Cortical Grey Matter Mediates Increases in Model-Based Control and Learning from Positive Feedback from Adolescence to Adulthood.

Cognition and brain structure undergo significant maturation from adolescence into adulthood. Model-based (MB) control is known to increase across development, which is mediated by cognitive abilities. Here, we asked two questions unaddressed in previous developmental studies. First, what are the brain structural correlates of age-related increases in MB control? Second, how are age-related increases in MB control from adolescence to adulthood influenced by motivational context? A human developmental sample (n = 103; age, 12-50, male/female, 55:48) completed structural MRI and an established task to capture MB control. The task was modified with respect to outcome valence by including (1) reward and punishment blocks to manipulate the motivational context and (2) an additional choice test to assess learning from positive versus negative feedback. After replicating that an age-dependent increase in MB control is mediated by cognitive abilities, we demonstrate first-time evidence that gray matter density (GMD) in the parietal cortex mediates the increase of MB control with age. Although motivational context did not relate to age-related changes in MB control, learning from positive feedback improved with age. Meanwhile, negative feedback learning showed no age effects. We present a first report that an age-related increase in positive feedback learning was mediated by reduced GMD in the parietal, medial, and dorsolateral prefrontal cortex. Our findings indicate that brain maturation, putatively reflected in lower GMD, in distinct and partially overlapping brain regions could lead to a more efficient brain organization and might thus be a key developmental step toward age-related increases in planning and value-based choice.SIGNIFICANCE STATEMENT Changes in model-based decision-making are paralleled by extensive maturation in cognition and brain structure across development. Still, to date the neuroanatomical underpinnings of these changes remain unclear. Here, we demonstrate for the first time that parietal GMD mediates age-dependent increases in model-based control. Age-related increases in positive feedback learning were mediated by reduced GMD in the parietal, medial, and dorsolateral prefrontal cortex. A manipulation of motivational context did not have an impact on age-related changes in model-based control. These findings highlight that brain maturation in distinct and overlapping cortical regions constitutes a key developmental step toward improved value-based choices.

Working memory gating in obesity: Insights from a case-control fMRI study.

Computational models and neurophysiological data propose that a 'gating mechanism' coordinates distractor-resistant maintenance and flexible updating of working memory contents: While maintenance of information is mainly implemented in the prefrontal cortex, updating of information is signaled by phasic increases in dopamine in the striatum. Previous literature demonstrates structural and functional alterations in these brain areas, as well as differential dopamine transmission among individuals with obesity, suggesting potential impairments in these processes. To test this hypothesis, we conducted an observational case-control fMRI study, dividing participants into groups with and without obesity based on their BMI. We probed maintenance and updating of working memory contents using a modified delayed match to sample task and investigated the effects of SNPs related to the dopaminergic system. While the task elicited the anticipated brain responses, our findings revealed no evidence for group differences in these two processes, neither at the neural level nor behaviorally. However, depending on Taq1A genotype, which affects dopamine receptor density in the striatum, participants with obesity performed worse on the task. In conclusion, this study does not support the existence of overall obesity-related differences in working memory gating. Instead, we propose that potentially subtle alterations may manifest specifically in individuals with a 'vulnerable' genotype.

Self-reported intake of high-fat and high-sugar diet is not associated with cognitive stability and flexibility in healthy men.

Animal studies indicate that a high-fat/high-sugar diet (HFS) can change dopamine signal transmission in the brain, which could promote maladaptive behavior and decision-making. Such diet-induced changes may also explain observed alterations in the dopamine system in human obesity. Genetic variants that modulate dopamine transmission have been proposed to render some individuals more prone to potential effects of HFS. The objective of this study was to investigate the association of HFS with dopamine-dependent cognition in humans and how genetic variations might modulate this potential association. Using a questionnaire assessing the self-reported consumption of high-fat/high-sugar foods, we investigated the association with diet by recruiting healthy young men that fall into the lower or upper end of that questionnaire (low fat/sugar group: LFS, n = 45; high fat/sugar group: HFS, n = 41) and explored the interaction of fat and sugar consumption with COMT Val158Met and Taq1A genotype. During functional magnetic resonance imaging (fMRI) scanning, male participants performed a working memory (WM) task that probes distractor-resistance and updating of WM representations. Logistic and linear regression models revealed no significant difference in WM performance between the two diet groups, nor an interaction with COMT Val158Met or Taq1A genotype. Neural activation in task-related brain areas also did not differ between diet groups. Independent of diet group, higher BMI was associated with lower overall accuracy on the WM task. This cross-sectional study does not provide evidence for diet-related differences in WM stability and flexibility in men, nor for a predisposition of COMT Val158Met or Taq1A genotype to the hypothesized detrimental effects of an HFS diet. Previously reported associations of BMI with WM seem to be independent of HFS intake in our male study sample.

Brain response to food odors is not associated with body mass index and obesity-related metabolic health measures.

Smell perception plays a role in eating behavior and might be involved in the development of obesity. In fact, olfactory function is impaired in obesity and might depend on metabolic health factors. To date, the underlying neural mechanisms remain unclear. Here, we investigate neural processing of food-related odors in normal-weight, overweight and obese individuals. Fifty-three young and healthy participants (28.8 ± 4.4 years, 27 female; 24 normal-weight, 10 overweight, and 19 obese) were presented with high- (chocolate, potato chips) and low-caloric (orange, cucumber) food odors during a functional magnetic resonance imaging (fMRI). We also assessed olfactory identification ability, body mass index (BMI), body fat percentage, insulin resistance, and leptin levels. In brief, olfactory perception of food odors was linked to brain activity in the entorhinal and piriform cortex, and the insula, hippocampus, and amygdala. Insulin resistance was negatively related to olfactory identification. Additionally, perception of sweet versus savory odors was related to a higher brain activity in the right middle/superior frontal gyrus. Finally, we found no effect of obesity status, BMI, metabolic factors, or body fat percentage on neural responses to food odors. Overall, this suggests that food odor processing might depend on factors other than body weight status or associated markers of metabolic health.

Dopamine release, diffusion and uptake: A computational model for synaptic and volume transmission.

Computational modeling of dopamine transmission is challenged by complex underlying mechanisms. Here we present a new computational model that (I) simultaneously regards release, diffusion and uptake of dopamine, (II) considers multiple terminal release events and (III) comprises both synaptic and volume transmission by incorporating the geometry of the synaptic cleft. We were able to validate our model in that it simulates concentration values comparable to physiological values observed in empirical studies. Further, although synaptic dopamine diffuses into extra-synaptic space, our model reflects a very localized signal occurring on the synaptic level, i.e. synaptic dopamine release is negligibly recognized by neighboring synapses. Moreover, increasing evidence suggests that cognitive performance can be predicted by signal variability of neuroimaging data (e.g. BOLD). Signal variability in target areas of dopaminergic neurons (striatum, cortex) may arise from dopamine concentration variability. On that account we compared spatio-temporal variability in a simulation mimicking normal dopamine transmission in striatum to scenarios of enhanced dopamine release and dopamine uptake inhibition. We found different variability characteristics between the three settings, which may in part account for differences in empirical observations. From a clinical perspective, differences in striatal dopaminergic signaling contribute to differential learning and reward processing, with relevant implications for addictive- and compulsive-like behavior. Specifically, dopaminergic tone is assumed to impact on phasic dopamine and hence on the integration of reward-related signals. However, in humans DA tone is classically assessed using PET, which is an indirect measure of endogenous DA availability and suffers from temporal and spatial resolution issues. We discuss how this can lead to discrepancies with observations from other methods such as microdialysis and show how computational modeling can help to refine our understanding of DA transmission.

Hemispheric asymmetries in resting-state EEG and fMRI are related to approach and avoidance behaviour, but not to eating behaviour or BMI.

Much of our behaviour is driven by two motivational dimensions-approach and avoidance. These have been related to frontal hemispheric asymmetries in clinical and resting-state EEG studies: Approach was linked to higher activity of the left relative to the right hemisphere, while avoidance was related to the opposite pattern. Increased approach behaviour, specifically towards unhealthy foods, is also observed in obesity and has been linked to asymmetry in the framework of the right-brain hypothesis of obesity. Here, we aimed to replicate previous EEG findings of hemispheric asymmetries for self-reported approach/avoidance behaviour and to relate them to eating behaviour. Further, we assessed whether resting fMRI hemispheric asymmetries can be detected and whether they are related to approach/avoidance, eating behaviour and BMI. We analysed three samples: Sample 1 (n = 117) containing EEG and fMRI data from lean participants, and Samples 2 (n = 89) and 3 (n = 152) containing fMRI data from lean, overweight and obese participants. In Sample 1, approach behaviour in women was related to EEG, but not to fMRI hemispheric asymmetries. In Sample 2, approach/avoidance behaviours were related to fMRI hemispheric asymmetries. Finally, hemispheric asymmetries were not related to either BMI or eating behaviour in any of the samples. Our study partly replicates previous EEG findings regarding hemispheric asymmetries and indicates that this relationship could also be captured using fMRI. Our findings suggest that eating behaviour and obesity are likely to be mediated by mechanisms not directly relating to frontal asymmetries in neuronal activation quantified with EEG and fMRI.

Liking and left amygdala activity during food versus nonfood processing are modulated by emotional context.

Emotions can influence our eating behaviors. Facing an acute stressor or being in a positive mood are examples of situations that tend to modify appetite. However, the question of how the brain integrates these emotion-related changes in food processing remains elusive. Here, we designed an emotional priming fMRI task to test if amygdala activity during food pictures differs depending on the emotional context. Fifty-eight female participants completed a novel emotional priming task, in which emotional images of negative, neutral, or positive situations were followed by pictures of either foods or objects. After priming in each trial, participants rated how much they liked the shown foods or objects. We analyzed how brain activity during the contrast "foods > objects" changed according to the emotional context-in the whole brain and in the amygdala. We also examined the potential effect of adiposity (i.e., waist circumference). We observed a higher difference between liking scores for foods and objects after positive priming than after neutral priming. In the left amygdala, activity in the contrast "foods > objects" was higher after neutral priming relative to negative priming. Waist circumference was not significantly related to this emotional priming effect on food processing. Our results suggest that emotional context alters food and nonfood perception, both in terms of liking scores and with regard to engagement of the left amygdala. Moreover, our findings indicate that emotional context has an impact on the salience advantage of food, possibly affecting eating behavior.

Characterizing impulsivity and resting-state functional connectivity in normal-weight binge eaters.

OBJECTIVE: Binge eating is characterized by episodes of uncontrolled eating, within discrete periods of time. Although it is usually described in obese individuals or as a symptom of Binge Eating Disorder (BED), this behavior can also occur in the normal-weight (NW) population. An interesting premise suggests that impulsivity might contribute to the onset of binge eating and the progression toward weight gain. Drawing upon this evidence, here we explored impulsivity in NW individuals reporting binge-eating episodes through a functional connectivity approach. We hypothesized that, even in the absence of an eating disorder, NW binge eaters would be characterized by connectivity pattern changes in corticostriatal regions implicated in impulsivity, similarly to the results described in BED individuals. METHODS: A resting-state functional magnetic resonance imaging study tested 39 NW men and women, with and without binge eating (binge eaters, BE and non-BE). Brain functional connectivity was explored by means of graph theoretic centrality measures and traditional seed-based analysis; trait impulsivity was assessed with self-report questionnaires. RESULTS: The BE group was characterized by a higher degree of trait impulsivity. Brain functional connectivity measures revealed lower degree centrality within the right middle frontal gyrus, left insula/putamen and left temporoparietal regions and a lower functional connectivity between the right middle frontal gyrus and right insula in the BE group. DISCUSSION: The results support previous evidence on BED of altered functional connectivity and higher impulsivity at the roots of overeating behavior, but further extend this concept excluding any potential confounding effect exerted by the weight status.

Intermittent compared to continuous real-time fMRI neurofeedback boosts control over amygdala activation.

Real-time fMRI neurofeedback is a feasible tool to learn the volitional regulation of brain activity. So far, most studies provide continuous feedback information that is presented upon every volume acquisition. Although this maximizes the temporal resolution of feedback information, it may be accompanied by some disadvantages. Participants can be distracted from the regulation task due to (1) the intrinsic delay of the hemodynamic response and associated feedback and (2) limited cognitive resources available to simultaneously evaluate feedback information and stay engaged with the task. Here, we systematically investigate differences between groups presented with different variants of feedback (continuous vs. intermittent) and a control group receiving no feedback on their ability to regulate amygdala activity using positive memories and feelings. In contrast to the feedback groups, no learning effect was observed in the group without any feedback presentation. The group receiving intermittent feedback exhibited better amygdala regulation performance when compared with the group receiving continuous feedback. Behavioural measurements show that these effects were reflected in differences in task engagement. Overall, we not only demonstrate that the presentation of feedback is a prerequisite to learn volitional control of amygdala activity but also that intermittent feedback is superior to continuous feedback presentation.

Keeping track of promised rewards: Obesity predicts enhanced flexibility when learning from observation.

Goal-directed behaviour depends on successful association of environmental cues with reward or punishment. Obesity has been linked to diminished learning success in this domain. In contrast, here we demonstrate superior learning in obese participants independent of reward type. We tested association learning in 85 participants with a wide body-mass-index (BMI) range (lean to obese) in four probabilistic reversal-learning experiments. Experiments differed regarding learning mode (active and passive) and reward stimulus (pictures of snack food and money). Food and monetary rewards were adjusted regarding their motivational value in order to allow a direct comparison of related learning characteristics. Our results reveal enhanced associative learning in obese compared to normal-weight participants - reward-independently for expectancy updating and specifically for food-rewards for initial acquisition. When comparing the influence of continuous BMI in active and passive learning, food reward was associated with opposite effects of BMI on performance. Our data indicate generalized, weight-dependent differences in essential reward-learning, though particularly for food reward. We thereby argue that flexible updating of reward-related information may in fact be enhanced in people with obesity - and, thus, possibly promote unhealthy food choices in modern society.

Parasympathetic cardio-regulation during social interactions in individuals with obesity-The influence of negative body image.

Individuals with obesity in Western societies often face weight-related stigmatization and social exclusion. Recurrent exposure to prejudice and negative social feedback alters one's behavior in future social interactions. In this study, we aimed to investigate autonomic nervous system and affective responses to social interactions in individuals with obesity. Women and men with (n = 56) and without (n = 56) obesity participated in episodes of social inclusion and social exclusion using a virtual ball-tossing game. During the experiment, heart rate was measured and parasympathetic activity (overall high-frequency power and event-related cardiac slowing) was analyzed. Our results show that in novel social interactions, women with obesity, relative to the other groups, exhibited the strongest increase in parasympathetic activity. Furthermore, parasympathetic activity was related to a more negative body image in individuals with obesity, but not in lean individuals. Additionally, women with obesity reported a stronger decrease in mood after social exclusion than did the other participants. Our results demonstrate influences of objective and subjective bodily characteristics on parasympathetic cardio-regulation during social interactions. In particular, they show behavioral and physiological alterations during social interactions in women with obesity.

Effects of psychological eating behaviour domains on the association between socio-economic status and BMI.

OBJECTIVE: The current study investigates potential pathways from socio-economic status (SES) to BMI in the adult population, considering psychological domains of eating behaviour (restrained eating, uncontrolled eating, emotional eating) as potential mediators stratified for sex. DESIGN: Data were derived from the population-based cross-sectional LIFE-Adult-Study. Parallel-mediation models were conducted to obtain the total, direct and indirect effects of psychological eating behaviour domains on the association between SES and BMI for men and for women. SETTING: Leipzig, Germany. SUBJECTS: We studied 5935 participants aged 18 to 79 years. RESULTS: Uncontrolled eating mediated the association between SES and BMI in men only and restrained eating in both men and women. Emotional eating did not act as mediator in this relationship. The total effect of eating behaviour domains on the association between SES and BMI was estimated as ß=-0·03 (se 0·02; 95 % CI -0·062, -0·003) in men and ß=-0·18 (se 0·02; 95 % CI -0·217, -0·138) in women. CONCLUSIONS: Our findings do not indicate a strong overall mediation effect of the eating behaviour domains restrained eating, uncontrolled eating and emotional eating on the association between SES and BMI. Further research on other pathways of this association is strongly recommended. Importantly, our findings indicate that, independent from one's social position, focusing on psychological aspects in weight reduction might be a promising approach.

Cause or consequence? Investigating attention bias and self-regulation skills in children at risk for obesity.

Impaired self-regulation, especially in food-specific situations, has been linked to childhood obesity. These deficits may be acquired during the development of obesity rather than being a prerequisite thereof. The current study, hence, focused on an at-risk population versus controls. Normal-weight children of obese and normal-weight parents were tested regarding attentional flexibility, emotion regulation, and inhibitory control. A sample of 50 preschoolers of obese parents (n=25) or normal-weight parents (n=25) participated in this study. Through eye-tracking, attentional bias for food cues was measured during a visual probe task using food and toy images. Emotion regulation was assessed during a distress-evoking task, and inhibitory control was examined through a delay-of-gratification task. Both tasks are standardized and were conducted in non-food contexts. Results showed no significant group differences in overall attentional bias to food images over toy images. However, children of normal-weight parents showed a preference for toy images. Regarding emotion regulation, children in the risk group expressed significantly less overall emotional distress. In addition, less gaze aversion and bodily sadness could be observed in this group. No differences were found for inhibitory control. Findings suggest that general deficits in self-regulation are not yet present in normal-weight children at risk for obesity. Instead, they might develop as a by-product of unhealthy weight gain. Results indicate, however, that children of obese parents are less emotionally expressive compared with children of normal-weight parents. Furthermore, children of normal-weight parents appeared to be more interested in toy images than in food images.

Stopping at the sight of food - How gender and obesity impact on response inhibition.

Recent research indicates that reduced inhibitory control is associated with higher body mass index (BMI), higher food craving and increased food intake. However, experimental evidence for the relationship between response inhibition and weight status is inconsistent and to date has been investigated predominantly in women. In the current study, 56 participants (26 obese, 30 lean; 27 female, 29 male) performed a Food Picture Rating Task followed by a Stop Signal Task where pictures of palatable high or low caloric food or non-food items were presented prior to the Go signal. We further assessed participants' self-reported eating behavior and trait impulsivity as potential factors influencing response inhibition, in particular within the food context. Independent of BMI, women showed significantly higher liking for low caloric food items than men. This was accompanied by shorter Stop Signal Reaction Times (SSRT) after high compared to low caloric food pictures for women, and shorter SSRT in women compared to men for high caloric food. No influence of gender on SSRT was observable outside of the food context. While SSRTs did not differ between obese and lean participants across the three picture categories, we found a moderating effect of trait impulsivity on the relationship between BMI and SSRT, specifically in the high caloric food context. Higher BMI was predictive of longer SSRT only for participants with low to normal trait impulsivity, pointing at a complex interplay between response inhibition, general impulsivity and weight status. Our results support the notion that individuals with obesity do not suffer from diminished response inhibition capacity per se. Rather, the ability to withhold a response depends on context and social norms, and strongly interacts with factors like gender and trait impulsivity.

Comparison of variants of canonical correlation analysis and partial least squares for combined analysis of MRI and genetic data.

The standard analysis approach in neuroimaging genetics studies is the mass-univariate linear modeling (MULM) approach. From a statistical view, however, this approach is disadvantageous, as it is computationally intensive, cannot account for complex multivariate relationships, and has to be corrected for multiple testing. In contrast, multivariate methods offer the opportunity to include combined information from multiple variants to discover meaningful associations between genetic and brain imaging data. We assessed three multivariate techniques, partial least squares correlation (PLSC), sparse canonical correlation analysis (sparse CCA) and Bayesian inter-battery factor analysis (Bayesian IBFA), with respect to their ability to detect multivariate genotype-phenotype associations. Our goal was to systematically compare these three approaches with respect to their performance and to assess their suitability for high-dimensional and multi-collinearly dependent data as is the case in neuroimaging genetics studies. In a series of simulations using both linearly independent and multi-collinear data, we show that sparse CCA and PLSC are suitable even for very high-dimensional collinear imaging data sets. Among those two, the predictive power was higher for sparse CCA when voxel numbers were below 400 times sample size and candidate SNPs were considered. Accordingly, we recommend Sparse CCA for candidate phenotype, candidate SNP studies. When voxel numbers exceeded 500 times sample size, the predictive power was the highest for PLSC. Therefore, PLSC can be considered a promising technique for multivariate modeling of high-dimensional brain-SNP-associations. In contrast, Bayesian IBFA cannot be recommended, since additional post-processing steps were necessary to detect causal relations. To verify the applicability of sparse CCA and PLSC, we applied them to an experimental imaging genetics data set provided for us. Most importantly, application of both methods replicated the findings of this data set.

Genetic variants in AKR1B10 associate with human eating behavior.

BACKGROUND: The human Aldoketoreductase 1B10 gene (AKR1B10) encodes one of the enzymes belonging to the family of aldoketoreductases and may be involved in detoxification of nutrients during digestion. Further, AKR1B10 mRNA (messenger ribonucleic acid) expression was diminished in brain regions potentially involved in the regulation of eating behavior in rats which are more sensitive to cocaine and alcohol. We hypothesized that the human AKR1B10 gene may also play a role in the regulation of human eating behavior. RESULTS: We investigated the effects of 5 genetic variants of AKR1B10 on human eating behavior among 548 subjects from a German self-contained population, the Sorbs, and in 350 subjects from another independent German cohort. Among the Sorbs, we observed nominal associations with disinhibition at the 5' untranslated region (5' UTR) variant rs10232478 and the intragenic variants rs1834150 and rs782881 (all P ≤ 0.05). Further, we detected a relationship of rs1834150 and rs782881 with waist, smoking consumption (rs782881) and coffee consumption (rs1834150) (all P ≤ 0.05). Albeit non-significant, replication analyses revealed similar effect directions for disinhibition at rs1834150 (combined P = 0.0096). Moreover, in the replication cohort we found rs1834150 related to increased restraint scores with a similar direction as in the Sorbs (combined P = 0.0072). CONCLUSION: Our data suggest that genetic variants in the AKR1B10 locus may influence human eating behavior.

Slave to habit? Obesity is associated with decreased behavioural sensitivity to reward devaluation.

The motivational value of food is lower during satiety compared to fasting. Dynamic changes in motivational value promote food seeking or meal cessation. In obesity this mechanism might be compromised since obese subjects ingest energy beyond homeostatic needs. Thus, lower adaptation of eating behaviour with respect to changes in motivational value might cause food overconsumption in obesity. To test this hypothesis, we implemented a selective satiation procedure to investigate the relationship between obesity and the size of the behavioural devaluation effect in humans. Lean to obese men (mean age 25.9, range 19-30 years; mean BMI 29.1, range 19.2-45.1 kg/m(2)) were trained on a free operant paradigm and learned to associate cues with the possibility to win different food rewards by pressing a button. After the initial training phase, one of the rewards was devalued by consumption. Response rates for and wanting of the different rewards were measured pre and post devaluation. Behavioural sensitivity to reward devaluation, measured as the magnitude of difference between pre and post responses, was regressed against BMI. Results indicate that (1) higher BMI compared to lower BMI in men led to an attenuated behavioural adjustment to reward devaluation, and (2) the decrease in motivational value was associated with the decrease in response rate between pre and post. Change in explicitly reported motivational value, however, was not affected by BMI. Thus, we conclude that high BMI in men is associated with lower behavioural adaptation with respect to changes in motivational value of food, possibly resulting in automatic overeating patterns that are hard to control in daily life.

Age- and gender-specific norms for the German version of the Three-Factor Eating-Questionnaire (TFEQ).

The 'Fragebogen zum Essverhalten' (FEV) is the German version of the Three-factor-Eating-Questionnaire (TFEQ). This questionnaire covers three domains of eating behaviour ('cognitive restraint', 'disinhibition' and 'hunger') as well as common problems (e.g. craving for sweets). So far, there is a lack of normative data of the FEV especially for the middle-aged and older population. Aim of this study therefore was to provide age- and gender-specific norms of the FEV for the general population aged 40-79 years. We studied 3144 participants of the ongoing large community-based Leipzig Research Center for Civilization Diseases (LIFE) Health Care Study. We provided age- (four age groups: 40-49, 50-59, 60-69, and 70-79 years) and gender-specific percentile ranks and T-scores for the three domains of the FEV as well as age- and gender-specific frequencies of the common problems in eating behaviour. Females scored significantly higher than males in all three domains of the FEV (p < 0.001). Older individuals showed significantly higher mean scores than the younger ones in the domain of cognitive restraint, but lower mean scores in disinhibition and hunger (p < 0.001). 45.1% of the males and 69.9% of the females reported specific problems in eating. The main problem in both genders was craving for sweets (38.6%). Eating in response to stress was mostly reported in younger individuals. The present study offers current normative data for the FEV in the middle-aged and older general population that can be applied in clinical and non-clinical settings. Information on eating behaviour can be helpful in understanding body weight modulation, and thus, may help to improve interventive and preventive programmes for overweight, obesity, and eating disorders.

Response inhibition and its relation to multidimensional impulsivity.

Impulsivity is a multidimensional construct that has been suggested as a vulnerability factor for several psychiatric disorders, especially addiction disorders. Poor response inhibition may constitute one facet of impulsivity. Trait impulsivity can be assessed by self-report questionnaires such as the widely used Barratt Impulsiveness Scale (BIS-11). However, regarding the multidimensionality of impulsivity different concepts have been proposed, in particular the UPPS self-report questionnaire ('Urgency', 'Lack of Premeditation', 'Lack of Perseverance', 'Sensation Seeking') that is based on a factor analytic approach. The question as to which aspects of trait impulsivity map on individual differences of the behavioral and neural correlates of response inhibition so far remains unclear. In the present study, we investigated 52 healthy individuals that scored either very high or low on the BIS-11 and underwent a reward-modulated Stop-signal task during fMRI. Neither behavioral nor neural differences were observed with respect to high- and low-BIS groups. In contrast, UPPS subdomain Urgency best explained inter-individual variability in SSRT scores and was further negatively correlated to right IFG/aI activation in 'Stop>Go' trials - a key region for response inhibition. Successful response inhibition in rewarded compared to nonrewarded stop trials yielded ventral striatal (VS) activation which might represent a feedback signal. Interestingly, only participants with low Urgency scores were able to use this VS feedback signal for better response inhibition. Our findings indicate that the relationship of impulsivity and response inhibition has to be treated carefully. We propose Urgency as an important subdomain that might be linked to response inhibition as well as to the use of reward-based neural signals. Based on the present results, further studies examining the influence of impulsivity on psychiatric disorders should take into account Urgency as an important modulator of behavioral adaptation.

Brain imaging in the context of food perception and eating.

PURPOSE OF REVIEW: Eating behavior depends heavily on brain function. In recent years, brain imaging has proved to be a powerful tool to elucidate brain function and brain structure in the context of eating. In this review, we summarize recent findings in the fast growing body of literature in the field and provide an overview of technical aspects as well as the basic brain mechanisms identified with imaging. Furthermore, we highlight findings linking neural processing of eating-related stimuli with obesity. RECENT FINDINGS: The consumption of food is based on a complex interplay between homeostatic and hedonic mechanisms. Several hormones influence brain activity to regulate food intake and interact with the brain's reward circuitry, which is partly mediated by dopamine signaling. Additionally, it was shown that food stimuli trigger cognitive control mechanisms that incorporate internal goals into food choice. The brain mechanisms observed in this context are strongly influenced by genetic factors, sex and personality traits. SUMMARY: Overall, a complex picture arises from brain-imaging findings, because a multitude of factors influence human food choice. Although several key mechanisms have been identified, there is no comprehensive model that is able to explain the behavioral observations to date. Especially a careful characterization of patients according to genotypes and phenotypes could help to better understand the current and future findings in neuroimaging studies.