Rule-guided behaviour: how and where rules are represented and processed in human brain

Much of our behaviour is guided by rules defining associations between meaningful stimuli and proper responses. The ability to flexibly switch between rules to adapt to a continuously changing environment is one of the main challenges for the human cognitive system. Investigating how different types and combinations of rules are encoded and implemented in human brain is crucial to understand how we select and apply rules to guide our behaviour and react flexibly to a dynamic environment. The present thesis addressed the issue of where in the brain different types of rules are represented and how they are processed. Behavioural paradigms, functional magnetic resonance imaging, and multivariate pattern classification were combined to shed light on the cognitive mechanisms underlying rule processing and to identify brain areas encoding the contents of such processes. Using a priming paradigm, the first study assessed which types of associations (conditional, disjunctive, spatial, or quantified) could be activated automatically and trigger unconscious inferences. It proved that Modus Ponens inference is carried out unconsciously. The second study demonstrated that a condition-action rule instructed on a trial-by-trial basis and immediately marked as irrelevant causes significant interference effects when involuntarily triggered by target stimuli matching the condition in the rule. In the third study, using complex rule sets, we showed that rules at different level in the hierarchy of action control are encoded in partially separate brain networks. Moreover, we found that rule information is represented in distinct brain areas when different types of rules are encoded jointly. In the fourth study, we used rules composed using different logical connectives to expand the set of associations considered and to assess possible differences in rule representation and processing between rules with distinct logical forms. We found that separate brain areas encoded task rule information during rule representation and evaluation and that the involvement of these areas depended on the specific rule active in a trial. Taken together, our results suggest that conditional rules hold a special status in the human cognitive system, contributing to our knowledge on rule-guided behaviour.