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.

The personality trait self-directedness predicts the amygdala's reaction to appetizing cues in fMRI.

Personality and neural response to food cues in various mesolimbic brain structures have been linked to eating disorders. We investigated the question of whether personality traits in healthy individuals correlate with the brain activation induced on confrontation with appetizing visual stimuli. Personality was assessed in 27 normal-weight participants (14 women, mean age=26.0, SD=3.3 years) with the Temperament and Character Inventory (TCI). After an overnight fast, participants viewed blocks of pictures, half containing appetizing food and the other half showing scrambled pictures as control. After each block, participants rated their appetite. Brain activation was measured using a 3T MR scanner. Food compared to control stimuli elicited a significantly higher appetite rating, as well as strong activation in the ventral and dorsal visual stream, the fusiform gyrus and consecutive limbic centres such as the parahippocampal gyrus, the amygdala, the thalamus, the insula, the ventral striatum and the orbitofrontal cortex. In a region-of-interest analysis, the TCI trait self-directedness was negatively correlated with mean blood oxygenation level dependent (BOLD) signal change in the right amygdala (r=-.43, p=.025). Ultimately, amygdala reactivity might provide a risk factor for the development of eating disorders.