Post-trial reticular facilitation of associative changes in multiunit activity; comparison between dentate gyrus and entorhinal cortex

Multiunit activity recorded in both the dentate gyrus and the entorhinal cortex during classical conditioning was studied in freely moving rats receiving a mild post-trial stimulation of the mesencephalic reticular formation. Dentate multiunit activity progressively increased in response to an auditory signal (conditioned stimulus) after pairing the signal with a footshock (unconditioned stimulus). No such increase was seen in the entorhinal cortex of the same animals during conditioning. Post-trial reticular stimulation facilitated the development of associative changes in dentate multiunit activity, while having no effect in the entorhinal cortex. The results were interpreted as indicating a possible specificity of action of post-trial reticular stimulation on learning-induced plasticity and are discussed in relation to the concept of neural perseverance in memory consolidation.