential development could be traced to retarded neurological growth in the isolated animals. The present 9 studies test the generality of this theory by applying it to the cortex length changes induced in rats by differential rearing periods of between 18 and 160 days. In the light of this new data the theory has been revised to the extent that the developmental ceiling for the dependent variable is now considered to change with age instead of being fixed. Two major consequences of this revision are as follows. Firstly that the environmentally induced changes in cortical development are seen as persistent. Secondly that the Rank Order Effect is shown to be a transitory phenomenon which exists only when some, but not all of the isolate values have been restricted in their development. © 1979.