Bending the rules: strategic behavioral differences are reflected in the brain.

The implementation of higher-order conditional motor behavior was investigated in the present fMRI study with the objective of answering three questions: (a) what happens in situations where one stimulus dimension alone does not sufficiently determine the correct response?; (b) does the implementation of second-order stimulus-response (S-R) rules on the basis of matching (congruent) or nonmatching (incongruent) S-R associations differ from the implementation of congruent and incongruent first-order S-R rules?; and (c) is the cerebral implementation of second-order rules influenced by interindividual behavioral differences arising from the use of different strategies? The findings indicate that several cortical areas were more strongly engaged for second-order rules. More specifically, rule integration based on a rule match led to enhanced activation in posterior parietal cortex, whereas rule integration based on a rule mismatch was associated with enhanced activation in dorsal premotor cortex and left rostrolateral prefrontal cortex. Interindividual strategy differences were revealed by strikingly different behavioral data patterns: One subgroup of participants displayed strong congruency effects for second-order rules, whereas another subgroup displayed nonsignificant or even reversed congruency effects. Importantly, these strategy differences strongly modulated the cerebral implementation of second-order rules based on a rule mismatch. Together, the present findings reveal differential brain activation patterns for higher-order S-R rules depending on rule congruency and interindividual strategy differences. Moreover, they emphasize the necessity of taking interindividual behavioral differences into account when investigating the cerebral implementation of cognitive processes even in rather simple and well-controlled experimental paradigms.