Motivated cognitive control: reward incentives modulate preparatory neural activity during task-switching

Abstract

It is increasingly appreciated that executive control processes need to be understood in terms of motivational as well as cognitive mechanisms. The current study examined the impact of performance-contingent reward incentives (monetary bonuses) on neural activity dynamics during cued task-switching performance. Behavioral measures indicated that performance was improved and task-switch costs selectively reduced on incentive trials. Trial-by-trial fluctuations in incentive value were associated with activation in reward-related brain regions (dopaminergic midbrain, paracingulate cortex) and also modulated the dynamics of switch-selective activation in the brain cognitive control network. Within lateral prefrontal cortex (PFC), both additive (inferior frontal junction) and interactive [dorsolateral PFC (DLPFC)] incentive effects were observed. In DLPFC, incentive modulation of activation predicted task-switching behavioral performance, but with hemispherically dissociable effects. Furthermore, in left DLPFC, incentive modulation specifically enhanced task-cue-related activation, and this activation in turn predicted that the trial would be subsequently rewarded (because of optimal performance). The results suggest that motivational incentives have a selective effect on brain regions that subserve cognitive control processes during task-switching and, moreover, that one mechanism of effect might be the enhancement of cue-related task preparation within left DLPFC.

Figure 1.

A, Paradigm description for task-switching. On each trial, a fixation cross appeared on the screen (300 ms), followed by a task cue (400 ms), a CTI screen with a (green) fixation cross (1600 or 4100 ms), and then presentation of the target stimulus and feedback for the response (2000 ms total). The end of the trial and start of the ITI (2500, 5000, or 7500 ms, jittered) was indicated by the fixation cross changing color (red). B, Incentive cue analysis. On incentive cued trials, performance improved in single-task and mixed-task conditions, with the largest incentive benefits occurring in the mixed-task condition. Thus, incentive cue effects were largest when cognitive control demands were highest. C, Switch cost analysis. Significant switch costs were present on non-incentive trials but not on incentive trials. This attenuation of switch costs suggests that incentive motivation enhances cognitive control, specifically the flexible switching of task set or goal information.

Figure 2.

Regions of interest. The regions in red indicate the components of the CCN that showed significantly increased activation associated with task-switching. The regions in green indicate the components of the REW that showed significantly increased activation associated with reward incentives.

Figure 3.

Full-trial analyses illustrating time course of activation during single-task and task-switching trials under incentive versus non-incentive conditions. A, Right DLPFC. This CCN region showed a main effect of task-switching but not incentives (left). Increased task-switching-related activity (SWT–SNG) in this region is correlated with reduced RT switch costs (right). B, Left DLPFC. Representative CCN region showing a task-switching × incentive × time interaction. Incentive effects on single-task trials occur only early in the trial (during incentive cue period) but persist in the mixed-block trials, suggesting a modulatory effect on control processes (left). Increased activity in this region on incentive trials during task-switching (SWT_Inc − SWT_NoInc) correlated with greater incentive-related RT facilitation (right). C, Right IFJ. This CCN region exhibited main effects of both task-switching and incentives but no interaction. D, Left dopaminergic midbrain. Representative REW region showing a main effect of incentives but no effects of task-switching. In all regions, highlighted window indicates time points (2–6) included in statistical analysis, corresponding to the primary processing period of the trial from incentive/task cue to target response, after accounting for hemodynamic lag. L, Left; R, right.

Figure 4.

A, Activity during target/feedback period. The majority of regions identified [including CCN regions such as left (L) DLPFC and REW regions such as left dopaminergic midbrain shown here] exhibited greater activity at the time of the target on incentive trials. B, Cue-related neural activity. The left DLPFC (left) exhibited greater cue-related activation in response to the processing of incentive cues compared with non-incentive cues. Regions in the REW such as the left dopaminergic midbrain (right) do not show such differences in cue-related activity. C, Trial-outcome (reward) effects during target/feedback period. Two REW regions, including the left dopaminergic midbrain (right), demonstrated increased activation specifically on rewarded incentive trials, consistent with dopaminergic effects in response to achieving performance contingent, and thus unpredictable, rewards. D, Behaviorally linked cue activity. The left DLPFC (left) exhibited greater cue-related neural activity on trials that subsequently led a rewarded outcome as a result of optimal performance. No such effects occurred on matched performance trials that were not rewarded, indicating a specific effect of the incentive cue.