SEPARATION OF ASSOCIATIVE FROM NON-ASSOCIATIVE SHORT LATENCY CHANGES IN MEDIAL GENICULATE AND INFERIOR COLLICULUS DURING DIFFERENTIAL CONDITIONING AND REVERSAL IN RATS

Results obtained in a recent experiment in this laboratory drew attention to the possible contribution of subtle non-associative processes to changes in the early latency unit responses obtained in MGB and IC of the rat during the learning of a differential appetitive conditioning task. An important possible source of such non-associative effects was shown to arise from differences in the interval between a previous food pellet presentation and the following CS+ or CS-. To determine whether previously reported changes in MGB and IC were due to associative processes or to non-associative ones, the present experiments were carried out using a counterbalanced stimulus presentation schedule which placed the CS+ and CS- at the same average time following a previous food pellet. Criteria adopted for characterizing a change as associative required that the response to the CS+ be enhanced relative to that to the CS- throughout repeated reversal sessions. The results obtained support previous findings of early latency associative changes in MGB, and are consistent with the idea that such changes are most likely to occur in the medial division of this nucleus. The findings in the IC thus far do not support the notion that this nucleus participates in this process. However, in view of the complex structure of the IC and the fact that not all of its subdivisions were sampled, these negative findings must be viewed with caution. The results also support the view that the anatomical distribution of neurons participating in the elaboration of associative changes may be more restricted than that of neurons participating in non-associative ones. © 1979.