Cognitive Performance by Humans During a Smoked Cocaine Binge-Abstinence Cycle

Sleep dysregulation in binge eating disorder and "food addiction": the orexin (hypocretin) system as a potential neurobiological link

It has been proposed that binge eating reflects a pathological compulsion driven by the "addictive" properties of foods. Proponents of this argument highlight the large degree of phenomenological and diagnostic overlap between binge eating disorder (BED) and substance use disorders (SUDs), including loss of control over how much is consumed and repeated unsuccessful attempts to abstain from consumption, as well as commonalities in brain structures involved in food and drug craving. To date, very little attention has been given to an additional behavioral symptom that BED shares with SUDs-sleep dysregulation-and the extent to which this may contribute to the pathophysiology of BED. Here, we review studies examining sleep outcomes in patients with BED, which collectively point to a heightened incidence of sleep abnormalities in BED. We identify the orexin (hypocretin) system as a potential neurobiological link between compulsive eating and sleep dysregulation in BED, and provide a comprehensive update on the evidence linking this system to these processes. Finally, drawing on evidence from the SUD literature indicating that the orexin system exhibits significant plasticity in response to drugs of abuse, we hypothesize that chronic palatable food consumption likewise increases orexin system activity, resulting in dysregulated sleep/wake patterns. Poor sleep, in turn, is predicted to exacerbate binge eating, contributing to a cycle of uncontrolled food consumption. By extension, we suggest that pharmacotherapies normalizing orexin signaling, which are currently being trialed for the treatment of SUDs, might also have utility in the clinical management of BED.

Empathy deficits and their behavioral, neuroanatomical, and functional connectivity correlates in smoked cocaine users

Reduced empathic abilities are frequently observed in drug abusers. These deficits may compromise interpersonal interactions and contribute to diminished social functioning. However, previous evidence regarding empathy and addiction is behaviorally unspecific and virtually null in terms of their brain structural or functional correlates. Moreover, no previous study has investigated how empathy is affected by drugs whose consumption is particularly characterized by counter-empathic behaviors. Here, we conducted the first assessment of neurocognitive correlates of empathy for pain in dependent users (predominantly men) of smoked cocaine (SC, coca paste, n = 37). We compared their performance in the empathy task with that of two groups matched in relevant demographic variables: 24 dependent users of insufflated cocaine hydrochloride (CC) and 21 healthy controls. In addition, we explored the structural anatomy and functional connectivity (FC) correlates of empathic impairments across groups. Our results showed that, compared to CC and controls, SC users exhibited a selective reduction of empathic concern for intentional harms. These impairments were associated with lower gray matter volumes in regions subserving social cognition (i.e., right inferior parietal lobule, supramarginal and angular gyri). Furthermore, reduced empathic concern correlated with FC within affective empathy and social cognition networks, which are also linked to cognitive changes reported in addiction (i.e., inferior frontal and orbital gyri, posterior insula, supplementary motor area, cingulate cortex). Our findings suggest that chronic consumption of SC may involve reduced empathic concern and relevant neuroanatomical and FC abnormalities, which, in turn, may result in social interaction dysfunction. These results can inform theoretical and applied developments in neuropsychopharmacology.

Increased self-reported impulsivity in methamphetamine users maintaining drug abstinence

BACKGROUND

Impulsivity has been proposed as an important factor in the initiation and maintenance of addiction. Indirect evidence suggests that some methamphetamine users report less impulsivity when they are using methamphetamine compared to when abstaining from drug use, but this hypothesis has not been directly tested.

OBJECTIVES/METHODS

In this study, self-reports of impulsivity were obtained from 32 methamphetamine-dependent (DSM-IV) research participants and 41 healthy control subjects, using the Barratt Impulsiveness Scale-11. The methamphetamine users were assessed during an active period of methamphetamine use, as determined through urinalysis, and again after approximately 1 week of confirmed abstinence. Control subjects likewise completed two assessments. A subset of participants also completed serial assessments of the Beck Depression Inventory (Methamphetamine Group, N = 17, Control Group, N = 38) and the Methamphetamine Withdrawal Questionnaire (Methamphetamine Group, N = 12).

RESULTS

There was a significant interaction of group with time on impulsivity (p = 0.044), reflecting a significant increase from the first to the second assessment in the methamphetamine users (p = 0.013), but no change among healthy control subjects. In contrast, depressive and withdrawal symptoms significantly decreased between the first and second assessments in the methamphetamine users (ps ≤0.01). Change in impulsivity in methamphetamine users was not significantly correlated with change in withdrawal or depression (ps >0.05).

CONCLUSIONS

These findings suggest that methamphetamine users report more impulsivity when abstaining from drug use, an effect that is not significantly related to methamphetamine withdrawal. Attenuation of impulsivity may reinforce continued methamphetamine use in these individuals.

Working memory deficits and alterations of ERK and CREB phosphorylation following withdrawal from cocaine self-administration

BACKGROUND

The mechanisms underlying memory functions during withdrawal from the chronic drug use are poorly understood.

METHODS

We assessed learning and spatial working memory using the delayed alternation assay (T-maze) in rats, previously subjected to cocaine self-administration. The T-maze training was conducted 1-5 weeks after cocaine cessation; working memory efficacy was assessed at 5-8 weeks of drug withdrawal. After behavioral training and testing, the rats were sacrificed and the levels of p-CREB/CREB and p-ERK2/ERK2 in several brain areas were measured. The same molecular assessment was performed in rats with cocaine injections, but forced to drug abstinence in home cages.

RESULTS

After 5 weeks of cocaine withdrawal from self-administration, a significant impairment of working memory under increased working memory load (inter-trial delay extended to 30s), with no changes at baseline conditions (inter-trial delay 10s), was noticed. Neither acquisition phase nor working memory performance measured 6-8 weeks after the last drug intake differed between cocaine or saline pretreated rats. Upon T-maze training and 8-week withdrawal, cocaine-pretreated rats had higher levels of p-CREB/CREB in prefrontal cortex and dorsal striatum and lower in hippocampus compared to saline rats. Increased levels of p-ERK2/ERK2 were observed in dorsal striatum, hippocampus and decreased in nucleus accumbens. In cocaine-pretreated caged rats no changes in p-CREB/CREB levels were observed, while ERK2 levels either decreased (frontal cortex) or increased (nucleus accumbens).

CONCLUSION

Our results suggest that cocaine self-administration results in cognitive impairments and alterations in ERK/CREB signaling pathway long after discontinuation of drug use.

Executive dysfunction in chronic cocaine users: an exploratory study

INTRODUCTION

Chronic cocaine use is associated with some executive deficits. We assessed executive functions using ecologically valid tests in chronic cocaine users.

OBJECTIVES

To investigate the relationship between executive deficits and three measures of severity of cocaine use: years of use, quantity used, and frequency of use.

METHODS

Twenty-four cocaine users were compared with twenty-seven community controls. We used Student's t-test and Chi-squared to compare means and categorical variables, respectively. Linear regression analyses for the adjusted comparative analysis between cases and controls, and severity of cocaine use among cocaine users were performed.

RESULTS

Chronic cocaine users performed worse on measures of attention and working memory (Forward and Backward Digit Span, p<.001), set-shifting abilities (difference score between the Trail Making B and A, TMB-A, p=.006), cognitive test of mental flexibility and response inhibition (Rule Shift Cards) (p<.001), and prefrontal functioning (Wisconsin Card Sorting Test, WCST, p=.023) than controls. Years of cocaine use were associated with deficits in the Backward Digit Span (p=.041; CI 95%: -.760 to -.002), the TMB-A (p=.026; CI 95%: .687 to 9.761), the Zoo Map (p=.034; CI 95%: -.480 to -.021), and the Rule Shift Cards (p=.006; CI 95%: -.836 to -.164), among others. Quantity of cocaine use was associated with executive deficits measured by the Forward Digit Span (p=.007; CI 95%: -.727 to -.133), the TMB-A (p=.021; CI 95%: 5.304-57.945), and the number of perseverative errors in the WSCT (p=.002; CI 95%: -10.654 to -2.800). Frequency of cocaine was associated with deficits in the Backward Digit Span (p=.042; CI 95%: -1.548 to -.030).

CONCLUSIONS

Chronic use of cocaine is associated with executive deficits, which may influence patients' functionality, prognosis, and therapeutic failure.

Comparative neuroscience of stimulant-induced memory dysfunction: role for neurogenesis in the adult hippocampus

The discovery that the addictive drugs impair neurogenesis in the adult hippocampus has prompted the elaboration of new biological hypotheses to explain addiction and drug-induced cognitive dysfunction. Considerable evidence now implicates the process of adult neurogenesis in at least some critical components of hippocampal-dependent memory function. In experimental models, psychomotor stimulant drugs produce alterations in the rate of birth, survival, maturation and functional integration of adult-born hippocampal neurons. Thus some of the deleterious consequences of drug abuse on memory could result from the neurotoxic actions of drugs on adult hippocampal neurogenesis. In this review, we will first summarize preclinical and clinical literature on the disruptive effects of drugs such as cocaine and ecstasy in the areas of learning, memory and attention. We will also summarize data that document the widespread effects of stimulant drugs on progenitor activity and precursor incorporation in the adult dentate gyrus. Finally, we will examine evidence that supports the involvement of hippocampal neurogenesis in specific aspects of learning and memory function and we will consider critically the hypothesis that some of the negative consequences of drug abuse on cognition might be ascribed to deficits in adult hippocampal neurogenesis. Evidence suggests that stimulant abuse impacts negatively on at least four areas of memory/cognitive function that may be influenced by adult hippocampal neurogenesis: contextual memory, spatial memory, working memory and cognitive flexibility.

Using a novel alternative to drug choice in a human laboratory model of a cocaine binge: a game of chance

Human laboratory studies have shown that, once initiated, cocaine self-administration is difficult to disrupt using non-drug alternatives. This inpatient study examined whether binge self-administration of cocaine could be altered by an immediate, non-drug reinforcer. Ten cocaine-dependent participants completed 5 consecutive laboratory session days with 2 sessions per day (a model binge), 9 days where cocaine was not available, and subsequent 2 laboratory session days where cocaine was again available (a second model binge). In each laboratory session, participants could choose to either self-administer smoked cocaine or play a game of chance by drawing a pre-determined number of balls from a bingo wheel. Balls were worth monetary amounts from $0 to $20. Participants' choice to smoke cocaine varied as a function of number of balls drawn. Thus, this game of chance served as an alternative reinforcer to smoking cocaine. Choice varied lawfully as a function of the number of opportunities to earn money indicating that an immediate behavioral alternative can reduce cocaine self-administration after initiation of use. The current model could be used to evaluate whether behavioral and pharmacological manipulations shift choice from cocaine to a non-drug alternative.

Repeated dosing with oral cocaine in humans: assessment of direct effects, withdrawal, and pharmacokinetics

Cocaine withdrawal symptoms are thought to play a role in relapse; studies characterizing the symptomatology have yielded mixed findings. This study sought to examine the pharmacodynamic/pharmacokinetic profile of repeated high dose exposure to oral cocaine and characterize acute and protracted withdrawal in cocaine abusers. This study employed a repeated-dosing, single-blind design in which subjects (n = 9), resided for 40 days on a closed ward. They were maintained for two 4-day cocaine exposure periods (Days 1-4 & Days 9-12, cocaine 175 mg, p.o.; 5 hourly doses; 875 mg/day) separated by a 4-day matched placebo exposure period (Days 5-8). After these 12 days, an additional period of 28 days of placebo maintenance followed (Days 13-40). Test sessions were conducted during each phase; measures of mood, drug effects, sleep, pharmacokinetics, and prolactin were collected throughout the study. The dosing regimen produced cocaine plasma concentrations (Cmax of 680 ng/mL) two to threefold higher than typically seen in acute dose studies. Prototypic psychostimulant effects, including subjective ratings of euphoric effects (liking, high, good effects) and significant cardiopressor effects, were sustained during the active dosing periods, corresponding to the rise and fall of plasma cocaine. Withdrawal-like symptoms (i.e., disruptions of sleep, increased ratings of anxiety, irritability, crashing) were observed within 24-hr after cessation of dosing. Cocaine reduced prolactin acutely, but no sustained alterations were observed for this measure or for other signs or symptoms during the 28-day abstinence period. These findings indicate that exposure to controlled high doses of cocaine produces modest symptoms consistent with cocaine withdrawal within hours of cessation of dosing but provide no evidence of symptoms persisting beyond 24 hours.

Approaches to measuring the effects of wake-promoting drugs: a focus on cognitive function

OBJECTIVES

In clinical drug development, wakefulness and wake-promotion may be assessed by a large number of scales and questionnaires. Objective assessment of wakefulness is most commonly made using sleep latency/maintenance of wakefulness tests, polysomnography and/or behavioral measures. The purpose of the present review is to highlight the degree of overlap in the assessment of wakefulness and cognition, with consideration of assessment techniques and the underlying neurobiology of both concepts.

DESIGN

Reviews of four key areas were conducted: commonly used techniques in the assessment of wakefulness; neurobiology of sleep/wake and cognition; targets of wake promoting and/or cognition enhancing drugs; and ongoing clinical trials investigating wake promoting effects.

RESULTS

There is clear overlap between the assessment of wakefulness and cognition. There are common techniques which may be used to assess both concepts; aspects of the neurobiology of both concepts may be closely related; and wake-promoting drugs may have nootropic properties (and vice versa). Clinical trials of wake-promoting drugs often, though not routinely, assess aspects of cognition.

CONCLUSIONS

Routine and broad assessment of cognition in the development of wake-promoting drugs may reveal important nootropic effects, which are not secondary to alertness/wakefulness, whilst existing cognitive enhancers may have underexplored or unknown wake promoting properties.

Neuropsychological assessment of current and past crack cocaine users

BACKGROUND

Cognitive changes due to crack cocaine consumption remain unclear.

METHODS

For clarification, 55 subjects were assigned to three groups: control group, crack cocaine current users, and ex-users. Participants were submitted to Mini-Mental State Examination (MMSE) and tasks evaluating executive functioning and verbal memory. Mood state was also measured. Intergroup comparisons were carried out.

RESULTS

Control group performance on the MMSE was better than that of users and ex-users. Verbal memory performance for logical memory of users was impaired. Ex-users scored lower on DSST and Trail Making Test (Part B).

CONCLUSION

Chronic crack cocaine use seems to disrupt general cognitive functioning (MMSE), verbal memory, and attentional resources, but findings suggest that some of these effects could be reversed by abstinence.

Sleep architecture, cocaine and visual learning

BACKGROUND

Disturbances in sleep associated with chronic cocaine use may underlie abstinence-related cognitive dysfunction. We hypothesized that sleep-related cognitive function would be impaired in chronic cocaine users, and that this impairment would be associated with abstinence-related changes in sleep architecture.

METHODS

Twelve chronic cocaine users completed a 23-day in-patient study that included randomized, placebo-controlled, cocaine self-administration sessions. We report polysomnographic measurement of rapid eye-movement (REM) sleep and slow-wave activity, and performance on a visual texture discrimination task.

FINDINGS

Progressive abstinence from cocaine was associated with characteristic changes in REM sleep. REM sleep was shortest on nights following cocaine use and rebounded in the first week of abstinence before diminishing with progressive abstinence, following a pattern opposite that of slow-wave activity. Overnight visual learning was observed over the first night following 3 consecutive days of laboratory cocaine use; however, learning was not observed at 3 days or 17 days of abstinence. Across all points of abstinence, early-night slow-wave activity was associated strongly with non-deterioration of visual performance overnight. Furthermore, overnight enhancement of visual performance was predicted by the co-occurrence of sufficient early-night slow-wave activity and late night REM sleep, similar to results from studies in healthy subjects.

CONCLUSIONS

These results suggest that abstinence-associated sleep-dependent learning deficits are related to characteristic changes in sleep architecture, and promote the idea that treatments directed at sleep ('somno-tropic' treatments) could be helpful in offsetting physiological consequences of cocaine abstinence.

Effect of illicit recreational drugs upon sleep: cocaine, ecstasy and marijuana

The illicit recreational drugs cocaine, ecstasy and marijuana have pronounced effects upon sleep. Administration of cocaine increases wakefulness and suppresses REM sleep. Acute cocaine withdrawal is often associated with sleep disturbances and unpleasant dreams. Studies have revealed that polysomnographically assessed sleep parameters deteriorate even further during sustained abstinence, although patients report that sleep quality remains unchanged or improves. This deterioration of objective sleep measures is associated with a worsening in sleep-related cognitive performance. Like cocaine, 3,4-methylenedioxymethamphetamine (MDMA; "ecstasy") is a substance with arousing properties. Heavy MDMA consumption is often associated with persistent sleep disturbances. Polysomnography (PSG) studies have demonstrated altered sleep architecture in abstinent heavy MDMA users. Smoked marijuana and oral Delta-9-tetrahydrocannabinol (THC) reduce REM sleep. Moreover, acute administration of cannabis appears to facilitate falling asleep and to increase Stage 4 sleep. Difficulty sleeping and strange dreams are among the most consistently reported symptoms of acute and subacute cannabis withdrawal. Longer sleep onset latency, reduced slow wave sleep and a REM rebound can be observed. Prospective studies are needed in order to verify whether sleep disturbances during cocaine and cannabis withdrawal predict treatment outcome.

Differential effects of self-administered cocaine in adolescent and adult rats on stimulus-reward learning

RATIONALE

Adult cocaine addicts, abstinent at the time of testing, show a variety of neurocognitive impairments. Less clear is whether there are differences in the degree of impairment if cocaine use is initiated during adolescence rather than adulthood.

OBJECTIVES

Using a preclinical model, we evaluated if stimulus-reward learning was impacted differently in rats exposed to cocaine during adolescence (beginning on postnatal day 37) vs adulthood (beginning on postnatal days 74-79) and then tested after a drug-free period.

MATERIALS AND METHODS

A yoked-triad design of intravenous cocaine self-administration in adult (n = 8 triads) and adolescent (n = 8 triads) rats was used. Sets of three animals either contingently self-administered cocaine or received cocaine or saline in a noncontingent manner. Rats self-administering 1-mg/kg doses of cocaine responded under a fixed-ratio 5, timeout 20-s schedule of reinforcement. After 18 2-h drug or saline sessions, all rats (now adults) began the drug-free period in their home environments. Testing in a stimulus-reward learning task (conditioned cue preference) began 19 days later.

RESULTS

Self-administration behavior was similar in adolescent and adult rats. Lever responses were not significantly different, and both age groups averaged approximately 20 infusions per session. Rats contingently self-administering cocaine or passively exposed to cocaine during adulthood showed stimulus-reward learning deficits in the conditioned cue preference task. Rats exposed to contingent or noncontingent cocaine during adolescence had normal learning, showing strong preferences for a Froot Loops-paired cue.

CONCLUSIONS

These findings suggest that adolescents are insensitive to cocaine-induced impairment of learning related to amygdala memory system functioning.

Thalamo-cortical dysfunction in cocaine abusers: implications in attention and perception

Cocaine affects sensory perception and attention, but little is known about the neural substrates underlying these effects in the human brain. We used functional magnetic resonance imaging (fMRI) and a sustained visuospatial attention task to assess if the visual attention network is dysfunctional in cocaine abusers (n=14) compared to age-, gender-, and education-matched controls (n=14). Compared with controls, cocaine abusers showed (1) hypo-activation of the thalamus, which may reflect noradrenergic and/or dopaminergic deficits; (2) hyper-activation in occipital and prefrontal cortices, which may reflect increased visual cortical processing to compensate for inefficient visual thalamic processing; and (3) larger deactivation of parietal and frontal regions possibly to support the larger hemodynamic supply to the hyper-activated brain regions. These findings provide evidence of abnormalities in thalamo-cortical responses in cocaine abusers that are likely to contribute to the impairments in sensory processing and in attention. The development of therapies that diminish these thalamo-cortical deficits could improve the treatment of cocaine addiction.

Widespread disruption in brain activation patterns to a working memory task during cocaine abstinence

Cocaine abstinence is associated with impaired performance in cognitive functions including attention, vigilance and executive function. Here we test the hypothesis that cognitive dysfunction during cocaine abstinence reflects in part impairment of cortical and subcortical regions modulated by dopamine. We used functional magnetic resonance imaging (fMRI) to study brain activation to a verbal working memory task in cocaine abusers (n=16) and healthy controls (n=16). Compared to controls, cocaine abusers showed: (1) hypoactivation in the mesencephalon, where dopamine neurons are located, as well as the thalamus, a brain region involved in arousal; (2) larger deactivation in dopamine projection regions (putamen, anterior cingulate, parahippocampal gyrus, and amygdala); and (3) hyperactivation in cortical regions involved with attention (prefrontal and parietal cortices), which probably reflects increased attention and control processes as compensatory mechanisms. Furthermore, the working memory load activation was lower in the prefrontal and parietal cortices in cocaine abusers when compared with controls, which might reflect limited network capacity. These abnormalities were accentuated in the cocaine abusers with positive urines for cocaine at time of study (as compared to cocaine abusers with negative urines) suggesting that the deficits may reflect in part early cocaine abstinence. These findings provide evidence of impaired function of regions involved with executive control, attention and vigilance in cocaine abusers. This widespread neurofunctional disruption is likely to underlie the cognitive deficits during early cocaine abstinence and to reflect involvement of dopamine as well as other neurotransmitters.

Sleep, sleep-dependent procedural learning and vigilance in chronic cocaine users: Evidence for occult insomnia

Sleep disturbance has been implicated in cocaine use; however, the nature of the disturbance and its potential effects on cognition and learning are largely unknown. Twelve chronic cocaine users completed a 23-day inpatient study that included randomized, placebo-controlled, cocaine self-administration sessions. Six subjects received cocaine on each of days 4-6 and placebo on days 18-20, the other six received cocaine on each of days 18-20 and placebo on days 4-6. Sleep was measured by polysomnography, the Nightcap sleep monitor, and self-reported measures. Simple and vigilance reaction times were measured daily; a motor-sequence test of procedural learning was administered four times. Electrophysiological measures of sleep showed a different pattern than self-reported sleep across cocaine administration and abstinence: total sleep time and sleep latency were at their worst by 14-17 days of abstinence while self-reported sleep was at its best. Vigilance correlated positively with electrophysiologically measured sleep and negatively with self-reported measures. Similarly, sleep-dependent procedural learning correlated with total sleep time and was impaired at 17 days abstinence relative to 2- and 3-days abstinence. Slow-wave activity was lowest at days 4-9 of abstinence and highest during use and days 10-17 of abstinence. With sustained abstinence, chronic cocaine users exhibit decreased sleep, impaired vigilance and sleep-dependent procedural learning, and spectral activity suggestive of chronic insomnia. However, they report subjectively improving sleep, indicating they are unaware of this "occult" insomnia. These results suggest the possibility of homeostatic sleep drive dysregulation in chronic cocaine users.