"Blocking-like" effects in attentional set-shifting: Redundant cues facilitate shifting in male rats with medial prefrontal cortex inactivation

Without a functioning prefrontal cortex, humans and other animals are impaired in measures of cognitive control and behavioral flexibility, including attentional set-shifting. However, the reason for this is unclear with evidence suggesting both impaired and enhanced attentional shifting. We inhibited the medial prefrontal cortex (mPFC) of rats while they performed a modified version of an attentional set-shifting task to explore the nature of this apparent contradiction. Twelve adult male Lister hooded rats received AAV5-CaMKIIa-hM4D(Gi)-mCherry viral vector bilaterally into mPFC to express inhibitory 'Designer Receptors Exclusively Activated by Designer Drugs' (iDREADDs). The receptors were activated by systemic clozapine N-oxide (CNO) to inhibit mPFC function. The rats were tested in the standard attentional set-shifting task four times: twice after i.p. administration and twice after oral administration of vehicle or CNO (10 mg/kg). They were then tested twice in a modified task, with or without oral CNO. The modified task had an extra stage before the extradimensional shift, in which the relevant exemplars remained relevant and new exemplars that were fully predictive but redundant replaced the previous irrelevant exemplars. These exemplars then became relevant at the subsequent ED stage. In the standard task, mPFC inactivation impaired attentional set-shifting, consistent with previous findings. However, in the modified task, mPFC inactivation abolished ED shift-costs. The results support the suggestion that the mPFC is needed for the downregulation of attention that prevents learning about redundant and irrelevant stimuli. With mPFC inactivated, the rat learns more rapidly when previously redundant exemplars become the only relevant information.