Food craving, food choice and consumption: The role of impulsivity and sham-controlled tDCS stimulation of the right dlPFC

Identifying and understanding mechanisms in an inhibitory control training in patients with binge-eating-disorder - an exploratory analysis

Cognitive processes play a central role in the development, maintenance, and remission of mental disorders, like Binge Eating Disorder (BED). Cognitive trainings aim to alter those cognitive processes to achieve amelioration of psychopathology. Regardless, little is known about the underlying mechanisms that can explain effective treatment in BED. Therefore, we analyzed findings from a clinical randomized-controlled trial (RCT) (Giel, Schag et al., 2023) which used an individualized computer-based inhibitory control training programme enhanced by transcranial direct current stimulation (tDCS). At the beginning of the treatment, for each person the 20 highest-rated food stimuli concerning valence, appetite, liking and wanting out of 40 high-calorie food stimuli were selected. In total, 41 patients were included in the study, 39 of those completed the training. Overall, we identified a devaluation effect for food stimuli used in the training programme: after completion of the six training sessions a significant reduction of valence, appetite, liking, and wanting of food stimuli being used in the training were observed whereas this effect was absent of food stimuli not being used in the training programme. However, the individual devaluation effect did not predict the degree of binge eating frequency reduction. As predictor variables for effective treatment, we found specific dimensions of food valence at the baseline- or follow-up-measurement to be predictive for the binge eating frequency reduction. Lastly, we found a reduction of eating concerns as well as an increase in general well-being as a predictor for binge eating frequency reduction which might indicate a potential mechanism of the inhibitory control training. Future studies might focus additionally on emotion, affect and affect regulation to complete the multifaceted clinical picture of BED to target its underlying processes to achieve effective treatment with cognitive trainings.

Repeated net-tDCS of the hypothalamus appetite-control network enhances inhibitory control and decreases sweet food intake in persons with overweight or obesity

BACKGROUND

Reduced inhibitory control is associated with obesity and neuroimaging studies indicate that diminished prefrontal cortex activity influence eating behavior and metabolism. The hypothalamus regulates energy homeostasis and is functionally connected to cortical and subcortical regions especially the frontal areas.

OBJECTIVES

We tested network-targeted transcranial direct current stimulation (net-tDCS) to influence the excitability of brain regions involved in appetite control.

METHODS

In a randomized, double-blind parallel group design, 44 adults with overweight or obesity (BMI 30.6 kg/m2, 52.3 % female) received active (anodal or cathodal) or sham 12-channel net-tDCS on the hypothalamus appetite-control network for 25 min on three consecutive days while performing a Stop-Signal-Task to measure response inhibition. Before and after stimulation, state questionnaires assessed changes in desire to eat and food craving. Directly after stimulation, participants received a breakfast buffet to evaluate ad-libitum food intake. An oral glucose tolerance test was conducted at follow-up. Resting-state functional MRI was obtained at baseline and follow-up.

RESULTS

The Stop-Signal Reaction Time (SSRT) was shorter in both active groups versus sham, indicating improved response inhibition. Additionally, a stronger increase in hypothalamic functional connectivity was associated with shorter SSRT. Caloric intake of sweet food was lower in the anodal group versus sham, but no main effects between groups were observed on total and macronutrient intake, food craving ratings and desire to eat. At follow-up, no differences were observed between groups on peripheral metabolism.

CONCLUSION

Our study suggests that modulating hypothalamic functional network connectivity patterns via net-tDCS may improve food choice and inhibitory control.

Effective non-invasive brain stimulation over dorsolateral prefrontal cortex for modulation of food craving and consumption: A systematic and meta-analytic review

In recent decades, non-invasive brain stimulation (NIBS) has gained attention as a potential tool for promoting dietary regulation by modulating activity in the dorsolateral prefrontal cortex (dlPFC). However, the findings from individual experimental studies and meta-analyses have been inconsistent. To address this, we conducted a meta-analytic and systematic review of past studies focusing on neuromodulation of the dlPFC. Our research included 13 studies using repetitive transcranial magnetic stimulation (rTMS; 16 samples, 506 participants) and 29 transcranial direct current stimulation (tDCS; 31 samples, 1004 participants). By adjusting the pre-post correlation, we detected small-to-moderate effect sizes of NIBS on food craving (rTMS: Hedge's g = -0.57; tDCS: Hedge's g = -0.26) and food consumption (rTMS: Hedge's g = -0.51; tDCS: Hedge's g = -0.17). Additionally, we observed that the efficacy of NIBS was influenced by various moderators, including stimulation parameters, research protocols, and participant characteristics. Notably, both rTMS and tDCS appeared to enhance dlPFC function in dietary regulation for people with eating disorders or obesity. Furthermore, these effects were more pronounced with multi-session stimulation compared to single-session stimulation. Finally, based on the existing literature, we discuss the role of the dlPFC in the appetitive reward processing pathway and provide suggestions for future research directions.

The use of combined cognitive training and non-invasive brain stimulation to modulate impulsivity in adult populations: a systematic review and meta-analysis of existing studies

Introduction

Impulsivity, a tendency to act rashly and without forethought, is a core feature of many mental disorders that has been implicated in suicidality and offending behaviours. While research supports the use of non-invasive brain stimulation (NIBS) techniques, such as transcranial direct current stimulation (tDCS), to modulate brain functions, no studies specifically reviewed the use of combined cognitive training and NIBS to modulate impulsivity.

Methods

We aimed to conduct a systematic review and meta-analysis to synthesise the literature on the use of combined cognitive training and NIBS to modulate impulsivity and its subdomains (motor, delay discounting, reflection). We searched Scopus, PsychInfo, Medline, and Cinahl electronic databases, dissertations database, and Google scholar up to September 2024.

Results

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, four randomised controlled studies involving the use of combined cognitive training and tDCS in 127 subjects were included in the study. These studies included subjects with substance use disorders, obesity, and Parkinson's disease. Meta-analysis showed that combined cognitive training and tDCS had no statistically significant effects on motor impulsivity as measured using reaction times on the Stop Signal Task and Go/No Go tasks. One study that measured impulsiveness scores on a delay discounting task also showed no significant results. No studies measured reflection or cognitive impulsivity.

Discussion

There is a dearth of literature on the use of combined cognitive training and NIBS for impulsivity. This in conjunction of clinical heterogeneity across studies makes it difficult to draw definitive conclusions about the neuromodulation of impulsivity and its subdomains using combined cognitive training and NIBS. The findings of this study highlight the need to conduct more studies in the field.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD 42024511576.

The dorsomedial prefrontal cortex promotes self-control by inhibiting the egocentric perspective

The dorsomedial prefrontal cortex (dmPFC) plays a crucial role in social cognitive functions, including perspective-taking. Although perspective-taking has been linked to self-control, the mechanism by which the dmPFC might facilitate self-control remains unclear. Using the multimodal neuroimaging dataset from the Human Connectome Project (Study 1, N =978 adults), we established a reliable association between the dmPFC and self-control, as measured by discounting rate-the tendency to prefer smaller, immediate rewards over larger, delayed ones. Experiments (Study 2, N = 36 adults) involving high-definition transcranial direct current stimulation showed that anodal stimulation of the dmPFC reduces the discounting of delayed rewards and decreases the congruency effect in egocentric but not allocentric perspective in the visual perspective-taking tasks. These findings suggest that the dmPFC promotes self-control by inhibiting the egocentric perspective, offering new insights into the neural underpinnings of self-control and perspective-taking, and opening new avenues for interventions targeting disorders characterized by impaired self-regulation.

Impact of multiple-session home-based transcranial direct current stimulation (M-HB-tDCS) on eating behavior in fibromyalgia: A factorial randomized clinical trial

BACKGROUND

Multiple-session home-based self-applied transcranial direct current stimulation (M-HB-self-applied-tDCS) has previously been found to effectively reduce chronic pain and enhance cognitive function. However, the effectiveness of this method for disordered eating behavior still needs to be studied.

OBJECTIVE

This study aimed to assess whether 20 sessions of M-HB-self-applied-tDCS, administered over four weeks to either the left dorsolateral prefrontal cortex (L-DLPFC) or primary motor cortex (M1), could improve various aspects of eating behavior, anthropometric measures, and adherence.

METHODS

We randomly assigned 102 fibromyalgia patients between the ages of 30 and 65 to one of four tDCS groups: L-DLPFC (anodal-(a)-tDCS, n = 34; sham-(s)-tDCS, n = 17) or M1 (a-tDCS, n = 34; s-tDCS, n = 17). Patients self-administered 20-min tDCS sessions daily with 2 mA under remote supervision following in-person training.

RESULTS

Generalized linear models revealed significant effects of M-HB-self-applied-tDCS compared to s-tDCS on uncontrolled eating (UE) (Wald χ2 = 5.62; df = 1; P = 0.018; effect size, ES = 0.55), and food craving (Wald χ2 = 5.62; df = 1; P = 0.018; ES = 0.57). Regarding fibromyalgia symptoms, we found a differentiated impact of a-tDCS on M1 compared to DLPFC in reducing food cravings. Additionally, M-HB-a-tDCS significantly reduced emotional eating and waist size. In contrast, M1 stimulation was more effective in improving fibromyalgia symptoms. The global adherence rate was high, at 88.94%.

CONCLUSION

These findings demonstrate that M-HB-self-applied-tDCS is a suitable approach for reducing uncontrolled and emotional eating, with greater efficacy in L-DLPFC. Furthermore, these results revealed the influence of fibromyalgia symptoms on M-HB-self-applied-tDCS's, with M1 being particularly effective in mitigating food cravings and reducing fibromyalgia symptoms.

Efficacy of Transcranial Direct Current Stimulation for Controlling of Food Craving in Subjects With Overweight or Obesity: A Pilot Study

OBJECTIVE

We aim to explore the effects of transcranial direct current stimulation (tDCS) on food craving improvement and changes in brain function associated with craving by conducting a total of 10 sessions of tDCS over a period of 2 weeks on overweight and obese subjects.

METHODS

A total of 15 patients who were overweight or obese (body mass index [BMI] ≥23 kg/m2) were included. Weight, BMI, neuropsychological variables, and food craving-related variables were assessed. We measured absolute and relative power in 19 channels and analyzed quantitative electroencephalography (qEEG) according to the following frequency ranges: delta (1-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), beta (12-25 Hz), high beta (25-30 Hz), and gamma (30-80 Hz).

RESULTS

After the application of tDCS, there was no significant reduction observed in weight and BMI. However, all measures related to food and eating showed a decrease in the intensity of cravings, and there was also a significant reduction in depression, anxiety, and perceived stress. In qEEG analysis, an increase in theta waves was observed in the left frontal area (F7 and F3), an increase in alpha waves in the right parietal area (P4), and a decrease in beta waves in the frontal area (FP2) and occipital area (O1).

CONCLUSION

This study confirmed the beneficial effects of tDCS on food craving regulation in overweight or obese individuals and observed improved scores in psychological factors such as depression and anxiety. Furthermore, neurophysiological changes related to food craving were observed using qEEG.

The role of emotion in eating behavior and decisions

The present paper aims to provide the latest perspectives and future directions on the association between emotions and eating behavior. We discussed individual differences in the impact of negative emotions on eating, emotional eating as disinhibited eating decisions with heightened reward values of and sensitivity to palatable foods in response to negative emotions and social isolation, in addition to emotional eating as maladaptive coping strategies under negative emotion and stress, hedonic (pleasure-oriented) eating decisions mediated by the brain reward system, and self-controlled (health-oriented) eating decisions mediated by the brain control system. Perspectives on future directions were addressed, including the development of early eating phenotypes in infancy, shared neural mechanisms mediated by the ventromedial prefrontal cortex and the dorsolateral prefrontal cortex in emotion and eating decision regulation, possible roles of interoception incorporating hunger and satiety signals, gut microbiome, the insula and the orbitofrontal cortex, and emotional processing capacities in hedonic eating and weight gain.

No effect of prefrontal transcranial direct current stimulation (tDCS) on food craving, food reward and subjective appetite in females displaying mild-to-moderate binge-type behaviour

Previous work suggests there may be an effect of transcranial direct current stimulation (tDCS) on appetite control in people at risk of overconsumption, however findings are inconsistent. This study aimed to further understand the potential eating behaviour trait-dependent effect of tDCS, specifically in those with binge-type behaviour. Seventeen females (23 ± 7 years, 25.4 ± 3.8 kg m-2) with mild-to-moderate binge eating behaviour completed two sessions of double-blind, randomised and counterbalanced anodal and sham tDCS applied over the right dorsolateral prefrontal cortex at 2.0 mA for 20 min. Subjective appetite visual analogue scales (VAS), the Food Craving Questionnaire-State (FCQ-S), and Leeds Food Preference Questionnaire (LFPQ) were completed pre- and post-tDCS. Participants then consumed a fixed-energy meal, followed by the VAS, FCQ-S and LFPQ. No difference between pre- and post-tDCS scores were found across fullness (p = 0.275, BF10 = 0.040), prospective consumption (p = 0.127, BF10 = 0.063), desire to eat (p = 0.247, BF10 = 0.054) or FCQ-S measures (p = 0.918, BF10 = 0.040) when comparing active and sham protocols. Only explicit liking and wanting for high-fat sweet foods were significantly different between conditions, with increased scores following active tDCS. When controlling for baseline hunger, the significant differences were removed (p = 0.138 to 0.161, BF10 = 0.810 to 1.074). The present data does not support the eating behaviour trait dependency of tDCS in a specific cohort of female participants with mild-to-moderate binge eating scores, and results align with those from individuals with healthy trait scores. This suggests participants with sub-clinical binge eating behaviour do not respond to tDCS. Future work should further explore effects in clinical and sub-clinical populations displaying susceptibility to overconsumption and weight gain.

Metabolic hormone action in the VTA: Reward-directed behavior and mechanistic insights

Dysfunctional signaling in midbrain reward circuits perpetuates diseases characterized by compulsive overconsumption of rewarding substances such as substance abuse, binge eating disorder, and obesity. Ventral tegmental area (VTA) dopaminergic activity serves as an index for how rewarding stimuli are perceived and triggers behaviors necessary to obtain future rewards. The evolutionary linking of reward with seeking and consuming palatable foods ensured an organism's survival, and hormone systems that regulate appetite concomitantly developed to regulate motivated behaviors. Today, these same mechanisms serve to regulate reward-directed behavior around food, drugs, alcohol, and social interactions. Understanding how hormonal regulation of VTA dopaminergic output alters motivated behaviors is essential to leveraging therapeutics that target these hormone systems to treat addiction and disordered eating. This review will outline our current understanding of the mechanisms underlying VTA action of the metabolic hormones ghrelin, glucagon-like peptide-1, amylin, leptin, and insulin to regulate behavior around food and drugs of abuse, highlighting commonalities and differences in how these five hormones ultimately modulate VTA dopamine signaling.

Neurobiological regulation of eating behavior: Evidence based on non-invasive brain stimulation

The prefrontal cortex is appreciated as a key neurobiological player in human eating behavior. A special focus is herein dedicated to the dorsolateral prefrontal cortex (DLPFC), which is critically involved in executive function such as cognitive control over eating. Persons with obesity display hypoactivity in this brain area, which is linked to overconsumption and food craving. Contrary to that, higher activity in the DLPFC is associated with successful weight-loss and weight-maintenance. Transcranial direct current stimulation (tDCS) is a non-invasive neurostimulation tool used to enhance self-control and inhibitory control. The number of studies using tDCS to influence eating behavior rapidly increased in the last years. However, the effectiveness of tDCS is still unclear, as studies show mixed results and individual differences were shown to be an important factor in the effectiveness of non-invasive brain stimulation. Here, we describe the current state of research of human studies using tDCS to influence food intake, food craving, subjective feeling of hunger and body weight. Excitatory stimulation of the right DLPFC seems most promising to reduce food cravings to highly palatable food, while other studies provide evidence that stimulating the left DLPFC shows promising effects on weight loss and weight maintenance, especially in multisession approaches. Overall, the reported findings are heterogeneous pointing to large interindividual differences in tDCS responsiveness.

Effective Transcranial Direct Current Stimulation Parameters for the Modulation of Eating Behavior: A Systematic Literature Review and Meta-Analysis

OBJECTIVE

This study aimed to consider the effect of differing transcranial direct current stimulation (tDCS) parameters on eating-related measures and how issues with experimental design (e.g., inadequate blinding) or parameters variation may drive equivocal effects.

METHODS

Literature searches were conducted across MEDLINE, PsycINFO, Scopus, and Science Direct. Studies using conventional sham-controlled tDCS to modify eating-related measures in adult human participants were included. A total of 1135 articles were identified and screened by two independent authors. Study quality was assessed using the Risk of Bias tool. Random-effects meta-analyses were performed, with subgroup analyses to determine differences between parameter sets.

RESULTS

We identified 28 eligible studies; 7 showed low risk of bias, with the remaining studies showing bias arising from issues implementing or reporting blinding protocols. Large variation in applied parameters was found, including montage, current intensity and density, participant and researcher blinding, and the use of online or offline tasks. The application of differing parameters seemed to alter the effects of tDCS on eating-related measures, particularly for current density ( g = -0.25 to 0.31), and when comparing single-session ( g = -0.08 to 0.01) versus multisession protocols ( g = -0.34 to -0.29). Some parameters result in null effects.

CONCLUSIONS

The absence of tDCS-mediated change in eating-related measures may be driven by variation in applied parameters. Consistent application of parameters that seem to be effective for modulating eating behavior is important for identifying the potential impact of tDCS. Using the findings of this review, we propose a series of parameters that researchers should apply in their work.

Neural mechanisms of the mood effects on third‐party responses to injustice after unfair experiences

Behavioral decision theory argues that humans can adjust their third‐party responses (e.g., punishment and compensation) to injustice by integrating unfair experiences. Typically, the mood plays an important role in such a decision‐making process. However, the underlying neurocognitive bases remain largely unclear. We first employ a modified third‐party justice game in which an allocator split an amount of money between oneself and a receiver. The participants can reapportion the money as observers by choosing from the following three costly options: compensate the receiver, accept the current allocation, or punish the allocator. Then, a second‐party pseudo interaction is conducted where participants receive more (i.e., advantageous unfair experience) or less (i.e., disadvantageous unfair experience) than others. Finally, participants perform the third‐party justice game again after unfair experiences. Here, we use functional near‐infrared spectroscopy (fNIRS) to measure participants' brain activities during third‐party responses to injustice. We find participants compensate more to the receiver after advantageous unfair experience, which involved enhanced positive emotion, weakened sense of unfairness, and is linked with increased activity in the right dorsolateral prefrontal cortex (rDLPFC). In contrast, participants punish more on the allocator after disadvantageous unfair experience, which might primarily stem from their negative emotional responses, strong sense of unfairness, and is associated with significantly decreased activity in the rDLPFC. Our results suggest that third‐party compensation and punishment involved differential psychological and neural bases. Our findings highlight the crucial roles of second‐party unfair experiences and the corresponding mood responses in third‐party responses to unfairness, and unravel the intermediate neural architecture.

Modulating eating behavior with transcranial direct current stimulation (tDCS): A systematic literature review on the impact of eating behavior traits

Transcranial direct current stimulation (tDCS) is becoming an increasingly popular technique for altering eating behaviors. Recent research suggests a possible eating behavior trait-dependent effect of tDCS. However, studies recruit participant populations with heterogeneous trait characteristics, including "healthy" individuals who do not present with eating behavior traits suggesting susceptibility to overconsumption. The present review considers the effects of tDCS across eating-related measures and explores whether a trait-dependent effect is evident across the literature. A literature search identified 28 articles using sham-controlled tDCS to modify eating-related measures. Random effects meta-analyses were performed, with subgroup analyses to identify differences between "healthy" and trait groups. Trivial overall effects (g = -0.12 to 0.09) of active versus sham tDCS were found. Subgroup analyses showed a more consistent effect for trait groups, with small and moderate effect size (g = -1.03 to 0.60), suggesting tDCS is dependent on participants' eating behavior traits. Larger effect sizes were found for those displaying traits associated with study outcomes (e.g., heightened food cravings). "Healthy" individuals appear to be unresponsive to stimulation. Based on this meta data, future work should recruit those with eating behavior trait susceptibilities to overconsumption, focusing on those who present with traits associated with the outcome of interest.

How Impulsiveness Influences Obesity: The Mediating Effect of Resting-State Brain Activity in the dlPFC

Impulsiveness is a stable personal characteristic that contributes to obesity and may interact with it. Specifically, obesity is caused by unrestrained impulse eating that is not consciously controlled and leads to a hormonal imbalance that also can impair impulse control. However, the mechanism of this relationship is unclear. In our study, 35 obese individuals (body mass index, BMI > 28) were recruited and matched with 31 healthy controls (BMI < 24) in age and education level. All the participants underwent a resting-state fMRI and completed the Barratt Impulsiveness Scale-11. The results showed that patients with obesity had a significantly lower fractional amplitude of low-frequency fluctuations (fALFF) in the bilateral dorsolateral prefrontal cortex (dlPFC) and higher fALFF in the left fusiform cortex. In addition, non-planning impulsiveness was positively correlated with BMI. Importantly, we found that the right dlPFC completely mediated the relationship between non-planning impulsiveness and BMI. Our findings suggest that impulsivity is statistically more likely to precede obesity than to precede impulsivity and contributes to obesity by downregulating spontaneous activity in the dlPFC. This suggests that the dlPFC, which is associated with executive control, may be able a potential target for treating obesity.

Heritable variation in locomotion, reward sensitivity and impulsive behaviors in a genetically diverse inbred mouse panel

Drugs of abuse, including alcohol and stimulants like cocaine, produce effects that are subject to individual variability, and genetic variation accounts for at least a portion of those differences. Notably, research in both animal models and human subjects point toward reward sensitivity and impulsivity as being trait characteristics that predict relatively greater positive subjective responses to stimulant drugs. Here we describe use of the eight collaborative cross (CC) founder strains and 38 (reversal learning) or 10 (all other tests) CC strains to examine the heritability of reward sensitivity and impulsivity traits, as well as genetic correlations between these measures and existing addiction-related phenotypes. Strains were all tested for activity in an open field and reward sensitivity (intake of chocolate BOOST®). Mice were then divided into two counterbalanced groups and underwent reversal learning (impulsive action and waiting impulsivity) or delay discounting (impulsive choice). CC and founder mice show significant heritability for impulsive action, impulsive choice, waiting impulsivity, locomotor activity, and reward sensitivity, with each impulsive phenotype determined to be non-correlating, independent traits. This research was conducted within the broader, inter-laboratory effort of the Center for Systems Neurogenetics of Addiction (CSNA) to characterize CC and DO mice for multiple, cocaine abuse related traits. These data will facilitate the discovery of genetic correlations between predictive traits, which will then guide discovery of genes and genetic variants that contribute to addictive behaviors.

Can sweet food-specific inhibitory control training via a mobile application improve eating behavior in children with obesity?

OBJECTIVES

Consumption of excess sugar, a common energy-dense nutrient-poor food, is a risk factor for obesity in school-aged children. Food-specific inhibition training, where responses to palatable food stimuli, such as sweet foods, are consistently and repeatedly inhibited, reduces sweet food intake in adults. However, no studies have yet examined the effectiveness of inhibitory control training specifically targeting sweet foods among children with high sugar cravings. We examined whether sweet food-specific inhibitory control training (SF-ICT), administered via a mobile app, reduced choice and consumption of sweet foods, and weight in a sample of children aged 7-11 with overweight or obesity and who had high sugar cravings (N = 46).

DESIGN

This study was designed as a 2 × 3 between-within design.

METHODS

Participants were randomly allocated to a single-blind design with two conditions: they either received 7 sessions of active or control go/no-go training in which either sweet foods or non-food cues were paired with no-go signals. Participants' weight, sweet food choice, and consumption were measured pre and post-training, and at three-month follow-up.

RESULTS

The results revealed that participants in the active group showed a significant reduction in sweet food choice and intake from pre to post-training relative to the control group. The effects of the training on reducing sweet food intake persisted over the 3-month follow-up No significant changes in weight loss were observed.

CONCLUSIONS

These results provide preliminary evidence that sweet food-specific inhibitory control training (SF-ICT) via a mobile app is effective in modifying eating behavior among children with excessive consumption of sugary foods. Further research is required to clarify under what conditions the benefits of training would expand to weight loss.

A systematic review on neuromodulation therapies for reducing body weight in patients with obesity

The global prevalence of obesity increases yearly along with a rising demand for efficacious, safe, and accessible treatments. Neuromodulation interventions (i.e., deep brain stimulation [DBS], transcranial magnetic stimulation [TMS], transcranial direct current stimulation [tDCS], percutaneous neurostimulation [PENS], vagus nerve stimulation [VNS], and gastric electrical stimulation [GES]) have been proposed as novel therapies. This systematic review sought to examine the safety and efficacy of neuromodulation therapies in reducing body weight in patients with obesity. Using PRISMA guidelines, we performed a systematic review for studies on neuromodulation for the treatment of obesity, resulting in 60 trials included (7 DBS, 5 TMS, 7 tDCS, 17 PENS and VNS, and 24 GES; a total of 3,042 participants). While promising results have been reported in open label studies, double-blinded randomized clinical trials often did not reach their primary endpoints, with no technique inducing a striking reduction in body weight. Bearing in mind the complexity and multifactorial nature of obesity, it is possible that a single treatment may not be enough for patients to lose or maintain the weight lost at long term.

Neuroanatomical Correlates of Binge-Eating Behavior: At the Roots of Unstoppable Eating

Binge-eating refers to episodes of uncontrolled eating accompanied by a perceived loss of control, which can be common in the general population. Given the profound negative consequences of persistent binge-eating such as weight and eating disorders, it is vital to determine what makes someone more vulnerable than others to engage in such a conduct. A total of 42 normal-weight individuals (21 with binge-eating episodes and 21 without binge-eating episodes) underwent a structural magnetic resonance imaging measurement and Voxel-based morphometry (VBM) was used to assess between-group differences in terms of gray matter volume (GMV), together with self-report impulsivity and binge-eating measures. The results showed binge-eating individuals as characterized by higher trait impulsivity and greater regional GMV in the left middle frontal gyrus: however, the GMV in this region appeared to be positively correlated only with measures of binge-eating but not with trait impulsivity measures. These findings provide novel insights on the neurobiological roots of BE in normal-weight individuals and highlight how this behavior can be associated with brain morphometric changes within prefrontal regions also in a non-clinical population. Overall, this study provides a further characterization of the neural correlates of binge-eating and novel insights into the treatment of its more severe pathological forms.

The effect of transcranial direct current stimulation (tDCS) on food craving, reward and appetite in a healthy population

The ability to control hedonic appetite is associated with executive functioning, originating in the prefrontal cortex (PFC). These rewarding components of food can override homeostatic mechanisms, potentiating obesogenic behaviours. Indeed, those susceptible to overconsumption appear to have PFC hypo-activation. Transcranial direct current stimulation (tDCS) over the dorsolateral PFC (DLPFC) has been shown to reduce food craving and consumption, potentially via attenuating this reward response. We examined the effects of stimulation on food reward and craving using a healthy-weight cohort. This study is amongst the first to explore the effects of tDCS on explicit and implicit components of reward for different food categories. Twenty-one healthy-weight participants (24 ± 7 years, 22.8 ± 2.3 kg m^-2) completed two sessions involving double-blind, randomised and counterbalanced anodal or sham tDCS over the right DLPFC, at 2 mA for 20 min. Food craving (Food Craving Questionnaire-State), reward (Leeds Food Preference Questionnaire), and subjective appetite (100 mm visual analogue scales) were measured pre- and post-tDCS. Eating behaviour trait susceptibility was assessed using the Three Factor Eating Questionnaire-Short Form, Control of Eating Questionnaire, and Food Craving Questionnaire-Trait-reduced. Stimulation did not alter food craving, reward or appetite in healthy-weight participants who displayed low susceptibility to overconsumption, with low trait craving, good craving control, and low uncontrolled eating and emotional eating behaviour. Implicit and explicit reward were reliable measures of hedonic appetite, suggesting these are robust targets for future tDCS research. These findings suggest that applying tDCS over the DLPFC does not change food reward response in individuals not at risk for overconsumption, and future work should focus on those at risk of overconsumption who may be more responsive to the effects of tDCS on hedonic appetite.

A Meta-Analysis of Transcranial Direct Current Stimulation on Substance and Food Craving: What Effect Do Modulators Have?

Substance addiction and food addiction are significant social problems worldwide. In previous studies of substance addiction, transcranial direct current stimulation (tDCS) has been used to influence craving of substance or food. However, the reported effects are not always consistent due to inconsistent experimental settings. The way modulators influence the effect of tDCS on substance addiction is worth exploring. This meta-analysis was conducted to estimate the effect size of tDCS on substance and food craving and to investigate the influence of potential modulators. We systemically identified and reviewed studies on substance/food craving using tDCS that were published between January 2008 to January 2020. A total of 32 eligible studies were identified. Hedges' g was computed as an indicator of the effect of tDCS and some potential moderators (substance type, stimulation sites, current intensities, number of sessions, duration of stimulation, and study design) were examined using subgroup analysis. Random effects analysis revealed a total medium effect size [Hedges' g = 0.536, 95% confidence interval (CI): 0.389-0.683, after adjusting Hedges' g = 0.416, 95% CI: 0.262-0.570] preferring active over sham stimulation to reduce craving. A significant difference was observed between the number of sessions (repeated stimulation was better than single stimulation). The duration of stimulation may have a positive influence on the effects of tDCS. No other significant differences were found in other subgroups analysis. In conclusion, our results provided evidence that tDCS can be an effective way to reduce craving of substance or food, and longer multiple stimulus durations in all can more effectively reduce craving; however, the influences of modulators still need be to be examined in depth in future.

Effect of Impulsivity Traits on Food Choice within a Nudging Intervention

Food choices are often driven by impulsive tendencies rather than rational consideration. Some individuals may find it more difficult resisting impulses related to unhealthy food choices, and low self-control and high impulsivity have been suggested to be linked to these behaviors. Recent shifts have been made towards developing strategies that target automatic processes of decision-making and focus on adjusting the environment, referred to as nudging interventions. Therefore, the purpose of this study was to investigate the effect of impulsivity traits on food choices within a nudging intervention (increased perceived variety). A total of 83 adults participated in an experimental study consisting of a self-service intelligent buffet. Impulsivity traits were measured using the UPPS-P impulsivity scale. General linear models were fitted to evaluate the effect of the five impulsivity traits on the difference of salad consumption (g) between the control and intervention situations. Results showed that impulsivity does not affect food choices in this nudging situation, suggesting that nudging works independently of the participant's impulsivity score. Results also showed a significantly higher consumption of salad in the nudging versus the control setting (17.6 g, p < 0.05), suggesting that nudging interventions can be effective in significantly increasing total vegetable consumption across the whole impulsivity scale.

Can transcranial direct current stimulation (tDCS) improve impulsivity in healthy and psychiatric adult populations? A systematic review

Impulsivity is a multidimensional phenomenon that remains hard to define. It compounds the core pathological construct of many neuropsychiatric illnesses, and despite its close relation to suicide risk, it currently has no specific treatment. Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique whose application results in cognitive function improvement, both in healthy and psychiatric populations. Following PRISMA recommendations, a systematic review of the literature concerning tDCS's effects on impulsive behaviour was performed using the PubMed database. The research was based on the combination of the keyword 'tDCS' with 'impulsivity', 'response inhibition', 'risk-taking', 'planning', 'delay discounting' or 'craving'. The initial search yielded 309 articles, 92 of which were included. Seventy-four papers demonstrated improvement in task performance related to impulsivity in both healthy and clinical adult populations. However, results were often inconsistent. The conditions associated with improvement, such as tDCS parameters and other aspects that may influence tDCS's outcomes, are discussed. The overall effects of tDCS on impulsivity are promising. Yet further research is required to develop a more comprehensive understanding of impulsivity, allowing for a more accurate assessment of its behavioural outcomes as well as a definition of tDCS therapeutic protocols for impulsive disorders.

Twenty Years of the Food Cravings Questionnaires: a Comprehensive Review

Purpose of Review

The Food Cravings Questionnaires (FCQs; Cepeda-Benito, Gleaves, Williams, & Erath, 2000) are among the most widely used instruments for measuring food cravings. In addition to the Food Cravings Questionnaire–Trait (FCQ–T) and the Food Cravings Questionnaire–State (FCQ–S), several modified versions have been developed as well. For their 20th anniversary, this article provides a comprehensive description of the FCQs and reviews studies on their psychometric properties and correlates.

Recent Findings

The FCQs and their modified versions have excellent internal reliability. Expectedly, the FCQ–T (and its derivatives) has higher retest-reliability than the FCQ–S as the FCQ–S is sensitive to situational changes such as food deprivation and food intake. However, while the FCQ–T is largely unaffected by such momentary states, it is also sensitive to change during weight-loss treatments and other interventions. Factor structure of the FCQ–T and FCQ–S has only partially been replicated. Construct validity of the FCQs is supported by experimental and longitudinal studies that measured food craving and food consumption in the laboratory and with ecological momentary assessment.

Summary

Numerous studies support reliability and validity of the FCQs and their modified versions, yet findings about their factor structures are inconsistent. Thus, using total scores or the short versions of the FCQs may be preferable.

Polarity Specific Effects of Cross-Hemispheric tDCS Coupled With Approach-Avoidance Training on Chocolate Craving

Transcranial Direct Current Stimulation (tDCS) over the Dorsolateral Prefrontal Cortex (DLPFC) has already been shown to decrease craving for food. However, it remains unclear whether a single session of tDCS combined with a cognitive bias modification (CBM) task may affect explicit and implicit measures of craving for chocolate. Fifty-one healthy volunteers (38 females; mean age: 22.12 ± 3.38) were randomly allocated to CBM training based on the Approach Avoidance task and either Sham, Right anodal-Left cathodal (RALC), or Left anodal-Right cathodal (LARC) tDCS. Results show that there was an increase in the explicit craving for chocolate, as assessed by the Visual Analog Scale [F(2, 46) = 3.239, p = 0.048], from the baseline to post-intervention. Participants which received LARC tDCS were explicitly self-reporting more craving for chocolate than those that received RALC tDCS (p = 0.023). Moreover, this effect was also observed on the implicit measure [F(2, 46) = 4.168, p = 0.022]. LARC tDCS significantly increased the implicit preference for chocolate when comparing to both RALC (p = 0.009) and Sham tDCS (p = 0.034). Previous studies have shown that RALC tDCS over the PFC is able to effectively decrease craving for food. Interestingly, the present data not only does not reproduce such result, but instead it suggests that LARC tDCS can actually increase the preference for chocolate. This result is compatible with recent models of brain laterality, in which cue craving seems to be more dependent on the left hemisphere. Thus, shifting the activity to the left hemisphere (while simultaneously reducing the activity over the homotopic region) may have led to this increased implicit as well as explicit preference for chocolate.

The effect of expectation on transcranial direct current stimulation (tDCS) to suppress food craving and eating in individuals with overweight and obesity

Transcranial direct current stimulation (tDCS) is a neuromodulation technique with potential to treat eating disorders and obesity. As for any potential treatment, it is important to assess the degree to which expectation effects contribute to its reported efficacy. This study assessed the effect of tDCS on amount of food craving and eating while tightly controlling treatment expectation. N = 74 adults with overweight or obesity were informed of the known effects of tDCS to suppress craving and eating. Once electrodes were on the head, half of the participants were told they were receiving real, and the other half sham tDCS. Within these groups, approximately half actually received real and the other half sham tDCS. Stimulation parameters used were those previously found to reduce craving and eating, including in our lab: 2 mA, anode right/cathode left targeting the dorsolateral prefrontal cortex for 20 min (real), or only for the first and last minute (sham). Analyses controlled for demographics, hunger, trait impulsiveness, eating motives, dieting, binge eating, suggestibility, and baseline craving and eating. Participants told they were receiving real tDCS craved and ate less than participants told they were receiving sham tDCS (both p < 0.01), regardless of tDCS condition administered. There was no main effect of real vs. sham tDCS on craving or eating or an interaction between tDCS condition and expectation. The scientific validation of tDCS as a treatment for eating-related conditions hinges on controlling for the powerful effects of expectation. This can include the type of information provided on consent forms and participants' ability to guess real from sham conditions.

Prefrontal brain stimulation during food-related inhibition training: effects on food craving, food consumption and inhibitory control

Modulation of dorsolateral prefrontal cortex (DLPFC) activity using non-invasive brain stimulation has been shown to reduce food craving as well as food consumption. Using a preregistered design, we examined whether bilateral transcranial direct current stimulation (tDCS) of the DLPFC could reduce food craving and consumption in healthy participants when administered alongside the cognitive target of inhibitory control training. Participants (N = 172) received either active or sham tDCS (2 mA; anode F4, cathode F3) while completing a food-related Go/No-Go task. State food craving, ad-lib food consumption and response inhibition were evaluated. Compared with sham stimulation, we found no evidence for an effect of active tDCS on any of these outcome measures in a predominantly female sample. Our findings raise doubts about the effectiveness of single-session tDCS on food craving and consumption. Consideration of individual differences, improvements in tDCS protocols and multi-session testing are discussed.

tDCS in Addiction and Impulse Control Disorders

The study of addiction and impulsion control disorders has shown that behaviors of seeking and consumption of addictive substances are subserved by neurobiological alterations specifically related to brain networks for reward, stress, and executive control, representing the brain's adaptation to the continued use of an addictive substance. In parallel, studies using neuromodulation techniques such as transcranial direct current stimulation (tDCS) have demonstrated promising effects in modulating cognitive and motor functions. This review aims to describe the neurobiology of addiction and some of the most relevant cognitive models of addictive behavior and to clarify how tDCS application modulates the intake and craving for several addictive substances, such as food, alcohol, nicotine, cocaine, crack, methamphetamine, and cannabis. We also discuss the positive and null outcomes of the use of this neuromodulatory technique in the treatment of addiction disorders resulting from the use of these substances. The reviewed findings lead us to conclude that tDCS interventions hold several promising clinical avenues in addiction and impulsive control. However, methodological investigations are necessary for undercover optimal parameters before implementing its clinical application.

Current state of the use of neuroimaging techniques to understand and alter appetite control in humans

PURPOSE OF REVIEW

It is in the brain where the decision is made what and how much to eat. In the last decades neuroimaging research has contributed extensively to new knowledge about appetite control by revealing the underlying brain processes. Interestingly, there is the fast growing idea of using these methods to develop new treatments for obesity and eating disorders. In this review, we summarize the findings of the importance of the use of neuropharmacology and neuroimaging techniques in understanding and modifying appetite control.

RECENT FINDINGS

Appetite control is a complex interplay between homeostatic, hedonic, and cognitive processes. Administration of the neuropeptides insulin and oxytocin curb food intake and alter brain responses in reward and cognitive control areas. Additionally, these areas can be targeted for neuromodulation or neurofeedback to reduce food cravings and increase self-control to alter food intake.

SUMMARY

The recent findings reveal the potential of intranasal administration of hormones or modifying appetite control brain networks to reduce food consumption in volunteers with overweight and obesity or individuals with an eating disorder. Although long-term clinical studies are still needed.

Got chocolate? Bilateral prefrontal cortex stimulation augments chocolate consumption

BACKGROUND

Understanding the mechanisms behind exerting self-control may reveal why health behaviors are resistant to change. Activity in the right inferior frontal gyrus (rIFG) plays a role in self-control processes and may be modulated using transcranial direct current stimulation (tDCS).

OBJECTIVE

In this early phase behavioral research study, we investigated whether anodal stimulation over the rIFG with cathodal stimulation over the left IFG (versus sham) reduced chocolate consumption.

METHODS

Twenty-three healthy females (ages 18-35) completed two tDCS sessions (2.0 mA vs. sham; order counterbalanced) in a within-subject, double-blind, randomized design with a 4-week washout. Participants were self-reported "chocolate cravers" and restrained eaters. Self-report assessments on disinhibited eating were completed at intake. Delay discounting and inhibitory control were assessed at the remaining visits. During stimulation, participants completed an inhibitory control training task (chocolate go/no-go task) and were randomized to the chocolate no-go condition (inhibit all responses to chocolate cues) or the control condition (inhibit responses to chocolate cues on half the trials). Following stimulation, participants completed a 15-min chocolate "taste test" with chocolate rating forms. Afterwards, staff measured the remaining chocolate to determine total consumption.

RESULTS

Contrary to our hypotheses, active tDCS significantly increased chocolate consumption vs. sham (mean = 43.2 vs. 32.2, p=0.005) in both task conditions, but had no effect on chocolate ratings (ps > 0.05). Higher delay discounting and self-reported disinhibited eating predicted greater consumption (ps < 0.05).

CONCLUSIONS

The results suggest widespread activation of the prefrontal cortex may reduce the ability to resist chocolate. Our data highlights important methodological considerations for conducting tDCS studies to target health behaviors.

Effect of transcranial direct current stimulation associated with hypocaloric diet on weight loss and metabolic profile in overweight or obesity: study protocol for a double-blind, randomized controlled clinical trial

BACKGROUND

Dietary interventions have limited success in promoting sustainable weight loss; new treatments allowing better compliance with hypocaloric diets should be developed. The aim of this trial is to describe the effects of a protocol combining repetitive active transcranial direct current stimulation (tDCS) with a hypocaloric diet on weight loss and food consumption in overweight or obese adults.

METHODS/DESIGN

Overweight or obese adults between 20 and 50 years of age with stable weight over the last 4 months will be selected for a 4-week randomized clinical trial of fixed-dose tDCS (20 sessions; 5 consecutive weekdays/wk, 2 mA, 20 minutes) over the right dorsolateral prefrontal cortex associated with a weight loss diet. The subjects will be randomly assigned in a 1:1 ratio and stratified by sex to active tDCS + diet or sham tDCS + diet. The study will be conducted at the Endocrine and Metabolism Unit of the Hospital de Clínicas de Porto Alegre, Brazil. The primary outcome is weight loss. Energy and macronutrient consumption, as well as adherence to the diet, will be assessed using 3-day weighed dietary records. Changes in blood glucose and plasma insulin will be assessed, and participants will complete self-report questionnaires to assess changes in mood and food behavior. All analyses will be done on a per-protocol and intention-to-treat basis.

DISCUSSION

This study explores the potential role of tDCS as an adjunctive treatment with a hypocaloric diet for obesity management.

TRIAL REGISTRATION

ClinicalTrials.gov , NCT02683902 . Registered on 11 January 2016.

Is transcranial direct current stimulation an effective modality in reducing food craving? A systematic review and meta-analysis

Non-invasive electrical stimulation of the brain has recently been extensively investigated to regulate food craving. However, the existing literature is controversial and there are some important questions which need to be addressed about clinical and technical factors contributing to efficacy of this method. A systematic search was performed in reliable scientific databases, and 15 eligible studies were identified. The pooled standardized mean differences for the effects of transcranial direct current stimulation (tDCS) on Visual Analogue Scale, energy intake and food craving questionnaire were -0.78 [-1.12, -0.44], -0.91 [-1.38, -0.44], -0.54 [-0.85, -0.24], respectively. Subgroup analysis showed that the most important factors associated with the impact of tDCS on food craving were the population under study, current intensity of stimulation, and number of stimulation sessions. The findings of this study support a significant impact of neuromodulation of dorsolateral prefrontal cortex (DLPFC) on energy intake and food craving using tDCS. It is recommended that multisession bilateral stimulation of the DLPFC with the current intensity of 2 mA be used to reduce food craving.

Chronic Stress and Impulsive Risk-Taking Predict Increases in Visceral Fat over 18 Months

OBJECTIVE

The aim of this study was to examine whether baseline chronic stress and impulsive risk-taking synergistically predict changes in visceral fat among healthy mothers in an observational, longitudinal, 18-month study.

METHODS

A prospective cohort of 113 adult women (age, mean ± SD: 42.83 ± 4.70; BMI, mean ± SD: 24.86 ± 4.32; 74%, n = 84 white) completed assessments at baseline and 18-month follow-up. Chronically stressed mothers caring for a child with an autism spectrum disorder ("caregivers"; n = 72 participants) were compared with lower stress mothers caring for a neurotypical child ("controls"; n = 41). This study objectively assessed impulsive risk-taking by using the Behavioral Analog Risk Task at baseline and assessed visceral fat at baseline and 18-month follow-up by using bioelectrical impedance (ViScan; Tanita Corporation, Tokyo, Japan).

RESULTS

The interaction of baseline chronic caregiving stress and impulsive risk-taking predicted an 18-month change in visceral fat, such that greater impulsive risk-taking was associated with greater 18-month increases in visceral fat among caregivers (ß = 0.423; P = 0.005) but not among controls (ß = -0.030; P = 0.802), both in unadjusted models and after accounting for covariates. Neither chronic stress nor impulsive risk-taking independently predicted 18-month changes in visceral fat.

CONCLUSIONS

The combination of high chronic stress and high impulsive risk-taking may increase risk for visceral fat gain over time and therefore may be an important intervention target in obesity prevention.

Obesity, Appetite, and the Prefrontal Cortex

PURPOSE OF REVIEW

Obesity is a chronic illness and its prevalence is growing worldwide and numerous factors play a role in the regulation of food intake. The prefrontal cortex (PFC) is involved in high-order executive function, regulation of limbic reward regions, and the inhibition of impulsive behaviors. Understanding the role of the PFC in the control of appetite regulation may contribute to a greater understanding of the etiology of obesity and could improve weight loss outcomes.

RECENT FINDINGS

Neuroimaging studies have identified lower activation in the left dorsolateral PFC (DLPFC) in obese compared to lean individuals and others have focused on efforts to improve cognitive control in this area of the brain. The DLPFC is a critical brain area associated with appetitive control, food craving, and executive functioning, indicating a candidate target area for treatment. Further studies are needed to advance our understanding of the relationship between obesity, appetite, and the DLPFC and provide validation for the effectiveness of novel treatments in clinical populations.

Affective Processing in Non-invasive Brain Stimulation Over Prefrontal Cortex

The prefrontal cortex (PFC) is the most frequently targeted brain region by non-invasive brain stimulation (NBS) studies. Non-invasively stimulating the PFC has been shown to both modulate affective processing and improve the clinical symptoms of several psychiatric disorders, such as depression and schizophrenia. The magnitude of the modulation depends on several factors, including the stimulation frequency, the number of stimulation sessions, and the specific sub-region of the PFC that is stimulated. Although some of the potential underlying mechanisms have been identified, the exact mechanisms that underlie these cognitive and affective changes remain unclear. The present review aims to summarize recent advances in the study of affective processing using NBS over the PFC. We will provide a theoretical framework for better understanding how affective processing changes are induced by NBS, with the goal of providing testable hypotheses for future studies.