Natalie J. Loxton

The role of impulsivity in the development of substance use and eating disorders

Impulsivity is now widely viewed as a multidimensional construct consisting of a number of related dimensions. Although many measures of impulsivity are correlated, most recent factor analyses support at least a two-factor model. In the current paper, these two factors have been labelled reward sensitivity, reflecting one of the primary dimensions of Grays personality theory, and rash-spontaneous impulsiveness. The evidence supporting the existence of two dimensions of impulsivity is reviewed in relation to substance misuse and binge eating.

The relationship between sociocultural pressure to be thin and body dissatisfaction in preadolescent girls

This study investigates the relationships among sociocultural pressures to be thin, internalisation of the thin ideal, social comparison, body mass index, and body dissatisfaction in young girls. One hundred and fifty-three 10-13 year old girls completed measures assessing sociocultural pressure to be thin, media exposure, body dissatisfaction, social comparison, and internalisation of the thin ideal. Although sociocultural factors, as a group, were significantly associated with internalisation of the thin ideal, perceived media pressure was the only sociocultural influence uniquely related to internalisation of the thin ideal. Perceived pressure to be thin delivered by the media was found to be associated with body dissatisfaction via internalisation of the thin ideal. The relationship between internalisation of the thin ideal and body dissatisfaction was also partially influenced by social comparison. Body mass was found to have a direct association with body dissatisfaction. A model incorporating the relationships among media pressure, internalisation of the thin ideal, social comparison, and body dissatisfaction is proposed.

Does the tendency to act impulsively underlie binge eating and alcohol use problems? An empirical investigation

The co-occurrence of problem drinking and binge eating and purging has been well documented. However, there has been relatively little investigation of etiological models that may influence the development of this co-occurrence. This study tests the hypotheses that impulsivity is heightened in eating disordered women compared with controls, and that women with comorbid bulimia and alcohol use disorders show higher impulsivity than bulimic-only women. The Impulsivity scale, BIS/BAS scales, State Anxiety Inventory, and a behavioural measure of reward responsiveness (CARROT) were administered to 22 women with bulimia, 23 women with comorbid bulimia and alcohol abuse/dependence, and 21 control women. As hypothesised, eating disordered women scored higher than controls on several self-report measures of impulsivity and sorted cards faster during a financially rewarded trial on the behavioural task. Also, as predicted, comorbid women scored higher than bulimic women on the Impulsivity scale. These findings suggest that individual differences in impulsiveness and a tendency to approach rewarding stimuli may contribute to developing these disorders.

'Food addiction' and its association with a dopaminergic multilocus genetic profile

BACKGROUND Our objective was to employ a novel genetic methodology - whereby functional variants of the dopamine pathway were aggregated to reflect a polygenic liability - in the study of food addiction. We anticipated that the composite index of elevated dopamine signaling (a multilocus genetic profile score [MLGP]) would distinguish those with a designation of food addiction (according to the Yale Food Addiction Scale [YFAS] criteria), and age and weight equivalent controls. Our second aim was to assess whether this index was positively associated with eating-related sub-phenotypes of food addiction (e.g. binge eating and food cravings). METHODS Adults (n=120) recruited from the community were solicited for an overeating/overweight study. Eating-behavior questionnaires were completed and a blood sample was taken for genotyping. RESULTS AND CONCLUSIONS The YFAS identified 21 participants with food addiction. As predicted, the MLGP score was higher in those with YFAS-diagnosed food addiction, and it correlated positively with binge eating, food cravings, and emotional overeating. We then tested a multiple-mediation model proposing that reward-driven overeating facilitates the relationship between the MLGP score and food addiction. The model was statistically significant, supporting the view that the relationship between a composite genetic index of dopamine signaling and food addiction is mediated by certain aspects of reward-responsive overeating.

Impulsivity in Hong Kong-Chinese club-drug users

To investigate the relationship between personality, club-drug use and high-risk drug-related behaviour, 360 club-drug users and 303 non-drug users in Hong Kong were assessed on measures of two impulsivity dimensions, reward drive and rash impulsivity, and a related trait of punishment sensitivity. The most frequently used drugs were ketamine, ecstasy, and cannabis, with the majority of participants using two or more drugs on any one occasion. Club-drug users were more rash-impulsive and reward-driven, and less punishment-sensitive than non-drug users (p<0.001). Rash impulsivity, but not reward drive or punishment sensitivity, was significantly (p<0.001) associated with risky drug-related behaviour. There was no association between any personality traits and preferred drug. These findings suggest that, while those who use club drugs are generally more impulsive and less punishment-sensitive, some discrete facets of impulsivity are associated with differing patterns of drug-use behaviour.

Does negative mood drive the urge to eat? The contribution of negative mood, exposure to food cues and eating style

The current study investigated whether negative mood alone, or in conjunction with exposure to food cues, influences the urge to eat. Female participants (N=160) were allocated to either a negative or neutral mood induction procedure followed by exposure to either a preferred food cue or a non-food cue. Participants reported their urge to eat at baseline, following the mood induction procedure, and following the cue exposure, as well as completing measures of restrained and disinhibited eating. Contrary to prediction, urge to eat decreased following the mood induction procedure for those in the negative mood condition. This was not influenced by eating style (i.e., restrained or disinhibited eaters). Urge to eat subsequently increased following exposure to the food, but not the non-food, cue. This effect was moderated by negative mood and eating style with disinhibited eating being positively associated with urge to eat for those women in the negative mood condition. These findings suggest that negative mood plays a role in the tendency to overeat, but only in the context of personally desirable food cues and for a subgroup of women with a history of disinhibited eating.

Addictive behaviors and addiction-prone personality traits: Associations with a dopamine multilocus genetic profile

The purpose of this study was to examine reward-related genetic risk for addictive behaviors in a healthy community sample (n=217) of men and women. We tested a mediation model predicting that a quantitative multilocus genetic profile score - reflecting the additive effects of alleles known to confer relatively increased dopamine signaling in the ventral striatum - would relate positively to a composite measure of addictive behaviors, and that this association would be mediated by personality traits consistently associated with addiction disorders. Our model was strongly supported by the data, and accounted for 24% of the variance in addictive behaviors. These data suggest that brain reward processes tend to exert their influence on addiction risk by their role in the development of relatively stable personality traits associated with addictive behaviors.

Dependent heroin use and associated risky behaviour: The role of rash impulsiveness and reward sensitivity

Impulsive temperament has long been considered as a risk factor for substance use disorders (SUD). Considering the heterogeneity of impulsivity, a biologically-based 2-factor model incorporating reward sensitivity and rash impulsiveness facets, has been proposed. Here we report how these two facets of impulsiveness could be associated with different aspects of dependent heroin use and associated risky behaviour. Two hundred and ninety three dependent heroin users and 232 non-users were assessed on reward sensitivity, rash impulsivity, and the related trait of punishment sensitivity. After adjusting for multiple comparisons, heroin users were found to be more rash-impulsive and reward-sensitive than non-users (p<0.001). Within users, rash impulsivity was associated with high risk behaviour including escalating heroin consumption, injecting heroin use, hazardous drinking, low treatment-seeking and risky sexual behaviour. Reward sensitivity was uniquely associated with early onset of drug use. While greater impulsivity is a common trait in drug users compared with non-users, the use of a 2-factor model of impulsivity provides additional information regarding specific aspects of drug initiation and maintenance that can be targeted in the prevention and treatment of heroin dependence.

Great expectations. Eating expectancies as mediators of reinforcement sensitivity and eating

Eating expectancies are proposed as cognitive pathways linking reinforcement (reward and punishment) sensitivities and the tendency to over-eat in response to appetitive and emotional cues. In Study One (N=243 university women) explicit eating expectancies were tested as potential mediators of reinforcement sensitivities and eating styles. Broadly, expectancies that eating alleviates negative affect/boredom mediated both reward and punishment sensitivity and emotional eating. The expectancy that eating is pleasurable and rewarding mediated reward sensitivity and external eating. In Study Two (N=109), using an implicit eating expectancy task, reward sensitivity and external eating was mediated via positive expectancy statements, notably, that eating is pleasurable and rewarding. Reward sensitivity and emotional eating was mediated specifically by expectancies that eating manages boredom. Punishment sensitivity was not associated with any implicit expectancies. Findings support the role of expectancies as cognitive mediators in the relationship between reinforcement sensitivities and emotionally-driven versus externally-driven eating styles. However, the largely appetitive implicit expectancies task only supported an association with reward sensitivity.

The role of impulsive personality traits in the initiation, development, and treatment of substance misuse problems

Recent advances in the understanding of the genetic, neurochemical, behavioral and cultural underpinnings of addiction have led to rapid advances in the understanding of addiction as a disease. In fact, advances in basic science and the development of new pharmacological and behavioral therapies associated with them are appearing faster than can be assimilated not only by clinical researchers but practitioners and policy makers as well. Translation of science-based addictions knowledge into improved prevention, assessment and treatment, and communication of these changes to researchers and practitioners are significant challenges to the field. The general aim of this book is to summarize current and potential linkages between advances in addiction science and innovations in clinical practice. Whilst this book is primarily focused on translation, it also encompasses some scientific advances that are relevant to dissemination, and the book is itself a tool for disseminating innovative thinking. The goal is to generate interest in application opportunities from both recent research and theoretical advances.