Right ventrolateral prefrontal cortex mediates individual differences in conflict-driven cognitive control

Abstract

Conflict adaptation--a conflict-triggered improvement in the resolution of conflicting stimulus or response representations--has become a widely used probe of cognitive control processes in both healthy and clinical populations. Previous fMRI studies have localized activation foci associated with conflict resolution to dorsolateral PFC (dlPFC). The traditional group analysis approach employed in these studies highlights regions that are, on average, activated during conflict resolution, but does not necessarily reveal areas mediating individual differences in conflict resolution, because between-subject variance is treated as noise. Here, we employed a complementary approach to elucidate the neural bases of variability in the proficiency of conflict-driven cognitive control. We analyzed two independent fMRI data sets of face-word Stroop tasks by using individual variability in the behavioral expression of conflict adaptation as the metric against which brain activation was regressed while controlling for individual differences in mean RT and Stroop interference. Across the two experiments, a replicable neural substrate of individual variation in conflict adaptation was found in ventrolateral PFC (vlPFC), specifically, in the right inferior frontal gyrus, pars orbitalis (BA 47). Unbiased regression estimates showed that variability in activity in this region accounted for ∼ 40% of the variance in behavioral expression of conflict adaptation across subjects, thus documenting a heretofore unsuspected key role for vlPFC in mediating conflict-driven adjustments in cognitive control. We speculate that vlPFC plays a primary role in conflict control that is supplemented by dlPFC recruitment under conditions of suboptimal performance.

Figure 1

Example stimuli and individual variation in the expression of the conflict adaptation effect (the differential in the congruency effect following an incongruent as compared to a congruent trial) are shown for Experiment 1 (a, c), and Experiment 2 (b, d). In c and d, each individual subject’s conflict adaptation score (in ms) is shown as a circle, with solid lines marking zero conflict adaptation, and dashed lines marking the mean conflict adaptation score for each sample. Positive values reflect reduced interference following an incongruent compared to a congruent trial, that is, successful conflict adaptation.

Figure 2

(a, b) Experiment 1 neuroimaging results for a whole-brain search for voxels displaying a positive correlation between conflict-driven neural activity and behavioral conflict adaptation scores, as defined by the previous × current trial congruency interaction term ([CI – CC] – [II – IC]) (a), or as defined by the relative speed-up on incongruent trials only (CI – II) (b), are shown on sagital and axial slices (left panels), and rendered (right panels), on a normalized brain (voxelwise height threshold = P < 0.005, cluster extent threshold > 21 voxels). (c) Unbiased regression estimate (see Methods) of the association between inter-subject variability in behavioral conflict adaptation ([CI – CC] – [II – IC]) (y-axis) and conflict-driven activity in the right ventrolateral prefrontal cortex (vlPFC, x-axis).

Figure 3

(a, b) Experiment 2 neuroimaging results for a whole-brain search for voxels displaying a positive correlation between conflict-driven neural activity and behavioral conflict adaptation scores are, as defined by the previous × current trial congruency interaction term ([CI – CC] – [II – IC]) (a), or as defined by the relative speed-up on incongruent trials only (CI – II) (b), are shown on sagital and axial slices (left panels), and rendered (right panels), on a normalized brain (voxelwise height threshold = P < 0.005, cluster extent threshold > 35 voxels). (c) Unbiased regression estimate (see Methods) of the association between inter-subject variability in behavioral conflict adaptation ([CI – CC] – [II – IC]) (y-axis) and conflict-driven activity in the right ventrolateral prefrontal cortex (vlPFC, x-axis).