Influences of the rearing conditions on functional properties of the rat's prefrontal system

For a period of 42 days, starting on their 22nd day of life, rats were housed either in an 'enriched' maze-like environment in which acquisition of food and water was occasionally conditioned upon solution of spatial problems, or under 'impoverished' conditions with minimal stimulation and food and water always available. The animals were subsequently tested for initial acquisition and retention of spatial delayed alternation and a visual pattern discrimination. Finally, the effect of ablation of the medial prefrontal cortical area on the performance of the two tasks was investigated. The results showed an interaction between the rearing conditions and the order of the task presentation: the enriched environment clearly affected performance in the first task only. Thus, the group which started with delayed alternation was better in this task than any other group: the group which started with the visual discrimination performed worse in that task than any other group. The rearing conditions seemed to have no effects on the degree of impairment produced by a prefrontal cortical lesion. It is suggested that the presently used enriched environment initially biases the rats towards application of spatial hypotheses during problem solving behaviour and against the use of a visual hypothesis.