Abstract& Access to limited-capacity neural systems of cognitive control must be restricted to the most relevant information. How the brain identifies and selects items for preferential processing is not fully understood. Anatomical models often place the selection mechanism in the medial frontal cortex (MFC), and one computational model proposes that the mesotelencephalic dopamine (DA) system, via its reward prediction properties, provides a ''gate'' through which information gains access to limited-capacity systems. There is a medial frontal eventrelated potential (ERP) index of attention selection, the anterior positivity (P2a), associated with DA reward system input to the MFC for the identification of task-relevant perceptual representations. The P2a has a similar spatio-temporal distribution as the medial frontal negativity (MFN), elicited to error responses or choices resulting in monetary loss. The MFN has also been linked to DA projections to the MFC but for action monitoring rather than attention selection. This study proposes that the P2a and the MFN reflect the same MFC evaluation function and use a passive reward prediction design containing neither instructed attention nor response to demonstrate that the ERP over medial frontal leads at the P2a/MFN latency is consistent with activity of midbrain DA neurons, positive to unpredicted rewards and negative when a predicted reward is withheld. This result suggests that MFC activity is regulated by DA reward system input and may function to identify items or actions that exceed or fail to meet motivational prediction. &

IntroductIonOne-third of the US population is clinically obese (BMI ≥30 kg/m 2 ) (1), a condition associated with increased morbidity and health-care costs (2). Although the origins of this problem are complex, caloric intake in excess of expenditure is the primary cause of weight gain. Food intake is influenced by a convergence of processes in the brain, including homeostatic mechanisms, motivation, cognitive control, and decision making (3). Research has shown that obese individuals find food more reinforcing compared to healthy weight (HW) individuals (4,5). The motivational value of food can be measured by determining the extent to which an individual will work to obtain food (3) and is influenced by a variety of factors including food composition (6,7) and hunger (3).In experimental settings, obese individuals show increased food motivation, compared to HW individuals, by working more for food rewards than nonfood rewards (4) and by consuming more food in laboratory settings than individuals who demonstrate lower levels of food motivation (4,8). In addition, obese individuals, compared to overweight and HW individuals, report higher levels of eating disinhibition and hunger on the Three Factor Eating Inventory (EI) (9), which measures dietary restraint (conscious effort to control dietary intake), eating disinhibition (release of control under emotional or situational triggers), and hunger (feeling hunger and its relationship to eating) (10).Functional neuroimaging studies are beginning to examine brain mechanisms underlying food motivation. Positron emission tomography studies in HW adults, examining brain activations during food consumption, show changes in regional cerebral blood flow (rCBF) in prefrontal regions, including ventromedial prefrontal cortex (PFC), as well as insular cortical regions (11)(12)(13)(14)(15). In these studies, researchers manipulated food motivation by increasing participant hunger through fasting (4.5-36 h) and measuring responses to a liquid meal (11-13,15) or chocolate (14). rCBF increased during hungry states in the hypothalamus, insula, and the orbitofrontal cortex (11,14,15). Meal consumption was associated with increased rCBF in prefrontal regions such as the ventromedial PFC (11,13,15). It should be noted that re-analysis of rCBF results (11,13,15) using a random effects as opposed to fixed effects analysis revealed decreases rather than increases in dorsolateral prefrontal regions (16,17). One out of three adults in the United States is clinically obese. Excess food intake is associated with food motivation, which has been found to be higher in obese compared to healthy weight (HW) individuals. Little is known, however, regarding the neural mechanisms associated with food motivation in obese compared to HW adults. The current study used functional magnetic resonance imaging (fMRI) to examine changes in the hemodynamic response in obese and HW adults while they viewed food and nonfood images in premeal and postmeal states. During the premeal condition, obese participants...

Objective: To investigate the neural mechanisms of food motivation in children and adolescents, and examine brain activation differences between healthy weight (HW) and obese participants. Subjects: Ten HW children (ages 11-16; BMI o 85%ile) and 10 obese children (ages 10-17; BMI 495%ile) matched for age, gender and years of education. Measurements: Functional magnetic resonance imaging (fMRI) scans were conducted twice: when participants were hungry (pre-meal) and immediately after a standardized meal (post-meal). During the fMRI scans, the participants passively viewed blocked images of food, non-food (animals) and blurred baseline control. Results: Both groups of children showed brain activation to food images in the limbic and paralimbic regions (PFC/OFC). The obese group showed significantly greater activation to food pictures in the PFC (pre-meal) and OFC (post-meal) than the HW group. In addition, the obese group showed less post-meal reduction of activation (vs pre-meal) in the PFC, limbic and the reward-processing regions, including the nucleus accumbens. Conclusion: Limbic and paralimbic activation in high food motivation states was noted in both groups of participants. However, obese children were hyper-responsive to food stimuli as compared with HW children. In addition, unlike HW children, brain activations in response to food stimuli in obese children failed to diminish significantly after eating. This study provides initial evidence that obesity, even among children, is associated with abnormalities in neural networks involved in food motivation, and that the origins of neural circuitry dysfunction associated with obesity may begin early in life.

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BackgroundThe majority of research on obesity has focused primarily on clinical features (eating behavior, adiposity measures), or peripheral appetite-regulatory peptides (leptin, ghrelin). However, recent functional neuroimaging studies have demonstrated that some reward circuitry regions which are associated with appetite-regulatory hormones are also involved in the development and maintenance of obesity. Prader-Willi syndrome (PWS), characterized by hyperphagia and hyperghrelinemia reflecting multi-system dysfunction in inhibitory and satiety mechanisms, serves as an extreme model of genetic obesity. Simple (non-PWS) obesity (OB) represents an obesity control state.ObjectiveThis study investigated subcortical food motivation circuitry and prefrontal inhibitory circuitry functioning in response to food stimuli before and after eating in individuals with PWS compared with OB. We hypothesized that groups would differ in limbic regions (i.e., hypothalamus, amygdala) and prefrontal regions associated with cognitive control [i.e., dorsolateral prefrontal cortex (DLPFC), orbitofrontal cortex (OFC)] after eating.Design and ParticipantsFourteen individuals with PWS, 14 BMI- and age-matched individuals with OB, and 15 age-matched healthy-weight controls (HWC) viewed food and non-food images while undergoing functional MRI before (pre-meal) and after (post-meal) eating. Using SPM8, group contrasts were tested for hypothesized regions: hypothalamus, nucleus accumbens (NAc), amygdala, hippocampus, OFC, medial PFC, and DLPFC.ResultsCompared with OB and HWC, PWS demonstrated higher activity in reward/limbic regions (NAc, amygdala) and lower activity in hypothalamus and hippocampus, in response to food (vs. non-food) images pre-meal. Post-meal, PWS exhibited higher subcortical activation (hypothalamus, amygdala, hippocampus) compared to OB and HWC. OB showed significantly higher activity versus PWS and HWC in cortical regions (DLPFC, OFC) associated with inhibitory control.ConclusionIn PWS compared with obesity per se, results suggest hyperactivations in subcortical reward circuitry and hypoactivations in cortical inhibitory regions after eating, which provides evidence of neural substrates associated with variable abnormal food motivation phenotypes in PWS and simple obesity.

When shown food logos, obese children showed significantly less brain activation than the healthy weight children in regions associated with cognitive control. This provides initial neuroimaging evidence that obese children may be more vulnerable to the effects of food advertising.

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Impulsive individuals make risky choices, motivated more by immediate reward than potential longterm negative consequences. We used event-related potentials to study the impact of reward and punishment sensitivity in impulsivity on risky decision-making in a two-card choice task in groups of 14 high and 14 low impulsive undergraduates formed by a median split on the Barratt Impulsiveness Scale score. The high impulsives had a larger P3 and the low impulsives a smaller P3 to the cards when making a low-risk choice suggesting that the high-risk option was the default choice of the high impulsives and the low-risk choice the default for the low impulsives. The low, but not the high impulsives had a larger error-related negativity following high-risk choice indicating that the low impulsives evaluated the risky choice as a poor decision. The results indicate that high impulsive individuals are biased towards immediate reward during option evaluation but are less sensitive to the negative consequences of their choices.