Molecular and circuit mechanisms regulating cocaine memory

Risk of relapse is a major challenge in the treatment of substance use disorders. Several types of learning and memory mechanisms are involved in substance use and have implications for relapse. Associative memories form between the effects of drugs and the surrounding environmental stimuli, and exposure to these stimuli during abstinence causes stress and triggers drug craving, which can lead to relapse. Understanding the neural underpinnings of how these associations are formed and maintained will inform future advances in treatment practices. A large body of research has expanded our knowledge of how associative memories are acquired and consolidated, how they are updated through reactivation and reconsolidation, and how competing extinction memories are formed. This review will focus on the vast literature examining the mechanisms of cocaine Pavlovian associative memories with an emphasis on the molecular memory mechanisms and circuits involved in the consolidation, reconsolidation, and extinction of these memories. Additional research elucidating the specific signaling pathways, mechanisms of synaptic plasticity, and epigenetic regulation of gene expression in the circuits involved in associative learning will reveal more distinctions between consolidation, reconsolidation, and extinction learning that can be applied to the treatment of substance use disorders.

Cocaine'omics: Genome-wide and transcriptome-wide analyses provide biological insight into cocaine use and dependence

We investigated the genetic and molecular architecture of cocaine dependence (CD) and cocaine use by integrating genome-/transcriptome-wide analyses. To prioritize candidates for follow-up investigation, we also sought to translate gene expression findings across species. Using data from the largest genome-wide association study (GWAS) of CD to date (n = 3176, 74% with CD), we assessed genomic heritability, gene-based associations, and tissue enrichment. We detected a significant single-nucleotide polymorphism heritability of 28% for CD and identified three genes (two loci) underlying this predisposition: the C1qL2 (complement component C1 q like 2), KCTD20 (potassium channel tetramerization domain containing 20), and STK38 (serine/threonine kinase 38) genes. Tissue enrichment analyses indicated robust enrichment in numerous brain regions, including the hippocampus. We used postmortem human hippocampal RNA-sequencing data from previous study (n = 15, seven chronic cocaine users) to follow up genome-wide results and to identify differentially expressed genes/transcripts and gene networks underlying cocaine use. Cross-species analyses utilized hippocampal gene expression from a mouse model of cocaine use. Differentially expressed genes/transcripts in humans were enriched for the genes nominally associated with CD via GWAS (P < 0.05) and for differentially expressed genes in the hippocampus of cocaine-exposed mice. We identified KCTD20 as a central component of a hippocampal gene network strongly associated with human cocaine use, and this gene network was conserved in the mouse hippocampus. We outline a framework to map and translate genome-wide findings onto tissue-specific gene expression, which provided biological insight into cocaine use/dependence.

Cocaine Directly Impairs Memory Extinction and Alters Brain DNA Methylation Dynamics in Honey Bees

Drug addiction is a chronic relapsing behavioral disorder. The high relapse rate has often been attributed to the perseverance of drug-associated memories due to high incentive salience of stimuli learnt under the influence of drugs. Drug addiction has also been interpreted as a memory disorder since drug associated memories are unusually enduring and some drugs, such as cocaine, interfere with neuroepigenetic machinery known to be involved in memory processing. Here we used the honey bee (an established invertebrate model for epigenomics and behavioral studies) to examine whether or not cocaine affects memory processing independently of its effect on incentive salience. Using the proboscis extension reflex training paradigm we found that cocaine strongly impairs consolidation of extinction memory. Based on correlation between the observed effect of cocaine on learning and expression of epigenetic processes, we propose that cocaine interferes with memory processing independently of incentive salience by directly altering DNA methylation dynamics. Our findings emphasize the impact of cocaine on memory systems, with relevance for understanding how cocaine can have such an enduring impact on behavior.

Neuropsychological comparisons of cocaine versus methamphetamine users: A research synthesis and meta-analysis

BACKGROUND

Previous meta-analytical research examining cocaine and methamphetamine separately suggests potentially different neuropsychological profiles associated with each drug. In addition, neuroimaging studies point to distinct structural changes that might underlie differences in neuropsychological functioning.

OBJECTIVES

This meta-analysis compared the effect sizes identified in cocaine versus methamphetamine studies across 15 neuropsychological domains.

METHOD

Investigators searched and coded the literature examining the neuropsychological deficits associated with a history of either cocaine or methamphetamine use. A total of 54 cocaine and 41 methamphetamine studies were selected, yielding sample sizes of 1,718 and 1,297, respectively. Moderator analyses were conducted to compare the two drugs across each cognitive domain.

RESULTS

Data revealed significant differences between the two drugs. Specifically, studies of cocaine showed significantly larger effect-size estimates (i.e., poorer performance) in verbal working memory when compared to methamphetamine. Further, when compared to cocaine, methamphetamine studies demonstrated significantly larger effect sizes in delayed contextual verbal memory and delayed visual memory.

CONCLUSION

Overall, cocaine and methamphetamine users share similar neuropsychological profiles. However, cocaine appears to be more associated with working memory impairments, which are typically frontally mediated, while methamphetamine appears to be more associated with memory impairments that are linked with temporal and parietal lobe dysfunction.

Prevalence of driving under the influence of psychoactive substances and road traffic crashes among Brazilian crack-using drivers

BACKGROUND

Substance use disorders are associated with the increased risk of driving under the influence (DUI), but little is known about crack-cocaine and its relationship with road traffic crashes (RTC).

METHOD

A multicenter sample of 765 crack-cocaine users was recruited in six Brazilian capitals in order to estimate the prevalence of DUI and RTC involvement. Legal, psychiatric, and drug-use aspects related with traffic safety were evaluated using the Addiction Severity Index - 6th version (ASI-6) and the Mini International Neuropsychiatric Interview.

RESULTS

Seventy-six (28.3%) current drivers reported accident involvement following crack-cocaine use. Among drivers (n=269), 45.7% and 30.5% reported DUIs in the past 6 months and 30 days, respectively. Drivers reporting DUI's in the past month (n=82) had higher scores in the "psychiatric", "legal", and "family problems" subscales from the ASI-6, and lower scores in the "family social support" subscale in comparison to those without a history of DUIs (n=187). An overall high prevalence of psychiatric comorbidity and substance consumption was observed. Participants with 5+ years of crack-cocaine use were more likely to have been in a RTC (RR=1.52, 95%IC: 1.02-2.75), independently of marijuana use, binge drinking and psychiatric comorbidities.

CONCLUSION

The high prevalence of RTC and DUI involvement among crack-using drivers supports the idea that they are at a high risk group regarding traffic safety. Years of crack consumption seem to be associated with RTC involvement. Also, the presence of psychiatric comorbidities, poly-drug use, and cognitive impairment usually associated with crack addiction could yield additional risk of accidents.

Transactivation of TrkB by Sigma-1 receptor mediates cocaine-induced changes in dendritic spine density and morphology in hippocampal and cortical neurons

Cocaine is a highly addictive narcotic associated with dendritic spine plasticity in the striatum. However, it remains elusive whether cocaine modifies spines in a cell type-specific or region-specific manner or whether it alters different types of synapses in the brain. In addition, there is a paucity of data on the regulatory mechanism(s) involved in cocaine-induced modification of spine density. In the current study, we report that cocaine exposure differentially alters spine density, spine morphology, and the types of synapses in hippocampal and cortical neurons. Cocaine exposure in the hippocampus resulted in increased spine density, but had no significant effect on cortical neurons. Although cocaine exposure altered spine morphology in both cell types, the patterns of spine morphology were distinct for each cell type. Furthermore, we observed that cocaine selectively affects the density of excitatory synapses. Intriguingly, in hippocampal neurons cocaine-mediated effects on spine density and morphology involved sigma-1 receptor (Sig-1 R) and its downstream TrkB signaling, which were not the case in cortical neurons. Furthermore, pharmacological inhibition of Sig-1 R prevented cocaine-induced TrkB activation in hippocampal neurons. Our findings reveal a novel mechanism by which cocaine induces selective changes in spine morphology, spine density, and synapse formation, and could provide insights into the cellular basis for the cognitive impairment observed in cocaine addicts.

Effects of drugs of abuse on hippocampal plasticity and hippocampus-dependent learning and memory: contributions to development and maintenance of addiction

It has long been hypothesized that conditioning mechanisms play major roles in addiction. Specifically, the associations between rewarding properties of drugs of abuse and the drug context can contribute to future use and facilitate the transition from initial drug use into drug dependency. On the other hand, the self-medication hypothesis of drug abuse suggests that negative consequences of drug withdrawal result in relapse to drug use as an attempt to alleviate the negative symptoms. In this review, we explored these hypotheses and the involvement of the hippocampus in the development and maintenance of addiction to widely abused drugs such as cocaine, amphetamine, nicotine, alcohol, opiates, and cannabis. Studies suggest that initial exposure to stimulants (i.e., cocaine, nicotine, and amphetamine) and alcohol may enhance hippocampal function and, therefore, the formation of augmented drug-context associations that contribute to the development of addiction. In line with the self-medication hypothesis, withdrawal from stimulants, ethanol, and cannabis results in hippocampus-dependent learning and memory deficits, which suggest that an attempt to alleviate these deficits may contribute to relapse to drug use and maintenance of addiction. Interestingly, opiate withdrawal leads to enhancement of hippocampus-dependent learning and memory. Given that a conditioned aversion to drug context develops during opiate withdrawal, the cognitive enhancement in this case may result in the formation of an augmented association between withdrawal-induced aversion and withdrawal context. Therefore, individuals with opiate addiction may return to opiate use to avoid aversive symptoms triggered by the withdrawal context. Overall, the systematic examination of the role of the hippocampus in drug addiction may help to formulate a better understanding of addiction and underlying neural substrates.

Neurodevelopmental Precursors and Consequences of Substance Use during Adolescence: Promises and Pitfalls of Longitudinal Neuroimaging Strategies

Neurocognitive and emotional regulatory deficits in substance users are often attributed to misuse; however most studies do not include a substance-naïve baseline to justify that conclusion. The etiological literature suggests that pre-existing deficits may contribute to the onset and escalation of use that are then exacerbated by subsequent use. To address this, there is burgeoning interest in conducting prospective, longitudinal neuroimaging studies to isolate neurodevelopmental precursors and consequences of adolescent substance misuse, as reflected in recent initiatives such as the NIH-led Adolescent Brain Cognitive Development (ABCD) study and the National Consortium on Alcohol and Neurodevelopment (NCANDA). To distinguish neurodevelopmental precursors from the consequences of adolescent substance use specifically, prospective, longitudinal neuroimaging studies with substance-naïve pre-adolescents are needed. The exemplar described in this article—i.e., the ongoing Adolescent Development Study (ADS)—used a targeted recruitment strategy to bolster the numbers of pre-adolescent individuals who were at increased risk of substance use (i.e., “high-risk”) in a sample that was relatively small for longitudinal studies of similar phenomena, but historically large for neuroimaging (i.e., N = 135; 11–13 years of age). At baseline participants underwent MRI testing and a large complement of cognitive and behavioral assessments along with genetics, stress physiology and interviews. The study methods include repeating these measures at three time points (i.e., baseline/Wave 1, Wave 2 and Wave 3), 18 months apart. In this article, rather than outlining specific study outcomes, we describe the breadth of the numerous complexities and challenges involved in conducting this type of prospective, longitudinal neuroimaging study and “lessons learned” for subsequent efforts are discussed. While these types of large longitudinal neuroimaging studies present a number of logistical and scientific challenges, the wealth of information obtained about the precursors and consequences of adolescent substance use provides unique insights into the neurobiological bases for adolescent substance use that will lay the groundwork for targeted interventions.

Cognitive functioning associated with stimulant use in patients with non-affective psychosis, their unaffected siblings and healthy controls

BACKGROUND

Little is known about the effect of stimulant use (amphetamines, cocaine, ecstasy) on cognitive functioning in schizophrenia patients. The current study examined (1) whether recency and frequency of stimulant use is associated with cognitive functioning and (2) whether these associations differ between psychotic patients, their unaffected siblings and controls.

METHOD

Participants completed a comprehensive cognitive test battery. Stimulant use was assessed by urinalysis and by the Composite International Diagnostic Interview (CIDI). Using random effects regression models, the main effects of Stimulant Use and the interaction with Diagnostic Status on cognitive functioning were assessed.

RESULTS

The interaction term between Stimulant Use and Diagnostic Status was not significant for any of the cognitive outcome variables, indicating similar effects of stimulant use in all three groups. Recent stimulant users showed more errors deficit in verbal learning in comparison to never users (Cohen's d = -0.60, p < 0.005). Lifetime frequent stimulant use was significantly associated with worse immediate and delayed verbal recall, working memory and acquired knowledge (Cohen's d = -0.22 to -0.29, p < 0.005). Lifetime infrequent stimulant use was not associated with significant cognitive alterations in comparison to never use.

CONCLUSIONS

The presence of cognitive deficits associated with lifetime stimulant use is dependent on the frequency of use, with no observed deficits in infrequent users and modest negative effects in frequent users.

Neurocognitive functioning of individuals with schizophrenia: using and not using drugs

OBJECTIVES

Research on neurocognition in schizophrenia, using modest samples and self-rated assessments, reports drug use contributes to improved rather than impaired cognitive function. We have sought to replicate these findings in a large sample of patients that had their drug-use status confirmed by laboratory assays and evaluated the potential differences in cognitive function between patients with positive and negative results.

METHODS

Nine hundred and seventy four schizophrenia patients completed neuropsychological and laboratory tests at screening/baseline of the Clinical Antipsychotic Trials of Intervention Effectiveness study. Radioimmunoassay (RIA) of hair tested for cannabis, cocaine and methamphetamine.

RESULTS

Many patients screened positive for drug use (n = 262; 27%), and there were no differences between patients with positive and negative results in terms of cognitive function after adjusting for multiple inference testing, except patients with positive RIA for methamphetamine demonstrated increased processing speed (corrected, P = .024). Moderator models were employed to explore potential subgroup differences in this pattern of results. At low medication dosages, patients with positive RIA for cocaine demonstrated decreased processing speed compared with patients with negative RIA for cocaine (uncorrected, P = .008). And for any other drugs with low psychopathology, patients with positive RIA demonstrated decreased working memory compared with patients with negative RIA (uncorrected, P = .006).

CONCLUSIONS

No positive effects of cannabis on cognitive function were observed, and drug use was not associated with improved neurocognition across most of the subgroup characteristics explored in this sample of schizophrenia patients.

Influence of the dopaminergic system, CREB, and transcription factor-κB on cocaine neurotoxicity

Cocaine is a widely used drug and its abuse is associated with physical, psychiatric and social problems. Abnormalities in newborns have been demonstrated to be due to the toxic effects of cocaine during fetal development. The mechanism by which cocaine causes neurological damage is complex and involves interactions of the drug with several neurotransmitter systems, such as the increase of extracellular levels of dopamine and free radicals, and modulation of transcription factors. The aim of this review was to evaluate the importance of the dopaminergic system and the participation of inflammatory signaling in cocaine neurotoxicity. Our study showed that cocaine activates the transcription factors NF-κB and CREB, which regulate genes involved in cellular death. GBR 12909 (an inhibitor of dopamine reuptake), lidocaine (a local anesthetic), and dopamine did not activate NF-κB in the same way as cocaine. However, the attenuation of NF-κB activity after the pretreatment of the cells with SCH 23390, a D1 receptor antagonist, suggests that the activation of NF-κB by cocaine is, at least partially, due to activation of D1 receptors. NF-κB seems to have a protective role in these cells because its inhibition increased cellular death caused by cocaine. The increase in BDNF (brain-derived neurotrophic factor) mRNA can also be related to the protective role of both CREB and NF-κB transcription factors. An understanding of the mechanisms by which cocaine induces cell death in the brain will contribute to the development of new therapies for drug abusers, which can help to slow down the progress of degenerative processes.

Concurrent use of khat and tobacco is associated with verbal learning and delayed recall deficits

AIMS

The present study assessed whether cigarette smokers who are also regular khat users would demonstrate greater impairments in verbal learning and recall compared to both non-smokers who are khat users and control subjects.

DESIGN

An independent-measures, between-subjects design with two covariates.

SETTING

An out-patient, university research center in Taiz, Yemen.

PARTICIPANTS

Subjects were 175 Yemeni college students (90 men, 85 women) ranging in age from 18 to 38 years. Seventy-five subjects were self-reported chronic cigarette smokers and khat users, 48 non-smoking subjects were self-reported to be chronic khat users and 52 non-smoking subjects reported no current use or history of khat use.

MEASUREMENTS

Verbal learning and verbal memory recall was assessed by subject performance on the Arabic version of the Rey Auditory Verbal Learning Test (RAVLT).

FINDINGS

Statistically significant differences (P < 0.05) were observed in RAVLT acquisition learning trials 2-5 and on delayed recall measures between concurrent khat and cigarette users compared to both the khat-only group and the control group of non-users of khat and cigarettes. On each of these trials, concurrent users recalled fewer words, demonstrating a slowed rate of verbal learning. This same pattern of performance was also seen on delayed recall measures. Khat use alone did not affect immediate or delayed recall of previously learned words.

CONCLUSIONS

Khat users who smoke cigarettes have a lower rate of verbal learning and delayed recall of previously learned verbal material than khat users who do not smoke cigarettes. This may be due to pre-existing differences between these groups of subjects.

Effects of acute and chronic cocaine administration on titrating-delay matching-to-sample performance

The effects of cocaine were examined under a titrating-delay matching-to-sample procedure. In this procedure, the delay between sample stimulus offset and comparison stimuli onset adjusts as a function of the subject's performance. Specifically, matches increase the delay and mismatches decrease the delay. Titrated delay values served as the primary dependent measure. After establishing stable performance in pigeons, several behaviorally-effective doses of cocaine were administered acutely. Dose-related within-session decreases in titrated delay values were observed. Following acute determinations, the dose of cocaine that produced the most rapid decline without eliminating performance was administered prior to each daily session. Chronic administration resulted in performance trending toward control levels. A redetermination of the dose-response function following chronic exposure revealed reduced potency (i.e., tolerance) under cocaine on titrated delay matching-to-sample performance. Supplemental analyses suggest that cocaine may serve as a disruptor of the stimulus conditions in which the performance was established.

Nicotine effects on immediate and delayed verbal memory after substance use detoxification

Decrements in verbal memory are commonly reported by detoxified treatment-seeking individuals. Although acute nicotine has been shown to improve attentional performance, its effects on verbal memory in substance abusers have not been addressed. Treatment-seeking alcohol-dependent (ALCs, n = 29; 14 male), illicit-stimulant-dependent (predominantly cocaine; STIMs, n = 25; 15 male), and alcohol- and illicit-stimulant-dependent (ALC/STIMs, n = 50; 35 male) participants with comorbid nicotine dependence were studied. Subjects had been abstinent from their drugs of choice for 41 (±18) days and were in short-term abstinence from tobacco (∼8-10 hours). Subjects received double-blind administration of either transdermal nicotine (high dose: 21/14 mg for men and women, respectively, or low dose: 7 mg) or placebo. The Logical Memory (LM) subtest from the Wechsler Memory Scale-Revised (WMS-R) was used to assess immediate and delayed verbal memory recall. Results indicated that STIMs receiving the high dose of nicotine recalled more words at immediate recall than STIMs who received placebo. Trend level differences were also noted at delayed recall between STIM nicotine and placebo doses. Nicotine failed to impact either recall in alcoholic subgroups. Although not the primary focus, results also revealed differences in the forgetting rates between the groups with the ALC/STIMs demonstrating the steepest forgetting slope. In summary, this study suggests that nicotine effects may be differentially experienced by substance-using subgroups; that nicotine may have a direct effect on memory; and that in considering neurocognitive processes (e.g., encoding vs. retrieval), underlying endpoint indicators (e.g., correct recall) may be critical in predicting outcomes.

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.

MDMA (ecstasy) use is associated with reduced BOLD signal change during semantic recognition in abstinent human polydrug users: a preliminary fMRI study

3,4-methylenedioxymethamphetamine (MDMA) users have impaired verbal memory, and voxel-based morphometry has shown decreased grey matter in Brodmann area (BA) 18, 21 and 45. Because these regions play a role in verbal memory, we hypothesized that MDMA users would show altered brain activation in these areas during performance of a functional magnetic resonance imaging (fMRI) task that probed semantic verbal memory. Polysubstance users enriched for MDMA exposure participated in a semantic memory encoding and recognition fMRI task that activated left BA 9, 18, 21/22 and 45. Primary outcomes were percent blood oxygen level-dependent signal change in left BA 9, 18, 21/22 and 45, accuracy and response time. During semantic recognition, lifetime MDMA use was associated with decreased activation in left BA 9, 18 and 21/22 but not 45. This was partly influenced by contributions from cannabis and cocaine use. MDMA exposure was not associated with accuracy or response time during the semantic recognition task. During semantic recognition, MDMA exposure was associated with reduced regional brain activation in regions mediating verbal memory. These findings partially overlap with previous structural evidence for reduced grey matter in MDMA users and may, in part, explain the consistent verbal memory impairments observed in other studies of MDMA users.

Imaging cognitive deficits in drug abuse

The neuropsychological network is a complex structure. To identify processes location and network capacity the brain imaging techniques together and in combination with other neuropsychological techniques and the expanding of well elaborated designs provide us with a multidimensional understanding, and contributes to the understanding of each illicit drug's character, which is of importance in designing of new treatment programs and clinical practice. Cannabis, MDMA, amphetamine, cocaine, and heroin abusers display both acute effects and chronic effects, deficits in attention, memory, and executive functioning. These deficits may last beyond the period of intoxication and cumulate with years of use. Cannabis users may recruit an alternative neural network as a compensatory mechanism during performance of tasks of attention. There is some evidence indicating the detrimental effects of cannabis on the maturing adolescent brain. Stimulant dependence is characterized by a distributed alteration of functional activation. Attenuated anterior and posterior cingulate activation, reduced inferior frontal and dorsolateral prefrontal cortex activation, and altered posterior parietal activation point towards an inadequate demand-specific processing of information. On an individual level they exhibit process-related brain activation differences that are consistent with a shift from context-specific, effortful processing to more stereotyped, habitual response generation. Finally, opiate use appears to decrease the ability to shift cognitive set and inhibit inappropriate response tendencies.

Performance on the Stroop predicts treatment compliance in cocaine-dependent individuals

Treatment dropout is a problem of great prevalence and stands as an obstacle to recovery in cocaine-dependent (CD) individuals. Treatment attrition in CD individuals may result from impairments in cognitive control, which can be reliably measured by the Stroop color-word interference task. The present analyses contrasted baseline performance on the color-naming, word-reading, and interference subtests of the Stroop task in CD subjects who completed a cocaine treatment trial (completers: N=50) and those who dropped out of the trial before completion (non-completers: N=24). A logistic regression analysis was used to predict trial completion using three models with the following variables: the Stroop task subscale scores (Stroop model); the Hamilton depression rating scale (HDRS) scores (HDRS model); and both the Stroop task subscale scores and HDRS scores (Stroop and HDRS model). Each model was able to significantly predict group membership (completers vs non-completers) better than a model based on a simple constant (HDRS model p=0.02, Stroop model p=0.006, and Stroop and HDRS model p=0.003). Models using the Stroop preformed better than the HDRS model. These findings suggest that the Stroop task can be used to identify cocaine-dependent subjects at risk for treatment dropout. The Stroop task is a widely available, reliable, and valid instrument that can be easily employed to identify and tailor interventions of at risk individuals in the hope of improving treatment compliance.

Chronic cocaine self-administration is associated with altered functional activity in the temporal lobes of non human primates

Previous studies utilizing a nonhuman primate model have shown that cocaine self-administration in its initial stages is accompanied by alterations in functional activity largely within the prefrontal cortex and ventral striatum. Continued cocaine exposure may considerably change this response. The purpose of the present investigation was to characterize the effects of reinforcing doses of cocaine on cerebral metabolism in a nonhuman primate model of cocaine self-administration, following an extended history of cocaine exposure, using the quantitative 2-[(14)C]deoxyglucose (2-DG) method. Rhesus monkeys were trained to self-administer 0.03 mg/kg/injection (n = 4) or 0.3 mg/kg/injection (n = 4) cocaine and compared to monkeys trained to respond under an identical schedule of food reinforcement (n = 6). Monkeys received 30 reinforcers per session for a total of 100 sessions. Metabolic mapping was conducted at the end of the final session. After this extended history, cocaine self-administration dose-dependently reduced glucose utilization throughout the striatum and prefrontal cortex similarly to the initial stages of self-administration. However, glucose utilization was also decreased in a dose-independent manner in large portions of the temporal lobe including the amygdala, hippocampus and surrounding neocortex. The recruitment of temporal structures indicates that the pattern of changes in functional activity has undergone significant expansion beyond limbic regions into association areas that mediate higher order cognitive and emotional processing. These data strongly contribute to converging evidence from human studies demonstrating structural and functional abnormalities in temporal and prefrontal areas of cocaine abusers, and suggest that substance abusers may undergo progressive cognitive decline with continued exposure to cocaine.

Influence of depression and HIV serostatus on the neuropsychological performance of injecting drug users

Depression is common in injecting drug users (IDUs), a group at significant risk for HIV infection. Moreover, both HIV infection and depression have been shown to adversely effect neurocognitive abilities. Understanding the effects of depression and HIV infection on the neurocognitive functioning of drug users is essential for appropriate management and/or treatment of these deficits in this population. Therefore, the purpose of the present study was to investigate the effects of depression and HIV status on cognitive functioning in 100 male and female IDUs. Participants were categorized into three groups of depression severity based on their scores on the Beck Depression Inventory: no depression, mild depression, and moderate to severe depression. The effects of depression and HIV serostatus as well as their interaction were assessed. Results indicated that regardless of serostatus, those with moderate to severe depression had lower scores on cognitive measures. These findings suggest that although depression contributes to poor neuropsychological performance in IDUs, this effect was not exacerbated by HIV infection. The finding also illustrates the importance of addressing depression-related neurocognitive deficits in IDUs.

Neurocognitive deficits in cocaine users: a quantitative review of the evidence

Studies on the neurocognitive effects of cocaine abuse are equivocal with respect to the specific types of deficits observed, although the vast majority of studies indicate that at least some deficits in certain broad functions such as attention, learning and memory, executive functions, and response speed exist. All of these studies based their results on null hypothesis statistical significance testing (NHSST). It is argued that effect size analysis, which provides information about the magnitude of difference, offers a more valid index of cognitive impairments in a population when compared to NHSST. Accordingly, the objective of the current study was to conduct an effect size analysis (or a meta-analysis in cases where the same test measure was utilized in more than one study) to determine the type and the magnitude of the specific cognitive deficits found as a result of cocaine use. Effect sizes were calculated for each test variable across 15 empirical studies that met inclusion criteria. The results from 481 cocaine users and 586 healthy normal controls revealed that cocaine use had the largest effect on several measures of attention (0.40 < d < 1.10). Moderate to large effect sizes (d > 0.50) were also obtained on tests of visual memory and working memory. Minimal effect sizes (d < 0.30) were obtained on tests of verbal fluency and other language functions and sensory-perceptual functions. Tests of executive functioning produced mixed findings and were interpreted in terms of degree rather than nature of impairment. The results are consistent with findings from neuroimaging and neurochemical studies that have found cocaine use to be associated with dysfunctions in the anterior cingulate gyrus and orbitofrontal cortex; these regions are highly implicated in the mediation of attentional and executive functions, respectively. Methodological limitations of the empirical studies included in the analysis are discussed.

Effect of ecstasy use on neuropsychological function: a study in Hong Kong

RATIONALE

Previous studies on the effects of ecstasy on neuropsychological performance have often recruited small sample sizes.

OBJECTIVES

The present study was conducted to validate previous findings regarding the effects of ecstasy consumption on neuropsychological performance.

METHOD

A comprehensive neuropsychological investigation was conducted in 100 abstinent ecstasy users and 100 matched non-user counterparts on standardized measures of working memory, verbal and non-verbal memory, verbal and figural fluency, and selective and switching attention.

RESULTS

Abstinent ecstasy users were impaired on verbal and non-verbal memory, complex attention, and verbal fluency, but not on working memory, relative to their non-user counterparts. Of particular interest was the fact that abstinent ecstasy users performed better on figural fluency relative to their non-user counterparts. In addition, only cumulative ecstasy consumption correlated with neuropsychological performances among abstinent ecstasy users. Canonical discriminant analysis yielded verbal and visual memory, switching attention, and verbal fluency as potential core neuropsychological variables for differentiating abstinent ecstasy users from non-users. Levels of depression and general non-verbal intelligence, as measured by the Beck Depression Inventory and the test of non-verbal Intelligence, respectively, were not likely to affect these findings, since these measures were matched between ecstasy users and non-users.

CONCLUSIONS

These findings suggest that previous ecstasy consumption can affect a wide range of neuropsychological performance, though figural fluency may be subsequently enhanced as a result of the phenomenon of "cortical disinhibition." Furthermore, measures of verbal and visual memory, switching attention, and verbal fluency may be particularly useful for differentiating abstinent ecstasy users from non-users.

The Effect of Alcohol on the Neuropsychological Functioning of Recently Abstinent Cocaine-dependent Subjects

Neuropsychological deficits in the areas of learning, memory, attention, and abstraction abilities have been associated with cocaine dependence, especially during the period of early abstinence. Although cocaine users tend to be multidrug users, few studies have focused on the combined effect of alcohol and cocaine on neuropsychological functioning. Consistent with prior research, results from the current study indicated that cocaine-dependent subjects showed a significantly greater degree of neuropsychological impairment as compared to controls. In addition, cocaine-dependent subjects with a history of alcohol disorder showed less memory impairment but similar impairments in attention and overall neuropsychological functioning as cocaine subjects with no such history. The vasodilatation produced by alcohol may attenuate some of the vasoconstriction and neurotoxic effects of cocaine, accounting for the fewer deficits in this group.

Severity of neuropsychological impairment in cocaine and alcohol addiction: association with metabolism in the prefrontal cortex

We used exploratory and confirmatory statistical approaches to study the severity of neuropsychological (NP) impairment in 42 crack/cocaine addicted subjects and in 112 comparison subjects (40 alcoholics and 72 controls). Twenty neuropsychological test indices most reliably defining predetermined cognitive domains were submitted to exploratory factor analysis. A four-dimensional model of neurocognitive function was derived: Verbal Knowledge, Visual Memory, Verbal Memory, and Attention/Executive functioning accounted for 63% of the variance. We then examined this model's association with resting glucose metabolism in the brain reward circuit measured with 2-deoxy-2[18F]fluoro-D-glucose positron emission tomography. Results revealed that (1) cocaine addicted individuals had a generalized mild level of neurocognitive impairment (<1 S.D. below control mean); and (2) controlling for age and education, relative metabolism in the dorsolateral prefrontal cortex significantly predicted the Visual Memory and Verbal Memory factors and relative metabolism in the anterior cingulate gyrus significantly predicted the Attention/Executive factor. Nevertheless, it remains to be determined whether metabolic changes in these regions are associated with addiction. Our results also suggest that compared to cocaine, alcohol has a more detrimental effect on Attention/Executive functioning, as assessed with traditional NP measures. We conclude that relative to other psychopathological disorders (such as schizophrenia), the severity of neuropsychological impairment in cocaine addiction is modest, albeit not indicative of the absence of neurocognitive dysfunction. The impact of such small differences in performance on quality of life, and possibly on craving and relapse, may be substantial. Tasks that simulate real-life decision-making or that target specific putative cognitive-behavioral or motivational-emotional mechanisms might offer greater sensitivity in characterizing the changes that accompany addiction to drugs. Obtaining valid estimates of alcohol use in cocaine addicted subjects is essential in characterizing neurocognitive functioning in individuals addicted to drugs.

Impaired executive function in male MDMA ("ecstasy") users

RATIONALE

Long-term users of ecstasy have shown impaired performance on a multitude of cognitive abilities (most notably memory, attention, executive function). Research into the pattern of MDMA effects on executive functions remains fragmented, however.

OBJECTIVES

To determine more systematically what aspects of executive function are affected by a history of MDMA use, by using a model that divides executive functions into cognitive flexibility, information updating and monitoring, and inhibition of pre-potent responses.

METHODS

MDMA users and controls who abstained from ecstasy and other substances for at least 2 weeks were tested with a computerized cognitive test battery to assess their abilities on tasks that measure the three submodalities of executive function, and their combined contribution on two more complex executive tasks. Because of sex-differential effects of MDMA reported in the literature, data from males and females were analyzed separately.

RESULTS

Male MDMA users performed significantly worse on the tasks that tap on cognitive flexibility and on the combined executive function tasks; no differences were found on the other cognitive tasks. Female users showed no impairments on any of the tasks.

CONCLUSIONS

The present data suggest that a history of MDMA use selectively impairs executive function. In male users, cognitive flexibility was impaired and increased perseverative behavior was observed. The inability to adjust behavior rapidly and flexibly may have repercussions for daily life activities.

Personality profile and neuropsychological test performance in chronic cocaine-abusers

Little is known about the association between personality disorders and neuropsychological test performance in chronic cocaine users. The aims of the present study were to (1) pinpoint the specific neuropsychological characteristics of chronic cocaine abusers, (2) analyze their personality profile, and (3) explore the association between personality traits and neuropsychological test performance. A sample of 42 drug-abusers (mean age = 34.15; SD = 6.73; mean educational level = 11.44; SD = 2.01) was selected from a state rehabilitation facility and was compared to a control group (mean age = 34.53; SD = 9.01; mean educational level = 12.29; SD = 1.31). The following information was collected for each subject: (1) A clinical history adapted from Horton (1996). (2) The Personality Assessment Inventory (PAI) (Morey, 1991). (3) A neuropsychological test battery including: Arithmetic and Digits subtests from the WAIS-R, California Verbal Learning Test, Trial Making Test, Verbal Fluency tests, Rey-Osterrieth Complex Figure, Wisconsin Card Sorting Test, Benton Visual Retention Test, Stroop Neurological Screening Test and Hooper Visual Organization. Thirty-seven of the drug-dependent subjects obtained an abnormal score in at least one PAI scale. The personality profile of the drug-dependent subjects found via the PAI pointed to a Borderline/Antisocial personality, frequently associated with mania features. In six of the drug-abusers, a normal personality profile was observed. Neuropsychological test performance scores were within the low average or borderline range. The most abnormal scores were observed in attention, memory, and executive functioning tests. The results did not show any robust association between personality profile and neuropsychological test performance.

Clinical neuropsychology in the criminal forensic setting

This article reviews the application of clinical neuropsychology to criminal court proceedings, a complex, underserved, yet growing area of neuropsychological practice. The authors write from the perspective that the audience is primarily neurorehabilitation clinicians with limited experience in criminal matters. Discussions on the theoretical differences between clinical and forensic work, the forensic evaluation process with conceptual model, historical and current perspectives on criminal competencies and responsibility, prediction of dangerousness, and professional and ethical issues often encountered in criminal neuropsychology are provided.

Neurocognitive dysfunction in dually-diagnosed patients: a potential roadblock to motivating behavior change

Substance abuse has been associated with cognitive dysfunction, such as problems with attention, reasoning, and memory. Certain psychiatric disorders also have been associated with cognitive difficulties, thus placing dually-diagnosed patients at high risk for cognitive impairment that could interfere with successful entry into or completion of therapy. Twenty-two dually-disordered inpatients were administered the Brief Readiness to Change Questionnaire to measure levels of motivation to change substance use, and a neuropsychological test battery that included the Wechsler Adult Intelligence Scale-Revised (WAIS-R), the Halstead Category Test (HCT), and the Wechsler Memory Scale-Revised (WMS-R). Higher general intellectual, executive, and memory functioning were significantly related to greater scores in readiness to change substance abuse in this sample. Cognitive ability may be an important variable to consider in the motivation and treatment of dually-diagnosed patients.

Amlodipine treatment of cocaine dependence

Preclinical studies indicate that dihydropyridine-type calcium channel antagonists modulate dopamine neurotransmitter function and can reduce cocaine-reinforced behaviors. Amlodipine, a long-acting dihydropyridine-type calcium channel antagonist related to isradipine and nifedipine, was administered in open label fashion for 12 weeks to 26 cocaine-dependent patients. In subjects expressing cocaine craving, craving significantly declined during the course of the 12 weeks. Five individuals reported flushing, headache, fatigue, nocturia, nausea, and lightheadedness. No conclusions regarding efficacy can be made due to the small number of subjects and the open-label design.

Effects of crack cocaine on neurocognitive function

Because crack cocaine appears to have a preferential effect on the metabolic and electrophysiological activity of the frontal and temporal regions of the brain (Pascual-Leone et al., 1991a, 1991b; Volkow, 1992), we hypothesized that cognitive measures of those regions would be impaired in crack cocaine users relative to measures in normal volunteers. We used logistic regression to determine the relationship of cocaine usage to neuropsychological test performance. We compared 38 patients with an average of 3.6 (SD = 2.5) years of crack cocaine use and 24.5 (SD = 28.1) days of abstinence to 54 normal volunteers on a battery of neuropsychological tests. Statistical adjustments were made for the effects of age, education, socioeconomic class, and level of depression. Our findings were mixed with regard to purported measures of executive/frontal functioning, with worse performance associated with cocaine usage on the Booklet Categories Test, but better performance associated on others (number of categories on the Wisconsin Card Sorting Test, Controlled Oral Word Association). Cocaine usage was associated with impairment on measures of spatial, but not verbal memory, confrontation naming, and Trail-making Test, Part B, a measure of perceptual-motor speed and cognitive flexibility. In summary, it appears that continuous crack cocaine use produces a dissociative pattern in neuropsychological test performance with improvement on some measures, but deterioration on others. The permanence of these effects remains to be determined with longitudinal studies.

Cognitive effects of cocaine and polydrug abuse

One hundred and eighty-three participants were divided into three groups containing: 61 cocaine-dependent; 59 polydrug-dependent; and 63 normal subjects. All were evaluated using a basic neuropsychological assessment battery. The dependent groups exhibited significantly lower scores on short-term memory, attention, and concept formation tests. Performance on some subtests correlated negatively with the length of dependency and frequency of substance use. As compared with the control group, the dependent groups exhibited significant differences in the following personal and family areas: (a) depression and anxiety traits; (b) self-aggression and lack of fear in childhood; (c) family history of substance dependency; and (d) difficulties with interpersonal relationships. The operation of predisposing developmental factors for substance dependence is suggested.

The California Verbal Learning Test: psychometric characteristics and clinical application

The California Verbal Learning Test (CVLT) is a popular clinical and research test that claims to measure key constructs in cognitive psychology such as repetition learning, serial position effects, semantic organization, intrusions, and proactive interference. The psychometric characteristics of the CVLT are reviewed and related to the test's clinical utility. The utility of the CVLT is shown to be limited by its poor standardization and inflated norms. Further, the validity is limited because the CVLT uses multiple trials whereas the constructs it purports to measure are based on single-trial paradigms. The review proposes modifications to the CVLT and guidelines for its clinical use. It concludes that if the limitations of the CVLT are recognized, it can still make a useful contribution to the clinical assessment of verbal learning and memory.

Cocaine-induced cerebrovascular impairment: challenges to neuropsychological assessment

The patient who presents for evaluation and/or subsequent treatment of a neurological or psychiatric complaint accompanied by a positive history of substance abuse has generally received only modest attention in the clinical practice literature. Significantly more clinical attention has focused on the neurobehavioral sequelae of more pronounced brain insults, despite the rapid emergence of literature detailing psychopharmacologic-induced changes in brain-behavior functioning. This article describes recent clinical research findings related to the neuropsychology of cocaine use and associated issues of neurobiology and psychopharmacology. A description of strategies that have proven effective for assessing this population will be discussed. An emphasis on neurocognitive impairment that may precede as well as occur consequent to cocaine use are also examined. The literature reviewed here generally supports the conclusion that subgroups of cocaine abusing patients may demonstrate sustained brain perfusion anomalies and persistent neurocognitive deficits.