Neural activity in the human brain signals logical rule identification

To select an appropriate action, we conform to a behavioral rule determined uniquely in each behavioral context. If the rule is not predetermined and must be discovered, we often test hypotheses concerning rules by applying one candidate rule after another. The neural mechanisms underlying such rule identification are still unknown. To explore which brain areas are involved in the process of logical rule identification and to determine whether such areas differ from those taking part in implementing the rule to find a suitable action, we measured brain activation using functional magnetic resonance imaging while subjects performed a rule-identification task. The subjects were required to select a red or blue square on a screen based on either a "sequence rule" or a "probability rule." Positive or negative feedback to the subject's choice led the subject to identify the correct rule. We found that the posterior medial frontal cortex (pMFC), caudate nucleus, fusiform gyrus, and middle temporal cortex exhibited significant activation during the period when subjects underwent the hypothesis testing. Among these brain areas, the pMFC and caudate nucleus were also activated in response to the critical feedback signals selectively during the trials when the subjects identified a rule. Furthermore, we found a significant enhancement in effective connectivity between the active regions in the pMFC and caudate regions.