Ketamine reduces the neural distinction between self- and other-produced affective touch: a randomized double-blind placebo-controlled study.

A coherent sense of self is crucial for social functioning and mental health. The N-methyl-D-aspartate antagonist ketamine induces short-term dissociative experiences and has therefore been used to model an altered state of self-perception. This randomized double-blind placebo-controlled cross-over study investigated the mechanisms for ketamine's effects on the bodily sense of self in the context of affective touch. Thirty healthy participants (15 females/15 males, age 19-39) received intravenous ketamine or placebo while performing self-touch and receiving touch by someone else during functional MRI - a previously established neural measure of tactile self-other-differentiation. Afterwards, tactile detection thresholds during self- and other-touch were assessed, as well as dissociative states, interoceptive awareness, and social touch attitudes. Compared to placebo, ketamine administration elicited dissociation and reduced neural activity associated with self-other-differentiation in the right temporoparietal cortex, which was most pronounced during other-touch. This reduction correlated with ketamine-induced reductions in interoceptive awareness. The temporoparietal cortex showed higher connectivity to somatosensory cortex and insula during other- compared to self-touch. This difference was augmented by ketamine, and correlated with dissociation strength for somatosensory cortex. These results demonstrate that disrupting the self-experience through ketamine administration affects neural activity associated with self-other-differentiation in a region involved in touch perception and social cognition, especially with regard to social touch by someone else. This process may be driven by ketamine-induced effects on top-down signaling, rendering the processing of predictable self-generated and unpredictable other-generated touch more similar. These findings provide further evidence for the intricate relationship of the bodily self with the tactile sense.

Ghrelin decreases sensitivity to negative feedback and increases prediction-error related caudate activity in humans, a randomized controlled trial.

The stomach-derived hormone ghrelin plays not only a role in feeding, starvation, and survival, but it has been suggested to also be involved in the stress response, in neuropsychiatric conditions, and in alcohol and drug use disorders. Mechanisms related to reward processing might mediate ghrelin's broader effects on complex behaviors, as indicated by animal studies and mostly correlative human studies. Here, using a within-subject double-blind placebo-controlled design with intravenous ghrelin infusion in healthy volunteers (n = 30), we tested whether ghrelin alters sensitivity to reward and punishment in a reward learning task. Parameters were derived from a computational model of participants' task behavior. The reversal learning task with monetary rewards was performed during functional brain imaging to investigate ghrelin effects on brain signals related to reward prediction errors. Compared to placebo, ghrelin decreased punishment sensitivity (t = -2.448, p = 0.021), while reward sensitivity was unaltered (t = 0.8, p = 0.43). We furthermore found increased prediction-error related activity in the dorsal striatum during ghrelin administration (region of interest analysis: t-values ≥ 4.21, p-values ≤ 0.044). Our results support a role for ghrelin in reward processing that extends beyond food-related rewards. Reduced sensitivity to negative outcomes and increased processing of prediction errors may be beneficial for food foraging when hungry but could also relate to increased risk taking and impulsivity in the broader context of addictive behaviors.

Assessing Childhood Maltreatment Exposure in Patients Without and With a Diagnosis of Substance Use Disorder.

OBJECTIVES: Childhood maltreatment (CM), widely held as a risk factor for substance use disorders (SUDs), is commonly assessed using the Childhood Trauma Questionnaire (CTQ). Retrospective self-reports are, however, potentially subject to bias. We used a unique patient sample with prospectively documented CM to examine the performance of the CTQ and how this is affected by the presence of SUD. METHODS: Analysis was based on a total of 104 individuals. Subjects with prospectively recorded CM were identified from a specialized childhood trauma unit in Linköping, Sweden (n = 55; 31 with SUD, 61% females; 24 without SUD, 71% females). Clinical controls had SUD but no CM (n = 25, 48% females). Healthy controls had neither SUD nor CM (n = 24, 54% females). We analyzed the agreement between retrospective CTQ scores and prospectively documented CM by κ analysis and assessed the performance of the CTQ to identify CM exposure using receiver operating characteristic (ROC) analysis. RESULTS: Agreement between prospectively and retrospectively recorded CM exposure was poor for sexual abuse (36.6%, Cohen κ = 0.32, P = 0.008) and physical abuse (67.3%, κ = 0.35, P = 0.007). Overall CTQ performance was fair (ROC: area under the ROC curve = 0.78, optimal cutoff = 36.5, sensitivity = 0.65, specificity = 0.75). However, performance was excellent in the absence of SUD (area under the ROC curve = 0.93, cutoff = 32.0, sensitivity = 0.88, specificity = 0.88), but poor in participants with lifetime SUD (area under the ROC curve = 0.62, cutoff = 42.0, sensitivity = 0.60, specificity = 0.36). CONCLUSIONS: These data support the CTQ as a tool to assess CM exposure but suggest that it may be less useful in patients with SUD.

A randomized controlled experimental medicine study of ghrelin in value-based decision making.

BACKGROUNDThe stomach-derived hormone ghrelin stimulates appetite, but the ghrelin receptor is also expressed in brain circuits involved in motivation and reward. We examined ghrelin effects on decision making beyond food or drug reward using monetary rewards.METHODSThirty participants (50% women and 50% men) underwent 2 fMRI scans while receiving i.v. ghrelin or saline in a randomized counterbalanced order.RESULTSStriatal representations of reward anticipation were unaffected by ghrelin, while activity during anticipation of losses was attenuated. Temporal discounting rates of monetary reward were lower overall in the ghrelin condition, an effect driven by women. Discounting rates were inversely correlated with neural activity in a large cluster within the left parietal lobule that included the angular gyrus. Activity in an overlapping cluster was related to behavioral choices and was suppressed by ghrelin.CONCLUSIONThis is, to our knowledge, the first human study to extend the understanding of ghrelin's significance beyond the canonical feeding domain or in relation to addictive substances. Contrary to our hypothesis, we found that ghrelin did not affect sensitivity to monetary reward anticipation, but rather resulted in attenuated loss aversion and lower discounting rates for these rewards. Ghrelin may cause a motivational shift toward caloric reward rather than globally promoting the value of reward.TRIAL REGISTRATIONEudraCT 2018-004829-82.FUNDINGSwedish Research Council (2013-07434), Marcus and Marianne Wallenberg foundation (2014.0187) and National Institute on Drug Abuse/National Institute on Alcohol Abuse and Alcoholism Intramural Research Program.

Resilience to substance use disorder following childhood maltreatment: association with peripheral biomarkers of endocannabinoid function and neural indices of emotion regulation.

Childhood maltreatment (CM) is a risk factor for substance use disorders (SUD) in adulthood. Understanding the mechanisms by which people are susceptible or resilient to developing SUD after exposure to CM is important for improving intervention. This case-control study investigated the impact of prospectively assessed CM on biomarkers of endocannabinoid function and emotion regulation in relation to the susceptibility or resilience to developing SUD. Four groups were defined across the dimensions of CM and lifetime SUD (N = 101 in total). After screening, participants completed two experimental sessions on separate days, aimed at assessing the behavioral, physiological, and neural mechanisms involved in emotion regulation. In the first session, participants engaged in tasks assessing biochemical (i.e., cortisol, endocannabinoids), behavioral, and psychophysiological indices of stress and affective reactivity. During the second session, the behavioral and brain mechanisms associated with emotion regulation and negative affect were investigated using magnetic resonance imaging. CM-exposed adults who did not develop SUD, operationally defined as resilient to developing SUD, had higher peripheral levels of the endocannabinoid anandamide at baseline and during stress exposure, compared to controls. Similarly, this group had increased activity in salience and emotion regulation regions in task-based measures of emotion regulation compared to controls, and CM-exposed adults with lifetime SUD. At rest, the resilient group also showed significantly greater negative connectivity between ventromedial prefrontal cortex and anterior insula compared to controls and CM-exposed adults with lifetime SUD. Collectively, these peripheral and central findings point to mechanisms of potential resilience to developing SUD after documented CM exposure.

Re-examining the link between childhood maltreatment and substance use disorder: a prospective, genetically informative study.

Childhood maltreatment is considered a risk factor for substance use disorders (SUD), but this is largely based on retrospective self-reports that are subject to recall bias, designs that do not control for familial confounding, or both. The specific contribution of childhood maltreatment to SUD risk thus remains unclear. Here, we evaluated this contribution in a prospective cohort with objectively recorded childhood maltreatment, using a design that allows controlling for familial confounding. We used medical records and registers to study 525 young adults (20-37 years) with prospectively and objectively documented severe maltreatment exposure, 1979 clinical controls (unexposed former child and adolescent psychiatry patients), 1388 matched healthy controls; and their siblings and cousins. We examined the association between maltreatment and SUD using Cox regression models in the population, as well as stratified within siblings in the same family. SUD risk was significantly increased with childhood maltreatment exposure (crude HR: 6.61, 95% CI: 5.81-7.53; HR adjusted for sex, birthyear, externalizing problems, parents' SUD and socioeconomic factors: 3.50, 95% CI 2.95, 4.16). An approximately threefold elevated SUD risk remained when comparing exposed individuals with their unexposed siblings (adjusted HR: 3.12, 95% CI 2.21, 4.42). We provide estimates of the association between childhood maltreatment and SUD accounting for possible confounds of both recall bias and familial factors. When familial confounding is controlled for, SUD risk attributable to severe childhood maltreatment is decreased, but nevertheless considerable. These findings establish a specific contribution of childhood maltreatment to SUD, underscoring the need for SUD prevention in young people exposed to maltreatment.

Using quantitative trait in adults with ADHD to test predictions of dual-process theory.

Dual-process theory is a widely utilized modelling tool in the behavioral sciences. It conceptualizes decision-making as an interaction between two types of cognitive processes, some of them fast and intuitive, others slow and reflective. We make a novel contribution to this literature by exploring differences between adults with clinically diagnosed ADHD and healthy controls for a wide range of behaviors. Given the clinical picture and nature of ADHD symptoms, we had a strong a priori reason to expect differences in intuitive vs reflective processing; and thus an unusually strong case for testing the predictions of dual-process theory. We found mixed results, with overall weaker effects than expected, except for risk taking, where individuals with ADHD showed increased domain sensitivity for gains vs losses. Some of our predictions were supported by the data but other patterns are more difficult to reconcile with theory. On balance, our results provide only limited empirical support for using dual-process theory to understand basic social and economic decision-making.

Comorbidity of Adult ADHD and Its Subtypes With Substance Use Disorder in a Large Population-Based Epidemiological Study.

Objective: The objective of the study is to explore the role and possible substance preference in ADHD and subtypes in substance use disorder (SUD). Method: Using self-report data on ADHD Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV) symptoms and SUD (alcohol, illicit drugs, and nicotine) in 18,167 Swedish twins, aged 20 to 45 years, we obtained odds ratios (OR) from mixed effect logistic regression, controlling for age, sex, education, and nonindependence of twin data. Results: Increased ADHD symptoms were significantly associated with increased odds for all SUD. ORs ranged between 1.33 for regular nicotine (95% confidence interval [CI] = [1.12, 1.59]); 2.54 for multiple drug use (95% CI = [2.00, 3.23]), and 3.58 for alcohol dependence (95% CI = [2.86, 4.49]). Conclusion: ADHD symptoms and subtypes in the population are associated with increased risks for all SUD outcomes, with no difference between ADHD subtypes, no substance preference, and no sex differences for the comorbidity. Clinicians need to consider ADHD evaluation and treatment as part of management of SUD in adults.

Genetic and environmental contributions to the association between attention deficit hyperactivity disorder and alcohol dependence in adulthood: A large population-based twin study.

Previous research indicates that attention deficit hyperactivity disorder (ADHD) frequently co-occurs with alcohol dependence; however, the extent to which shared genetic risk factors underpin this association remains unclear. The aim of this study is to investigate the relative importance of genetic, shared, and nonshared environmental factors for the overlap between ADHD and alcohol dependence in adults. Almost 18,000 adult twins aged 20-45 years, from more than 12,000 twin pairs (5,420 complete pairs), from the population-representative Swedish Twin Registry, were included. Self-ratings were used to assess symptoms of ADHD and alcohol dependence. Twin analysis was used to determine the role of additive genetic (A), shared (C), and nonshared environmental (E) factors. As a result, we found a significant association between ADHD and alcohol dependence (odds ratio 3.58; 95% confidence interval, 2.85-4.49). Twin analysis suggested that shared genetic risk factors explained 64% of the overlap between ADHD and alcohol dependence. Nonshared environmental factors accounted for the remaining 36%, whereas the contribution of shared environmental factors was minimal. We found no support for statistically significant sex differences in the overlap between ADHD and alcohol dependence. In conclusion the overlap between ADHD and alcohol dependence in adulthood was largely explained by shared genetic risk factors. This is an important step toward understanding the underlying nature of the risk of alcohol dependence in patients with ADHD and suggests that individuals with ADHD and their family members are important targets for alcohol prevention and treatment. © 2015 Wiley Periodicals, Inc.