Alleviation of overtraining reversal effect by transient inactivation of the dorsal striatum.

In this study, we investigated the role of the dorsal striatum in the acquisition and the use (retrieval) of a specific learning developed during overtraining. The paradigm was such that rats had to respond differentially to two signals in order to obtain food or to avoid an electrical footshock. Overtraining was aimed at eliciting a facilitative effect on discrimination reversal as compared to simply trained rats. In this way, transient inactivation of the dorsal striatum by lidocaine enabled us to investigate, separately, the role of this structure during overtraining and reversal. The data show that inactivating the dorsal striatum before each reversal session prevented the overtraining reversal effect observed in control rats. Moreover, inactivation of the dorsal striatum during overtraining had no effect on the level of discriminative performance just as it did not affect the subsequent facilitative effect on reversal. These results show that even though the striatum might normally be part of a routine automatic system, clearly its contribution is not essential. Indeed, despite inactivation of the striatum in overtrained rats, their ability to develop an efficient selection process that can be used during reversal was observed. However, the integrity of the striatum became essential in order to mediate the modification of behaviour when this behavioural routine formed during overtraining had to be modified during reversal.