Subcortical nature of Pavlovian differentiation in the rabbit.

Normal, hemidecorticated and decorticated rabbits were trained to criterion in a Pavlovian light-tone differentiation situation using the nictitating membrane preparation. Neither hemidecortication nor total neodecortication had any significant effect on the acquisition of Pavlovian conditional responses and both types of lesion were accompanied by differentiation performance which was as good as, or better than, that shown by normal controls. There was an indication however, that total neodecortication produced a slight retardation in the initial acquisition of conditional responses to the positive conditional stimulus. Both hemidecortication and bilateral neodecortication increased conditional response onset latencies but did not affect unconditional response latencies. These data are consistent with the notion that the essential substrate for Pavlovian conditioning is subcortical and that the breadth of stimulus feature extraction is reduced by neodecortication. In the course of this study it was noted that neodecortication reduced the asymptotic body weight of animals in both the lesioned groups.