Origins of anthropoid intelligence IV. Role of prefrontal system in delayed alternation and spatial reversal learning in a conservative eutherian (Paraechinus hypomelas).

A conservative eutherian mammal (the hedgehog, Paraechinus hypomelas) was tested on delayed alternation performance and spatial reversal learning before and after ablations of the prefrontal cortex. The anatomical results show that the cortical focus of the projections of the medial dorsal nucleus, the prefrontal cortex, does not include the neocortex on the dorsal convexity of the hedgehog's frontal lobe but, instead, the perirhinal and pregenual neocortex immediately surrounding the frontal convexity. The behavioral results show that normal performance of hedgehogs on these two behavioral tests depends upon the integrity of their prefrontal cortex, but not on the integrity of their frontal convexity or olfactory bulbs. The similarity in the results obtained from prefrontal hedgehogs and a divergent variety of other species with prefrontal ablations indicates that the role of the prefrontal system in the abilities measured by these two tests is at least as old as Eutheria and, thus, probably imposed persistent constraints on subsequent evolutionary modifications of the prefrontal system.