Elevated Impulsivity Research Articles

Elevated Impulsivity and Impaired Decision-Making in Abstinent Ecstasy (MDMA) Users Compared to Polydrug and Drug-Naïve Controls

Ecstasy (MDMA; 3,4-methylenedioxymethamphetamine) has a well-recognized neurotoxic effect on central serotonergic (5-HT) systems in animals, and there is some evidence of persistent serotonergic dysregulation in human ecstasy users. Serotonin is believed to mediate impulsive behavior and effective decision-making. Thus, the aim of the present study was to investigate impulsive behavior and decision-making in abstinent regular ecstasy users. Three groups were compared: 'ecstasy users' (recreational ecstasy users who reported modest use of illicit drugs other than cannabis), 'polydrug controls' (ecstasy naïve illicit drug users), and 'drug-naïve controls'. All participants completed personal details and general drug history questionnaires, the National Adult Reading Test, Matching Familiar Figures Test (MFF20), a risky decision-making task (RDMT), and the Card Arranging Reward Responsivity Objective Test (CARROT). The groups did not differ on the CARROT measure of responsiveness to financial incentive; however, the ecstasy group displayed significantly elevated MFF20 impulsivity, and showed reduced discrimination between magnitudes of prospective gains and losses when making risky decisions, compared to the 'polydrug' and 'drug-naïve' control groups. These findings may reflect a vulnerability of 5-HT systems in the orbital prefrontal cortex and interconnected corticolimbic circuitry to the cumulative neurotoxic effects of ecstasy and have clinical significance for regular ecstasy users. The combination of elevated impulsivity and impaired use of reinforcement cues in uncertain decision-making may comprise risk factors for continued drug abuse and everyday functioning.

Measuring Impulsivity and Modeling Its Association With Cigarette Smoking

Two types of behavioral measure are primarily used to examine impulsivity in humans and animals: Go/No-go tasks to assess inhibition and relative preference tasks to assess delay aversion. Several examples of each type of task are described so that common cognitive processes and variables affecting performance can be identified. Data suggest that smokers are more impulsive on each of these impulsivity measures than nonsmokers. Several models can be proposed to account for this group difference: (a) the differences predate and, possibly, are causally related to the initiation of cigarette smoking; (b) higher levels of impulsivity are associated with continued smoking, either through an association with heightened positive subjective effects of nicotine or heightened negative effects of nicotine abstinence (withdrawal); (c) nicotine causes neuroadaptations that result in elevated impulsivity in smokers. Studies relating to each of these models are reviewed, and it is concluded that all three models may contribute to the observed higher levels of impulsivity in smokers. However, pertinent studies are limited and additional systematic research is needed.

Impulsivity in abstinent alcohol-dependent patients: relation to control subjects and type 1–/type 2–like traits

Extensive literature has linked behavior control problems in childhood to risk for alcoholism, but impulsivity in alcohol-dependent adults has not been well characterized. Using a variety of laboratory measures of impulsivity, we assessed whether detoxified alcohol-dependent patients [(ADP); n = 130] were more impulsive than control subjects [(CS); n = 41]. In comparison with CS, ADP demonstrated (1) increased rates of commission errors, but not omission errors, in a continuous performance test, (2) a more severe devaluation of delayed reward, (3) increased rates of risky responses in a new risk-taking paradigm, and (4) higher psychometric scores of impulsivity and aggression. Across all subjects, aggressiveness correlated significantly with severity of delay discounting. A post hoc analysis of data obtained for male ADP indicated that, in comparison with patients with late onset of problem drinking and no problem-drinking parent, those ADP with earlier age of problem drinking and who reported a problem-drinking father (type 2–like alcohol dependence) demonstrated faster response latencies and more responses to non-target stimuli (commission errors) in the continuous performance test, as well as higher psychometric aggression. In contrast, these subtypes of male ADP did not differ in delay discounting and risk taking. These findings collectively indicate that, in comparison with CS, ADP are more impulsive in several dimensions, with elevated impulsivity in a working memory task as well as aggressivity characteristic of alcohol-dependent men with type 2–like features.

Impulsivity in smoking, nonsmoking, and ex-smoking alcoholics

The impulsivity levels were evaluated and compared in smoking, nonsmoking, and ex-smoking abstinent alcoholics ( N=400) in a French alcohol detoxification center. Impulsivity was measured using the Barratt Impulsiveness Scale, French version (BIS 10). The BIS scores correlated inversely with age. Gender had no effect on impulsivity scores, while impulsivity was associated with smoking. Adding age as a covariate, however, eliminated or moderated the association, with three exceptions: (1) among males, heavy smokers were more impulsive than nonsmokers and medium smokers; (2) on the nonplanning subscale, heavy smokers were more impulsive than all other groups, and (3) current smokers were more impulsive than ex-smokers. Elevated impulsivity levels appear to be an obstacle to smoking cessation. In addition, stopping smoking may diminish impulsivity levels in alcoholics. Routine testing of impulsivity in current alcoholic smokers might predict who might successfully become an ex-smoker.

Adolescent exposure to methylphenidate alters the activity of rat midbrain dopamine neurons

BackgroundMethylphenidate is commonly used to treat children and adolescents with attention-deficit/hyperactivity disorder. A health concern is its long-term effects with respect to later stimulant exposure. We reported that repeated exposure to a low dose of methylphenidate during adolescence increases self-administration of a low, typically nonreinforcing dose of cocaine in adult rats. We also showed that enhanced vulnerability to cocaine is associated with elevated impulse and bursting activity of midbrain dopamine neurons in drug-naïve adult rats and might constitute a substrate critically associated with abuse liability. Thus we sought to determine whether repeated exposure to low-dose methylphenidate in adolescence alters dopamine neuronal excitability in adulthood. MethodsAfter 3-day and 2-week withdrawal from repeated low-dose adolescent exposure to methylphenidate, we used extracellular single-unit recording in chloral hydrate–anesthetized rats to determine basal firing and bursting activity of midbrain dopamine neurons and dopamine autoreceptor sensitivity to the D2-class direct receptor agonist quinpirole. ResultsDopamine neuronal impulse activity was increased after 3 days and decreased after 2 weeks' withdrawal from methylphenidate given in adolescence. No difference between groups was evident with respect to autoreceptor sensitivity to quinpirole. ConclusionsAdolescent exposure to methylphenidate induces neuronal changes associated with increased addiction liability in rats.

Elevated levels of impulsivity and reduced place conditioning with d-amphetamine: two behavioral features of adolescence in mice.

Human adolescents may have experience with easily available psychoactive drugs. Impulsivity and/or peculiarities in reward systems may play a role. These variables were studied in adolescent (Postnatal Day [PND] 30-49) and adult (PND > 60) CD-1 mice. In Experiment 1 (impulsivity), food-restricted mice were tested in operant chambers with 2 nose-poking holes that delivered 1 food pellet immediately or 5 pellets after a delay, respectively. Delay length was increased over days (0-100 s). Adolescent mice showed a shift to the left in the intolerance-delay curve, as well as enhanced demanding when nose-poking was not reinforced. In Experiment 2 (place conditioning with d-amphetamine at 0.0. 1.0, 2.0, 3.3, or 5.0 mg/kg for 3 days), adolescent mice showed no reliable evidence of place conditioning when compared with adults. Hence, 2 main features of adolescence were elevated impulsivity and restlessness, and low (or absent) rewarding efficacy of amphetamine.

Increased impulsivity in cocaine dependent subjects independent of antisocial personality disorder and aggression

Several previous studies show a relationship between impulsivity and substance abuse; however, it is unclear whether the increased impulsivity seen in substance dependent groups is specifically related to substance abuse, or if it is due to concomitant antisocial personality disorder (ASPD) or aggression. The issue of whether impulsivity is specifically related to substance abuse is important since it has a bearing on risk factors for development of substance abuse. To determine whether cocaine dependent subjects show increased impulsivity independent of ASPD, the Barratt impulsiveness scale (BIS-11), a delayed reward laboratory measure of impulsivity, and the life history of aggression scale were administered to 49 cocaine dependent subjects and 25 controls. Results showed that cocaine dependent subjects with ASPD were more impulsive and aggressive than controls, but cocaine dependent subjects without ASPD were also more impulsive compared to controls. Controlling for aggression history, cocaine dependent subjects without ASPD continued to have elevated impulsivity as measured by the BIS-11, but not the delayed reward task. This study supports the hypothesis that the increased impulsivity as measured by the BIS-11 in cocaine dependent individuals is not exclusively due to concomitant increases in aggression or ASPD.

Long-Term Neuropsychiatric Consequences of "Ecstasy" (MDMA): A Review

The recreational drug "ecstasy" (3,4-methylenedioxymethamphetamine, or MDMA) is widely used by young people throughout the world. Experimental studies indicate that MDMA damages serotonergic neurons in animals and possibly in humans. Repeated use may induce long-term neurotoxic effects, with cognitive and behavioral implications. We reviewed both the preclinical and the clinical literature to assess the evidence for persistent neuropsychiatric sequelae in humans. We focused on studies of chronic recreational use and reports of presence or absence of neurological, psychiatric, and psychological problems related to MDMA exposure. These investigations show repeated use of ecstasy to be associated with sleep, mood, and anxiety disturbances, elevated impulsiveness, memory deficits, and attention problems, which may persist for up to 2 years after cessation. In a subset of humans, particularly adolescents, depletion of serotonin by MDMA use may hasten or enhance vulnerability to a wide array of neuropsychiatric problems. Together, the studies reviewed provide substantial evidence that MDMA causes neuronal damage in animals and humans. Additional research is necessary to determine whether the MDMA-induced destruction of serotonergic neurons can have long-term and possibly permanent neuropsychiatric consequences in humans.

Enhanced Vulnerability to Cocaine Self-Administration Is Associated with Elevated Impulse Activity of Midbrain Dopamine Neurons

Individual differences in responding to a novel environment predict behavioral and neurochemical responses to psychostimulant drugs. Rats with a high locomotor response to a novel environment (HRs) exhibit enhanced self-administration (SA) behavior, sensitization, and basal or drug-induced dopamine release in the nucleus accumbens compared with rats with a low response to the novel context (LRs). In this study, we determined whether such differences in vulnerability to drug addiction might be related to differences in dopamine (DA) neuron activity. Rats were divided into HRs and LRs according to their response to a novel environment and then tested for acquisition of cocaine SA. HRs rapidly acquired cocaine SA (175 microg/kg per infusion), whereas LRs did not. Differences in cocaine SA were not caused by differences in exploratory behavior or sampling because these behaviors did not differ in HRs and LRs self-administering a saline solution. In a separate experiment, we used extracellular single-unit recordings and found that HRs exhibit higher basal firing rates and bursting activity of DA neurons in the ventral tegmental area and, to a lesser extent, in the substantia nigra pars compacta. The greater activity of midbrain DA cells in HRs was accompanied by reduced sensitivity to the inhibitory effects of a DA D2-class receptor agonist, indicating possible subsensitivity of impulse-regulating DA autoreceptors. These results demonstrate that differences in the basal activity of DA neurons may be critically involved in determining individual vulnerability to drugs of abuse.