Neural Correlates of Abstract Rule use within the Rostro-Caudal Axis of the Frontal Lobes

Abstract

This paper presents 2 experiments aimed to address key limitations in the understanding of how abstract rules (i.e., matching, non-matching) are subserved by regions of the prefrontal cortex (PFC) and frontal lobes of the brain. A number of previous investigations have demonstrated convergent findings that the frontal lobes of the brain exhibit a functional hierarchy, in which increasingly abstract rules are associated with more rostral neuronal activations along a rostro-caudal axis (Badre and D’Esposito, 2007, 2009; Bunge and Zelazo, 2006; O’Reilly, 2010). However a recent investigation by Crittenden and Duncan (2014) has suggested that increased attentional resources is associated with more rostral neural instantiations, when abstractness of the action rule is held constant. Experiment 1 assessed the validity of novel experimental manipulations, which were hypothesized to assess the independence between degrees of abstractness for action rules from that of the difficulty associated with the implementation of action rules. Experiment 2 implemented variants of these tasks during functional magnetic resonance imaging (fMRI) data acquisition. The results indicate that rule difficulty, via increased stimulus sets and memory load, bears important implications for the supposed functional arrangement of the rostro-caudal axis of the frontal lobes, specifically within the dorsolateral PFC. Findings from these experiments contribute to a better understanding of the functional arrangement of neural substrates within the frontal lobes.