To work or not to work: Neural representation of cost and benefit of instrumental action.

By definition, instrumental actions are performed in order to obtain certain goals. Nevertheless, the attainment of goals typically implies obstacles, and response vigor is known to reflect an integration of subjective benefit and cost. Whereas several brain regions have been associated with cost/benefit ratio decision-making, trial-by-trial fluctuations in motivation are not well understood. We review recent evidence supporting the motivational implications of signal fluctuations in the mesocorticolimbic system. As an extension of "set-point" theories of instrumental action, we propose that response vigor is determined by a rapid integration of brain signals that reflect value and cost on a trial-by-trial basis giving rise to an online estimate of utility. Critically, we posit that fluctuations in key nodes of the network can predict deviations in response vigor and that variability in instrumental behavior can be accounted for by models devised from optimal control theory, which incorporate the effortful control of noise. Notwithstanding, the post hoc analysis of signaling dynamics has caveats that can effectively be addressed in future research with the help of two novel fMRI imaging techniques. First, adaptive fMRI paradigms can be used to establish a time-order relationship, which is a prerequisite for causality, by using observed signal fluctuations as triggers for stimulus presentation. Second, real-time fMRI neurofeedback can be employed to induce predefined brain states that may facilitate benefit or cost aspects of instrumental actions. Ultimately, understanding temporal dynamics in brain networks subserving response vigor holds the promise for targeted interventions that could help to readjust the motivational balance of behavior.

Neural correlates of the volitional regulation of the desire for food.

OBJECTIVE: In this study, we investigate the brain mechanisms of the conscious regulation of the desire for food using functional magnetic resonance imaging. Further, we examine associations between hemodynamic responses and participants' cognitive restraint of eating (CRE), as well as their susceptibility to uncontrolled eating. SUBJECTS: Seventeen non-vegetarian, right-handed, female Caucasian participants (age: 20-30 years, mean 25.3 years±3.1 s.d.; BMI: 20.2-31.2 kg m(-2), mean 25.1±3.5 s.d.). MEASUREMENTS: During scanning, our participants viewed pictures of food items they had pre-rated according to tastiness and healthiness. Participants were either allowed to admit to the desire for the food (ADMIT) or they were instructed to downregulate their desire using a cognitive reappraisal strategy, that is, thinking of negative long-term health-related and social consequences (REGULATE). RESULTS: Comparing the hemodynamic responses of the REGULATE with the ADMIT condition, we observed robust activation in the dorsolateral prefrontal cortex (DLPFC), the pre-supplementary motor area, the inferior frontal gyrus (IFG), the dorsal striatum (DS), the bilateral orbitofrontal cortex (OFC), the anterior insula and the temporo-parietal junction (TPJ). Activation in the DLPFC and the DS strongly correlated with the degree of dietary restraint under both conditions. CONCLUSION: Cortical activation in the DLPFC, the pre-supplementary motor area and the inferior frontal gyrus (IFG) are known to underpin top-down control, inhibition of learned associations and pre-potent responses. The observed hemodynamic responses in the lateral OFC, the DS, the anterior insula and the TPJ support the notion of reward valuation and integration, interoceptive awareness, and self-reflection as key processes during active regulation of desire for food. In conclusion, an active reappraisal of unhealthy food recruits the brain's valuation system in combination with prefrontal cognitive control areas associated with response inhibition. The correlations between brain responses and CRE suggest that individuals with increased cognitive restraint show an automatic predisposition to regulate the hedonic aspects of food stimuli. This cognitive control might be necessary to counterbalance a lack of homeostatic mechanisms.