Improving substance use prevention efforts with executive function training

BACKGROUND

Executive function (EF) includes emotional regulation, planning and decision-making, and behavioral impulse control. Improving youth substance use (SU) prevention by targeting EF poses challenges including determining whether specific sub-domains of EF are more associated with SU than others, whether EF is related to some types of SU more than others, and whether EF programs might be enhanced by inclusion of mindfulness training.

METHODS

Data were drawn from two studies from the Pathways to Health project: a randomized controlled trial of 4th-6th graders and a cross-sectional pilot study of the relationship of EF to specific types of SU in a sample of 7th graders. Survey measures included assessment of the EF subdomains of inhibitory control (IC), emotional control, working memory, organization/planning, lifetime SU (tobacco and alcohol use), and mindfulness. Analyses included multivariate and multiple group path analysis.

RESULTS

Results suggested that the EF sub-domain of IC was the strongest and most consistent predictor of SU, particularly cigarette and e-cigarette use, though emotional control was predictive of alcohol use among late-elementary school students. In the 7th grade sample, IC was predictive of alcohol, cigarette, and e-cigarette use only among students in the low 75% of mindfulness.

CONCLUSIONS

Findings from the present studies suggest that improvements in SU prevention efforts may result from increased curricular emphasis on IC and its application to multiple substance use prevention, and systematically integrating mindfulness with EF skills training. Future research should examine whether EF-SU relationships vary across patterns of SU and types of measures used to assess EF.

Treating prolactinomas with dopamine agonists: always worth the gamble?

Dopamine agonists are the treatment of choice for all patients with prolactinomas. They are generally safe, effective, and well-tolerated. However, a link between their use and the development of impulse control disorders has been well recognized in the field of neurology for some time, and evidence for a similar effect in endocrine patients is emerging. This has mainly been revealed through clinical case reports, plus a small number of comparative studies of varying robustness. We review the current available literature and discuss the implications for clinical practice, in particular emphasizing the need for clinicians to be alert to these uncommon but serious adverse effects.

Women with borderline personality disorder do not show altered BOLD responses during response inhibition

Impulsivity is central to borderline personality disorder (BPD). Response inhibition, addressing the ability to suppress or stop actions, is one aspect of behavioral impulse control which is frequently used to assess impulsivity. BPD patients display deficits in response inhibition under stress condition or negative emotions. We assessed whether response inhibition and its neural underpinnings are impaired in BPD when tested in an emotionally neutral setting and when co-morbid attention-deficit/hyperactivity disorder (ADHD) is excluded. To this end, we studied response inhibition in unmedicated BPD patients and healthy controls (HC) in two independent samples using functional magnetic resonance imaging during Simon-, Go/nogo-, and Stopsignal tasks. BPD patients and HC did not differ significantly in their performance in the Go/nogo and the Stopsignal tasks. Response interference in the Simon task was increased in BPD patients in one sample, but this could not be replicated in the second sample. In both samples, no significant differences in brain activation patterns during any of the tasks were present while the neural impulse control network was robustly activated during the inhibition tasks in both groups. Our results provide evidence that under emotionally neutral conditions response inhibition is not impaired in patients with BPD without co-occurring ADHD.

Enhancing decision-making and cognitive impulse control with transcranial direct current stimulation (tDCS) applied over the orbitofrontal cortex (OFC): A randomized and sham-controlled exploratory study

BACKGROUND

Decision-making and impulse control (both cognitive and motor) are complex interrelated processes which rely on a distributed neural network that includes multiple cortical and subcortical regions. Among them, the orbitofrontal cortex (OFC) seems to be particularly relevant as demonstrated by several neuropsychological and neuroimaging investigations.

METHODS

In the present study we assessed whether transcranial direct current stimulation (tDCS) applied bilaterally over the OFC is able to modulate decision-making and cognitive impulse control. More specifically, 45 healthy subjects were randomized to receive a single 30-min session of active or sham anodal tDCS (1.5 mA) applied over either the left or the right OFC (coupled with contralateral cathodal tDCS). They were also assessed pre- and post-tDCS with a battery of computerized tasks.

RESULTS

Our results show that participants who received active anodal tDCS (irrespective of laterality), vs. those who received sham tDCS, displayed more advantageous decision-making (i.e., increased Iowa Gambling Task "net scores" [p = 0.04]), as well as improved cognitive impulse control (i.e., decreased "interference" in the Stroop Word-Colour Task [p = 0.007]). However, we did not observe tDCS-related effects on mood (assessed by visual analogue scales), attentional levels (assessed by the Continuous Performance Task) or motor impulse control (assessed by the Stop-Signal Task).

CONCLUSIONS

Our study potentially serves as a key translational step towards the development of novel non-invasive neuromodulation-based therapeutic interventions directly targeting vulnerability factors for psychiatric conditions such as suicidal behaviour and addiction.

MPTP-induced executive dysfunction is associated with altered prefrontal serotonergic function

In Parkinson's disease, cognitive deficits manifest as fronto-striatally-mediated executive dysfunction, with impaired attention, planning, judgment, and impulse control. We examined changes in executive function in mice lesioned with subchronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) using a 3-choice serial reaction-time (SRT) task, which included measures of sustained attention and impulse control. Each trial of the baseline SRT task comprised a pseudo-random pre-cue period ranging from 3 to 8 s, followed by a 1-s cue duration. MPTP impaired all measures of impulsive behavior acutely, but with additional training their performance normalized to saline control levels. When challenged with shorter cue durations, MPTP-lesioned mice had significantly slower reaction times than wild-type mice. When challenged with longer pre-cue times, the MPTP-lesioned mice exhibited a loss of impulse control at the longer durations. In lesioned mice, striatal dopamine was depleted by 54% and the number of tyrosine-hydroxylase-positive neurons in the substantia nigra pars compacta was reduced by 75%. Serotonin (5-HT) was unchanged in the striatum and prefrontal cortex (PFC), but the ratio of 5-hydroxyindolacetic acid (5-HIAA) to 5-HT was significantly reduced in the MPTP group in the PFC. In lesioned mice, prefrontal 5-HIAA/5-HT was significantly correlated with the executive impairments and striatal norepinephrine was associated with slower reaction times. None of the neurochemical measures was significantly associated with behavior in saline-treated controls. Taken together, these results show that prefrontal 5-HT turnover may play a pivotal role in MPTP-induced executive dysfunction.

Hypersexuality in Parkinson's Disease: Systematic Review and Report of 7 New Cases

Hypersexuality (HS) was one of the earliest examples of an impulse control disorder (ICD) or behavior to be associated with treatment for Parkinson's disease (PD), with an estimated prevalence of approximately 3.5%. Here, we report on a systematic review of the published literature of HS in PD with a view to uncovering evidence as to whether it is distinct from other ICDs. In addition, we report on 7 new cases that had broad neuropsychological testing, including a gambling test, which taps into reward and inhibitory mechanisms. The review uncovered a number of case series and cohorts that comment on the prevalence of HS, but very few made systematic comparisons with other ICDs, although younger onset and male sex are usually noted. A few studies have begun to map out a neuropsychological profile for HS, and our own cases show particular deficits in learning from negative outcomes, but, overall, there are insufficient data to draw firm conclusions. Functional imaging has shown patterns of increased content-specific activation in response to sexual material and this might relate to increased dopamine release. We conclude with a brief survey of the neurobiology of sexuality, which suggests possible avenues for further research and treatment of HS.

Variants in Ion Channel Genes Link Phenotypic Features of Bipolar Illness to Specific Neurobiological Process Domains

Recent advances in genome-wide association studies are pointing towards a major role for voltage-gated ion channels in neuropsychiatric disorders and, in particular, bipolar disorder (BD). The phenotype of BD is complex, with symptoms during mood episodes and deficits persisting between episodes. We have tried to elucidate the common neurobiological mechanisms associated with ion channel signaling in order to provide a new perspective on the clinical symptoms and possible endophenotypes seen in BD patients. We propose a model in which the multiple variants in genes coding for ion channel proteins would perturb motivational circuits, synaptic plasticity, myelination, hypothalamic-pituitary-adrenal axis function, circadian neuronal rhythms, and energy regulation. These changes in neurobiological mechanisms would manifest in endophenotypes of aberrant reward processing, white matter hyperintensities, deficits in executive function, altered frontolimbic connectivity, increased amygdala activity, increased melatonin suppression, decreased REM latency, and aberrant myo-inositol/ATP shuttling. The endophenotypes result in behaviors of poor impulse control, motivational changes, cognitive deficits, abnormal stress response, sleep disturbances, and energy changes involving different neurobiological process domains. The hypothesis is that these disturbances start with altered neural circuitry during development, following which multiple environmental triggers may disrupt the neuronal excitability balance through an activity-dependent molecular process, resulting in clinical mood episodes.

Management of impulse control disorders in Parkinson's disease: Controversies and future approaches

Impulse control disorders in Parkinson's disease are a group of impulsive behaviors most often associated with dopaminergic treatment. Presently, there is a lack of high quality evidence available to guide their management. This manuscript reviews current management strategies, before concentrating on the concept of dopamine agonist withdrawal syndrome and its implications for the management of impulse control disorders. Further, we focus on controversies, including the role of more recently available anti-parkinsonian drugs, and potential future approaches involving routes of drug delivery, nonpharmacological treatments (such as cognitive behavioral therapy and deep brain stimulation), and other as yet experimental strategies.

Behavioral effects of levodopa

In recent years, levodopa-induced behavioral changes have received increased attention in the medical literature and in clinical practice. The spectrum of these symptoms includes non-motor fluctuations with neuropsychiatric symptoms, compulsive behaviors such as punding, dopamine dysregulation syndrome, and impulse control disorders, psychosis and hallucinations, as well as hypomania and mania. Despite knowledge of the clinical features associated with these behaviors, many of them are probably underdiagnosed. Although the mechanisms underlying behavioral symptoms are still incompletely understood, recent data from imaging and pathological studies have increased our understanding and guided new treatment strategies. Appropriate management remains challenging, because reduction of levodopa (l-dopa) and dopaminergic treatment is often recommended; however, doses required for control of motor symptoms may still induce behavioral changes. Newer modes of delivery of dopaminergic treatment, deep brain stimulation, and nondopaminergic agents may either provide alternatives for treatment of these behavioral problems or permit treatment of parkinsonism with less risk of these behavioral disorders.

Nucleus accumbens core and shell inactivation differentially affects impulsive behaviours in rats

Impulsivity is a multifactorial phenomenon, determined by deficits in decision-making (impulsive choice) and impulse control (impulsive action). Recent findings indicate that impulsive behaviour is not only top-down controlled by cortical areas, but also modulated at subcortical level. The nucleus accumbens (NAc) might be a key substrate in cortico-limbic-striatal circuits involved in impulsive behaviour. Dissociable effects of the NAc subregions in various behavioural paradigms point to a potential functional distinction between NAc core and shell concerning different types of impulsivity. The present study used reversible inactivation of the rats' NAc core and shell via bilateral microinfusion of the GABAA receptor agonist muscimol (0.05μg/0.3μl) and fluorophore-conjugated muscimol (FCM, 0.27μg/0.3μl) in order to study their contribution to different aspects of impulse control in a 5-choice serial reaction time task (5-CSRTT) and impulsive choice in a delay-based decision-making T-maze task. Acute inactivation of NAc core as well as shell by muscimol increased impulsive choice, with higher impairments of the rats' waiting capacity in the T-maze following core injections compared to shell. Intra-NAc shell infusion of muscimol also induced specific impulse control deficits in the 5-CSRTT, while deactivation of the core caused severe general impairments in task performance. FCM did not affect animal behaviour. Our findings reveal clear involvement of NAc shell in both forms of impulsivity. Both subareas play a key role in the regulation of impulsive decision-making, but show functional dichotomy regarding impulse control with the core being more implicated in motivational and motor aspects.

Dissociating the influence of response selection and task anticipation on corticospinal suppression during response preparation

Motor behavior requires selecting between potential actions. The role of inhibition in response selection has frequently been examined in tasks in which participants are engaged in some advance preparation prior to the presentation of an imperative signal. Under such conditions, inhibition could be related to processes associated with response selection, or to more general inhibitory processes that are engaged in high states of anticipation. In Experiment 1, we manipulated the degree of anticipatory preparation. Participants performed a choice reaction time task that required choosing between a movement of the left or right index finger, and used transcranial magnetic stimulation (TMS) to elicit motor evoked potentials (MEPs) in the left hand agonist. In high anticipation blocks, a non-informative cue (e.g., fixation marker) preceded the imperative; in low anticipation blocks, there was no cue and participants were required to divide their attention between two tasks to further reduce anticipation. MEPs were substantially reduced before the imperative signal in high anticipation blocks. In contrast, in low anticipation blocks, MEPs remained unchanged before the imperative signal but showed a marked suppression right after the onset of the imperative. This effect occurred regardless of whether the imperative had signalled a left or right hand response. After this initial inhibition, left MEPs increased when the left hand was selected and remained suppressed when the right hand was selected. We obtained similar results in Experiment 2 except that the persistent left MEP suppression when the left hand was not selected was attenuated when the alternative response involved a non-homologous effector (right foot). These results indicate that, even in the absence of an anticipatory period, inhibitory mechanisms are engaged during response selection, possibly to prevent the occurrence of premature and inappropriate responses during a competitive selection process.

Impaired facilitation of self-control cognition by glucose in patients with schizophrenia: a randomized controlled study

OBJECTIVE

Studies in healthy individuals show that exerting self-control consumes cognitive resources, which reduces subsequent self-control performance. Restoring the availability of blood glucose eliminates this impairment. Patients with schizophrenia are found to have self-regulatory dysfunctions. This study aims to investigate whether patient's (a) glucose facilitation effects will be impaired, and (b) will have exaggerated depletion in a self-control task.

METHOD

40 patients with schizophrenia-spectrum disorders and 40 normal controls were recruited. A two drinks (glucose vs. placebo)×two depleting phases (self-control depleted vs. non-depleted) between-groups design was used. We examined the blood glucose levels before and after the selfcontrol depletion phase and the subsequent performances in two self-control tasks (handgrip and Stroop tests) after the drink condition.

RESULTS

The four groups (depleting×glucose, depleting×placebo, non-depleting×glucose and nondepleting×placebo) of both patients and normal controls were comparable on a number of characteristics. The change in blood glucose level in the depleting group was significantly different from those in the non-depleting group. Two×two between-subjects ANOVAs were carried out to test the performances in the handgrip and Stroop tasks. Significant interactions were found in healthy controls regarding both tasks. However, a significant interaction was only found in patients regarding the handgrip task but not the Stroop task.

CONCLUSIONS

This study demonstrated an abnormal glucose facilitation effect in patients during a cognitive self-control task but not during a physical self-control task. The findings also suggested for the first time that a self-control depletion effect is intact in patients with schizophrenia.

Differences in self-reported and behavioral measures of impulsivity in recreational and dependent cocaine users

BACKGROUND

Dependent cocaine users consistently display increased trait impulsivity on self-report questionnaires and less consistently exhibit elevated motor impulsivity in some behavioral tasks. However, trait and behavioral impulsivity measures have rarely been investigated in recreational users. Therefore, we examined self-reported trait and motor impulsivities in recreational and dependent cocaine users to clarify the role of impulse control in cocaine addiction and non-dependent cocaine use.

METHODS

We investigated relatively pure recreational (n=68) and dependent (n=30) cocaine users, as well as psychostimulant-naïve controls (n=68), with self-report questionnaires (Barratt Impulsiveness Scale 11; Temperament and Character Inventory) and behavioral tasks (Rapid Visual Information Processing Task; Stop-Signal Task).

RESULTS

Compared with controls, recreational and dependent cocaine users displayed higher trait impulsivity and novelty seeking scores on self-report questionnaires. Trait impulsivity scores were strongly associated with an increased number of symptoms of depression and attention deficit hyperactivity disorder and correlated significantly with long-term cocaine intake parameters. By contrast, none of the behavioral motor impulsivity measures showed significant group effects or correlated with cocaine use parameters. The correlations among the self-report measures were high, but self-reports were scarcely correlated with behavioral task measures.

CONCLUSIONS

These findings suggest that relatively pure cocaine users already display increased trait impulsivity at a recreational level of use. However, the results do not indicate any cocaine-related elevation of behavioral impulsivity in terms of motor or response inhibition. In summary, our data imply that elevated trait impulsivity is not a specific feature of dependent cocaine use.

Impulsive behavior and recurrent major depression associated with dandy-walker variant

Reported herein is a case of recurrent major depression with impulse control difficulty in a 33-year-old man with Dandy-Walker variant. He was diagnosed as having major depressive disorder a year before he presented himself to the authors' hospital, and had a history of three-time admission to a psychiatric unit in the previous 12 months. He was readmitted and treated with sodium valporate 1,500 mg/day, mirtazapine 45 mg/day, and quetiapine 800 mg/day during the three months that he was confined in the authors' hospital, and the symptoms were reduced within three months but remained thereafter. This is the only case so far reporting recurrent depression with impulse control difficulty associated with Dandy-Walker variant. This case implies that any cerebellar lesion may cause the appearance of recurrent depression with impulse control difficulty in major depressive disorder.

Effect of modafinil on impulsivity and relapse in alcohol dependent patients: a randomized, placebo-controlled trial

Poor impulse control plays an important role in the development, course and relapse of substance use disorders. Therefore, improving impulse control may represent a promising approach in the treatment of alcohol dependence. This study aimed to test the effect of modafinil on impulse control and alcohol use in alcohol dependent patients (ADP) in a randomized, double-blind, placebo-controlled trial. Eighty-three abstinent ADP were randomized to 10 weeks modafinil (300 mg/d) or placebo. Alcohol use was quantified using the timeline follow-back method and was assessed until 6 months after treatment discontinuation. Impulsivity was assessed using self-report questionnaires (Barratt Impulsiveness Scale; State Impulsivity questionnaire) and neurocognitive tasks (Stop Signal Task; Delay Discounting Task) administered before, during and after treatment. Modafinil significantly improved self-report measures of state impulsivity, but had no effect on percentage of abstinent days or percentage of heavy drinking days, nor on the behavioral measures of impulsivity. However, subgroup analysis revealed that modafinil prolonged the time to relapse (p=.022) and tended to increase the percentage of abstinent days (p=.066) in ADP with poor response inhibition at baseline, whereas modafinil increased the percentage of heavy drinking days (p=.003) and reduced the percentage of abstinent days (p=.002) in patients with better baseline response inhibition. Overall results do not favor the use of modafinil in order to reduce relapse or relapse severity in ADP, and caution is required in prescribing modafinil to a non-selected sample of ADP. Further research on the effect of modafinil in ADP with poor baseline response inhibition is warranted.

Sleep, impulse control, and sensation-seeking predict delinquent behavior in adolescents, emerging adults, and adults

PURPOSE

The present study examined delinquent behavior from adolescence into adulthood within the dual systems model of adolescent risk-taking, which identifies maturational patterns of socioemotional and cognitive control systems as predictors of risk-taking. The role of sleep was also investigated within the relationship.

METHODS

Hierarchical regression and path analysis examined delinquency at three waves (1996, 2001, and 2008) of the National Longitudinal Study of Adolescent Health.

RESULTS

Impulse control and sensation-seeking predicted concurrent delinquent behavior at all three waves, demonstrating the developmental shift as described within the dual systems model in which the relative contribution of sensation-seeking decreases from adolescence into adulthood, whereas the relative contribution of impulse control improves. Data also revealed that sleep duration and delayed bedtimes had both direct and indirect associations with delinquent behavior during adolescence; sleep duration did not directly predict such activity during later waves.

CONCLUSION

The dual systems model of adolescent risk-taking appears to be predictive of delinquent behavior during adolescence and the transition into adulthood. Preliminary findings suggest the importance of considering both adolescent sleep and cognitive and socioemotional development during research and prevention efforts of delinquent behavior.

Neural mechanisms of impulse control in sexually risky adolescents

The consequences of risky sexual behavior are of public concern. Adolescents contribute disproportionately to negative consequences of risky sexual behavior. However, no research has examined the neural correlates of impulse control and real-world engagement in risky sexual behavior in this population. The aim of the present study was to examine this question. Twenty sexually active adolescents performed an impulse control task during a functional magnetic resonance imaging (fMRI) scan and risky sexual behaviors were assessed through self-report. Sexual riskiness ratings were negatively associated with activation in the prefrontal cortex during response inhibition. These results suggest that diminished engagement of impulse control circuitry may contribute to sexual riskiness in adolescents.

Intact inhibitory control processes in abstinent drug abusers (II): a high-density electrical mapping study in former cocaine and heroin addicts

Response inhibition deficits are well-documented in drug users, and are related to the impulsive tendencies characteristic of the addictive phenotype. Addicts also show significant motivational issues that may accentuate these inhibitory deficits. We investigated the extent to which these inhibitory deficits are present in abstinence. Salience of the task stimuli was also manipulated on the premise that emotionally-valenced inputs might impact inhibitory efficacy by overcoming the blunted responses to everyday environmental inputs characteristic of this population. Participants performed response inhibition tasks consisting of both neutral and emotionally valenced stimuli while high-density event-related potentials (ERPs) were recorded. Electrophysiological responses (N2/P3 components) to successful inhibitions in abstinent abusers (N = 20) and non-using participants (N = 21) were compared. In contrast to previous work in current users, our abstinent cohort showed no detectable behavioral or electrophysiological differences in their inhibitory responses, and no differences on self-reports of impulsivity, despite their long histories of chronic use (mean = 10.3 years). The current findings are consistent with a recovery of inhibitory control processes as a function of abstinence. Abstinent former users, however, did show a reduced modulation, relative to controls, of their ERPs to valenced input while performing successful inhibitions, although contrary to our hypothesis, the use of valenced inputs had no impact on inhibitory performance. Reduced ERP modulation to emotionally valenced inputs may have implications for relapse in emotional contexts outside the treatment center.