Different Contribution of the Monkey Prefrontal and Premotor Dorsal Cortex in decision-making supported by inferential reasoning

Abstract Several studies reported similar neural modulations between brain areas of the frontal cortex, such as the dorsolateral prefrontal (DLPFC) and the premotor dorsal (PMd) cortex, in tasks requiring encoding of the abstract rules for selecting the proper action. Here, we compared the DLPFC and PMd neuronal activity of monkeys trained in choosing the highest-ranking image of pair (target item), selected from an arbitrarily rank-ordered set (A>B>C>D>E>F) in the context of a transitive inference task. Once acquired by trial-and-error, the ordinal relationship between pairs of adjacent images (i.e. A>B; B>C; C>D; D>E; E>F), monkeys were tested in inferring the ordinal relation between items of the list not paired during learning. During inferential decisions, we observed that the choice accuracy increased and the reaction time decreased as the rank difference between the compared items enhanced. This result is in line with the hypothesis that after learning, the monkeys built an abstract mental representation of the ranked items, where rank comparisons correspond to the item position comparison on this representation. In both brain areas, we observed higher neuronal activity when the target item appeared in a specific location on the screen, with respect to the opposite position and that this difference was particularly enhanced at lower degrees of difficulty. By comparing the time evolution of the activity of the two areas, we revealed that the neural encoding of target item spatial position occurred earlier in DLPFC than in PMd, while in PMd the spatial encoding duration was longer.