Functional magnetic resonance imaging of cocaine craving

Decision-making and prepotent response inhibition functions in excessive internet users

INTRODUCTION

Excessive Internet use (EIU), also described as Internet addiction or pathological Internet use, has already become a serious social problem around the world. Some researchers consider EIU as a kind of behavioral addiction. However, there are few experimental studies on the cognitive functions of excessive Internet users (EIUers) and limited data are available to compare EIU with other addictive behaviors, such as drug abuse and pathological gambling.

METHODS

In the present study, we examined EIUers' functions of decision-making and prepotent response inhibition. Two groups of participants, EIUers and controls, were compared on these two functions by using a Gambling Task and a Go/no-go Task, respectively.

RESULTS

Compared with controls, EIUers selected significantly less net decks in the Gambling Task (P=.007). Furthermore, the EIUers made progress in selecting strategy, but more slowly than did the control group (EIUers, chunk 3 > chunk 1, P<.001; controls, chunk 2 > chunk 1, P<.001). Interestingly, EIUers' accuracy during the no-go condition was significantly higher than that of controls (P=.018).

CONCLUSION

These results showed some similarities and dissimilarities between EIU and other addictive behaviors such as drug abuse and pathological gambling. The findings from the Gambling Task indicated that EIUers have deficits in decision-making function, which are characterized by a strategy learning lag rather than an inability to learn from task contingencies. EIUers' better performance in the Go/no-go Task suggested some dissociation between mechanisms of decision-making and those of prepotent response inhibition. However, EIUers could hardly suppress their excessive online behaviors in real life. Their ability of inhibition still needs to be further studied with more specific assessments.

Neural mechanisms underlying drug-related cue distraction in active cocaine users

Human drug dependence routinely features a difficulty with disengaging attention from drug-related stimuli, a symptom previously shown to be predictive of relapse during treatment. We examined the neural mechanisms underlying this attentional bias in cocaine users, varying working memory (WM) load to reflect the demands imposed by ruminative craving thoughts. Sixteen active users of cocaine were administered a WM task that manipulated the requirement for selective attention by varying the background contents, cocaine-related or neutral, upon which a recall probe item was shown. Behavioural and fMRI data were collected. Cocaine users had significantly poorer attentional control under high WM demands, suffering both increased response times and reduced recall accuracy, with this effect more pronounced for cocaine stimuli (when compared to neutral stimuli). The presence of background cocaine stimuli was associated with increases in occipital cortex activity, consistent with increased visual processing of the irrelevant stimuli for these trials. In addition, the cocaine stimuli were associated with increased right prefrontal activity with those participants with higher levels of right prefrontal activity having lower levels of attentional bias. Cocaine users under high cognitive demands had difficulty modulating the neural mechanisms underlying cognitive control which appear necessary for restricting the visual processing of task-irrelevant, but salient drug-related, stimuli, a finding that may be relevant to identifying those at most risk of relapse.

Drug addiction and the memory systems of the brain

We review drug addiction from the perspective of the hypothesis that drugs of abuse interact with distinct brain memory systems. We focus on emotional and procedural forms of memory, encompassing Pavlovian and instrumental conditioning, both for action-outcome and for stimulus-response associations. Neural structures encompassed by these systems include the amygdala, hippocampus, nucleus accumbens, and dorsal striatum. Additional influences emanate from the anterior cingulate and prefrontal cortex, which are implicated in the encoding and retrieval of drug-related memories that lead to drug craving and drug use. Finally, we consider the ancillary point that chronic abuse of many drugs may impact directly on neural memory systems via neuroadaptive and neurotoxic effects that lead to cognitive impairments in which memory dysfunction is prominent.

Cortical activation during delay discounting in abstinent methamphetamine dependent individuals

BACKGROUND

Methamphetamine (MA)-dependent individuals prefer smaller immediate over larger delayed rewards in delay discounting (DD) tasks. Human and animal data implicate ventral (amygdala, ventral striatum, ventrolateral prefrontal cortex insula) and dorsal (dorsolateral prefrontal cortex, dorsal anterior cingulate cortex and posterior parietal cortex) systems in DD decisions. The ventral system is hypothesized to respond to the salience and immediacy of rewards while the dorsal system is implicated in the process of comparison and choice.

METHODS

We used functional Magnetic Resonance Imaging to probe the neural correlates of DD in 19 recently abstinent MA-dependent patients and 17 age- and gender-matched controls.

RESULTS

Hard DD choices were associated with greatest activation in bilateral middle cingulate, posterior parietal cortex (PPC), and the right rostral insula. Control subjects showed more activation than MA patients bilaterally in the precuneus and in the right caudate nucleus, anterior cingulate cortex (ACC), and dorsolateral prefrontal cortex (DLPFC). Magnitude of discounting was correlated with activity in the amygdala, DLPFC, posterior cingulate cortex and PPC.

CONCLUSIONS

Our findings were consistent with a model wherein dorsal cognitive systems modulate the neural response of ventral regions. Patients addicted to MA, who strongly prefer smaller immediate over larger delayed rewards, activate the dorsal cognitive control system in order to overcome their preference. Activation of the amygdala during choice of delayed rewards was associated with a greater degree of discounting, suggesting that heavily discounting MA-dependent individuals may be more responsive to the negative salience of delayed rewards than controls.

Review. The neurobiology of pathological gambling and drug addiction: an overview and new findings

Gambling is a prevalent recreational behaviour. Approximately 5% of adults have been estimated to experience problems with gambling. The most severe form of gambling, pathological gambling (PG), is recognized as a mental health condition. Two alternate non-mutually exclusive conceptualizations of PG have considered it as an obsessive-compulsive spectrum disorder and a 'behavioural' addiction. The most appropriate conceptualization of PG has important theoretical and practical implications. Data suggest a closer relationship between PG and substance use disorders than exists between PG and obsessive-compulsive disorder. This paper will review data on the neurobiology of PG, consider its conceptualization as a behavioural addiction, discuss impulsivity as an underlying construct, and present new brain imaging findings investigating the neural correlates of craving states in PG as compared to those in cocaine dependence. Implications for prevention and treatment strategies will be discussed.

The hidden island of addiction: the insula

Most prior research on the neurobiology of addiction has focused on the role of subcortical systems, such as the amygdala, the ventral striatum and mesolimbic dopamine system, in promoting the motivation to seek drugs. Recent evidence indicates that a largely overlooked structure, the insula, plays a crucial part in conscious urges to take drugs. The insula has been highlighted as a region that integrates interoceptive (i.e. bodily) states into conscious feelings and into decision-making processes that involve uncertain risk and reward. Here, we propose a model in which the processing of the interoceptive effects of drug use by the insula contributes to conscious drug urges and to decision-making processes that precipitate relapse.

Modulation of brain response to emotional images by alcohol cues in alcohol-dependent patients

Alcohol is often used to modulate mood states. Alcohol drinkers report that they use alcohol both to enhance positive affect and to reduce dysphoria, and alcohol-dependent patients specifically state reduction of negative affect as a primary reason for drinking. The current study proposes that alcohol cues may reduce negative affect in alcoholics. We used functional magnetic resonance imaging to examine brain activation in response to combination images that juxtaposed negative or positive International Affective Picture System (IAPS) images with an alcohol or non-alcohol-containing beverage. We found that in the absence of the alcohol cue, alcoholics showed more activation to negative than to positive images and greater activation than controls to negative images. When the IAPS images were presented with the alcohol cue, there was a decreased difference in activation between the positive and negative images among the alcoholics, and a decreased difference in response to the negative images between controls and alcoholics. Additionally, in the neutral-beverage conditions, anxiety ratings significantly predicted activation in the right parahippocampal gyrus but did not predict activation when the alcohol cues were presented. In conclusion, the alcohol cues may have modulated cortical networks involved in the processing of emotional stimuli by eliciting a conditioned response in the alcoholics, but not in the controls, which may have decreased responsiveness to the negative images.

A somatic marker theory of addiction

Similar to patients with ventromedial prefrontal cortex (VMPC) lesions, substance abusers show altered decision-making, characterized by a tendency to choose the immediate reward, at the expense of negative future consequences. The somatic marker model proposes that decision-making depends on neural substrates that regulate homeostasis, emotion and feeling. According to this model, there should be a link between alterations in processing emotions in substance abusers, and their impairments in decision-making. Growing evidence from neuroscientific studies indicate that core aspects of addiction may be explained in terms of abnormal emotional/homeostatic guidance of decision-making. Behavioral studies have revealed emotional processing and decision-making deficits in substance abusers. Neuroimaging studies have shown that altered decision-making in addiction is associated with abnormal functioning of a distributed neural network critical for the processing of emotional information, and the experience of "craving", including the VMPC, the amygdala, the striatum, the anterior cingulate cortex, and the insular/somato-sensory cortices, as well as non-specific neurotransmitter systems that modulate activities of neural processes involved in decision-making. The aim of this paper is to review this growing evidence, and to examine the extent to which these studies support a somatic marker theory of addiction. We conclude that there are at least two underlying types of dysfunction where emotional signals (somatic markers) turn in favor of immediate outcomes in addiction: (1) a hyperactivity in the amygdala or impulsive system, which exaggerates the rewarding impact of available incentives, and (2) hypoactivity in the prefrontal cortex or reflective system, which forecasts the long-term consequences of a given action.

Region-specific involvement of AMPA/Kainate receptors in Fos protein expression induced by cocaine-conditioned cues

This study investigated the effects of the AMPA/Kainate receptor antagonist, NBQX, on cue-elicited cocaine-seeking behavior and concomitant changes in Fos protein expression. After cocaine self-administration training, rats underwent 24 days of abstinence during which they were exposed daily either to the self-administration environment with response-contingent cues previously paired with cocaine infusions available (Extinction group) or to an alternate environment (No Extinction group). Subsequently, rats were tested for cocaine-seeking behavior (i.e., operant responses without cocaine reinforcement) elicited by the cocaine-associated cues after pretreatment with either vehicle or NBQX (10 mg/kg, IP). NBQX markedly attenuated cue-elicited cocaine-seeking behavior relative to vehicle pretreatment in the No Extinction group and also decreased cue-elicited Fos protein expression in a region-specific manner in the anterior cingulate and orbitofrontal cortices, basolateral amygdala, nucleus accumbens core, and dorsal caudate-putamen, suggesting involvement of AMPA glutamate systems in specific subregions of the neuronal circuitry activated by cocaine cues.

Beta-endorphin and drug-induced reward and reinforcement

Although drugs of abuse have different acute mechanisms of action, their brain pathways of reward exhibit common functional effects upon both acute and chronic administration. Long known for its analgesic effect, the opioid beta-endorphin is now shown to induce euphoria, and to have rewarding and reinforcing properties. In this review, we will summarize the present neurobiological and behavioral evidences that support involvement of beta-endorphin in drug-induced reward and reinforcement. Currently, evidence supports a prominent role for beta-endorphin in the reward pathways of cocaine and alcohol. The existing information indicating the importance of beta-endorphin neurotransmission in mediating the reward pathways of nicotine and THC, is thus far circumstantial. The studies described herein employed diverse techniques, such as biochemical measurements of beta-endorphin in various brain sites and plasma, and behavioral measurements, conducted following elimination (via administration of anti-beta-endorphin antibodies or using mutant mice) or augmentation (by intracerebral administration) of beta-endorphin. We suggest that the reward pathways for different addictive drugs converge to a common pathway in which beta-endorphin is a modulating element. Beta-endorphin is involved also with distress. However, reviewing the data collected so far implies a discrete role, beyond that of a stress response, for beta-endorphin in mediating the substance of abuse reward pathway. This may occur via interacting with the mesolimbic dopaminergic system and also by its interesting effects on learning and memory. The functional meaning of beta-endorphin in the process of drug-seeking behavior is discussed.

Effect of naltrexone and ondansetron on alcohol cue-induced activation of the ventral striatum in alcohol-dependent people

CONTEXT

Medication for the treatment of alcoholism is currently not particularly robust. Neuroimaging techniques might predict which medications could be useful in the treatment of alcohol dependence.

OBJECTIVE

To explore the effect of naltrexone, ondansetron hydrochloride, or the combination of these medications on cue-induced craving and ventral striatum activation.

DESIGN

Functional brain imaging was conducted during alcohol cue presentation.

SETTING

Participants were recruited from the general community following media advertisement. Experimental procedures were performed in the magnetic resonance imaging suite of a major training hospital and medical research institute.

PATIENTS

Ninety non-treatment-seeking alcohol-dependent (by DSM-IV criteria) and 17 social drinking (< 14 drinks per week) paid volunteers recruited through advertisements at an academic center.

INTERVENTIONS

A taste of alcohol and a series of alcohol-related pictures, neutral beverage pictures, and visual control images were provided to volunteers after 7 days of double-blind randomly assigned daily dosing with 50 mg of naltrexone (n = 23), 0.50 mg of ondansetron hydrochloride (n = 23), the combination of the 2 medications (n = 20), or matching placebos (n = 24).

MAIN OUTCOME MEASURES

Difference in brain blood oxygen level-dependent magnetic resonance when viewing alcohol pictures vs neutral beverage pictures with a particular focus on ventral striatum activity comparison across medication groups. Self-ratings of alcohol craving.

RESULTS

The combination treatment decreased craving for alcohol. Naltrexone with (P = .02) or without (P = .049) ondansetron decreased alcohol cue-induced activation of the ventral striatum. Ondansetron by itself was similar to naltrexone and the combination in the overall analysis but intermediate in a region-specific analysis.

CONCLUSIONS

Consistent with animal data that suggest that both naltrexone and ondansetron reduce alcohol-stimulated dopamine output in the ventral striatum, the current study found evidence that these medications, alone or in combination, could decrease alcohol cue-induced activation of the ventral striatum, consistent with their putative treatment efficacy.

Imaging the addicted human brain

Modern imaging techniques enable researchers to observe drug actions and consequences as they occur and persist in the brains of abusing and addicted individuals. This article presents the five most commonly used techniques, explains how each produces images, and describes how researchers interpret them. The authors give examples of key findings illustrating how each technique has extended and deepened our knowledge of the neurobiological bases of drug abuse and addiction, and they address potential clinical and therapeutic applications.

Homers regulate drug-induced neuroplasticity: implications for addiction

Drug addiction is a chronic, relapsing disorder, characterized by an uncontrollable motivation to seek and use drugs. Converging clinical and preclinical observations implicate pathologies within the corticolimbic glutamate system in the genetic predisposition to, and the development of, an addicted phenotype. Such observations pose cellular factors regulating glutamate transmission as likely molecular candidates in the etiology of addiction. Members of the Homer family of proteins regulate signal transduction through, and the trafficking of, glutamate receptors, as well as maintain and regulate extracellular glutamate levels in corticolimbic brain regions. This review summarizes the existing data implicating the Homer family of protein in acute behavioral and neurochemical sensitivity to drugs of abuse, the development of drug-induced neuroplasticity, as well as other behavioral and cognitive pathologies associated with an addicted state.

Development and initial validation of a caffeine craving questionnaire

Craving for caffeine has received little empirical attention, despite considerable research into the potential for caffeine dependence. The main aim of this study was to develop, and initially validate, a multi-item, multidimensional instrument to measure cravings for caffeine. Participants were 189 caffeine consumers who completed the Questionnaire of Caffeine Cravings, which was based on the Questionnaire of Smoking Urges (QSU), in one of five naturally occurring periods of abstinence; 1-15 min; 16-120 mins; 3-7 h; 12-48 h and +48 h. Exploratory factor analysis suggested a three-factor solution best described the data; Factor 1 reflected strong desires, intentions and positive reinforcement; Factor 2 reflected mild/general positive and negative reinforcement and Factor 3 reflected functional/mood-based negative reinforcement. Significantly higher Factor 1 and Factor 2 scores were recorded for high frequency users; significantly higher Factor 1 and Factor 3 scores were recorded as a function of increased levels of dependence. Duration of abstinence did not significantly effect cravings across all three factors. Regression analyses suggested level of dependence best predicted both current cravings and frequency of daily use. These findings suggest caffeine cravings may be conceptualized multidimensionally and further validates the use of multidimensional, multi-item instruments. Cravings for caffeine may manifest and be detected across varying levels of dependence and, frequency of use and independently of duration of abstinence.

Inhibitory control and emotional stress regulation: neuroimaging evidence for frontal-limbic dysfunction in psycho-stimulant addiction

This review focuses on neuroimaging studies that examined stress processing and regulation and cognitive inhibitory control in patients with psycho-stimulant addiction. We provide an overview of these studies, summarizing converging evidence and discrepancies as they occur in the literature. We also adopt an analytic perspective and dissect these psychological processes into their sub-components, to identify the neural pathways specific to each component process and those that are more specifically involved in psycho-stimulant addiction. To this aim we refer frequently to studies conducted in healthy individuals. Despite the separate treatment of stress/affect regulation, stress-related craving or compulsive drug seeking, and inhibitory control, neural underpinnings of these processes overlap significantly. In particular, the ventromedial prefrontal regions including the anterior cingulate cortex, amygdala and the striatum are implicated in psychostimulant dependence. Our overarching thesis is that prefrontal activity ensures intact emotional stress regulation and inhibitory control. Altered prefrontal activity along with heightened striatal responses to addicted drug and drug-related salient stimuli perpetuates habitual drug seeking. Further studies that examine the functional relationships of these neural systems will likely provide the key to understanding the mechanisms underlying compulsive drug use behaviors in psycho-stimulant dependence.

Explaining the escalation of drug use in substance dependence: models and appropriate animal laboratory tests

Escalation of drug use, a hallmark of drug dependence, has traditionally been interpreted as reflecting the development of tolerance to the drug's effects. However, on the basis of animal behavioral data, several groups have recently proposed alternative explanations, i.e. that such an escalation of drug use might not be based on (1) tolerance, but rather be indicative of (2) sensitization to the drug's reinforcing effect, (3) reward allostasis, (4) an increase in the incentive salience of drug-associated stimuli, (5) an increase in the reinforcing strength of the drug reinforcer relative to alternative reinforcers, or (6) habit formation. From the pharmacological perspective, models 1-3 allow predictions about the change in the shape of drug dose-effect curves that are based on mathematically defined models governing receptor-ligand interaction and signal transduction. These predictions are tested in the present review, which also describes the other currently championed models for drug use escalation and other components of apparent 'reinforcement' (in its original meaning, like 'tolerance' or 'sensitization', a purely descriptive term). It evaluates the animal experimental approaches employed to support or prove the existence of each of the models and reinforcement components, and recapitulates the clinical evidence, which strongly suggests that escalation of drug use is predominantly based on an increase in the frequency of intoxication events rather than an increase in the dose taken at each intoxication event. Two apparent discrepancies in animal experiments are that (a) sensitization to overall reinforcement has been found more often for psychostimulants than for opioids, and that (b) tolerance to the reinforcing and other effects has been observed more often for opioids than for cocaine. These discrepancies are resolved by the finding that cocaine levels seem to be more tightly regulated at submaximum reinforcing levels than opioid levels are. Consequently, animals self-administering opioids are more likely to expose themselves to higher above-threshold doses than animals self-administering psychostimulants, rendering the development of tolerance to opioids more likely than tolerance to psychostimulants. The review concludes by making suggestions on how to improve the current behavioral experimental approaches.

Imaging stress- and cue-induced drug and alcohol craving: association with relapse and clinical implications

Stress- and drug-related cues are major factors contributing to high rates of relapse in addictive disorders. Brain imaging studies have begun to identify neural correlates of stress and drug cue-induced craving states. Findings indicate considerable overlap in neural circuits involved in processing stress and drug cues with activity in the corticostriatal limbic circuitry underlying both affective and reward processing. More recent efforts have begun to identify the relationships between neural activity during stress and drug cue exposure and drug relapse outcomes. Findings suggest medial prefrontal, anterior and posterior cingulate, striatal and posterior insula regions to be associated with relapse outcomes. Altered function in these brain regions is associated with stress-induced and drug cue-induced craving states and an increased susceptibility to relapse. Such alterations can serve as markers to identify relapse propensity and a more severe course of addiction. Efficacy of pharmacological and behavioral treatments that specifically target stress and cue-induced craving and arousal responses may also be assessed via alterations in these brain correlates.

Conditioned dopamine release in humans: a positron emission tomography [11C]raclopride study with amphetamine

Studies in laboratory rodents suggest that previously neutral stimuli repeatedly paired with the administration of drugs of abuse can acquire the ability to increase striatal dopamine release. This conditioned neurochemical response is believed to prompt drug seeking in animals and has been hypothesized to contribute to drug craving and relapse in substance abusers. In the present study, we used positron emission tomography and [11C]raclopride to investigate whether amphetamine-predictive stimuli can elicit striatal dopamine release in humans. Nine healthy male volunteers received a capsule containing amphetamine tablets (0.3 mg/kg) on three separate occasions approximately every other day (mean +/- SD, 2.25 +/- 1.13 d apart) in the same environment (scanner suite). At least 2 weeks later, the amphetamine was switched to a placebo of identical appearance and given in the same environmental context. [11C]Raclopride binding to dopamine D(2/3) receptors was assessed after exposure to the first amphetamine-containing pill, after placebo administration, and during a control (no pill) scan. Relative to the control scan, amphetamine administration decreased [11C]raclopride binding potential by 22% in the ventral striatum and 11% in the putamen. Placebo also decreased [11C]raclopride binding potential in the ventral striatum and did so with the same amplitude as amphetamine (23%). These results suggest that cues associated with amphetamine increase dopamine transmission, providing evidence that this system is involved in reward prediction in humans.

Cocaine sensitization and dopamine mediation of cue effects in rodents, monkeys, and humans: areas of agreement, disagreement, and implications for addiction

BACKGROUND

Sensitization of mesocorticolimbic dopamine projections has been a valuable model of neurobiological adaptation to chronic exposure to cocaine and other psychostimulants.

DISCUSSIONS

In addition to providing an explanation of exaggerated responses to drugs that might explain their increased ability to serve as reinforcers, sensitization has also been incorporated into influential theories of how drug associated cues can acquire increased salience and incentive motivation. However, almost all of the work exploring behavioral and neurochemical sensitization has been conducted in rodents. Importantly, the relatively small amount of work conducted in human and nonhuman primates differs from the rodent work in some important regards. This review will examine areas of convergence and divergence between the rodent and primate literature on sensitization and the ability of drug associated environmental cues to elicit dopamine release. The implications of this comparison for expanding addiction research beyond dopaminergic mechanisms in the striatum/nucleus accumbens will be considered.

Corticolimbic dysregulation and chronic methamphetamine abuse

AIMS

This review aims to present and interpret evidence that methamphetamine dependence is associated with disorder of brain function that is required for top-down control of behavior.

APPROACH

Presented here are findings from brain imaging studies of human research participants with histories of chronic methamphetamine abuse in the context of functional consequences and implications for treatment of their dependence on methamphetamine.

FINDINGS

Brain imaging studies have revealed differences in the brains of research participants who have used methamphetamine chronically and then abstained from taking the drug, compared with healthy control subjects. These abnormalities are prominent in cortical and limbic systems, and include deficits in markers of dopaminergic and serotonergic neurotransmitter systems, differences in glucose metabolism and deficits in gray matter. These abnormalities accompany cognitive deficits, including evidence of impaired inhibitory control.

CONCLUSION

Cortical deficits in abstinent methamphetamine abusers can affect a wide range of functions that can be important for success in maintaining drug abstinence. These include but are not limited to modulation of responses to environmental stimuli as well as internal triggers that can lead to craving and relapse. Potential therapies may combine behavioral approaches with medications that can improve cognitive control.

The nucleus accumbens and Pavlovian reward learning

The ability to form associations between predictive environmental events and rewarding outcomes is a fundamental aspect of learned behavior. This apparently simple ability likely requires complex neural processing evolved to identify, seek, and use natural rewards and redirect these activities based on updated sensory information. Emerging evidence from both animal and human research suggests that this type of processing is mediated in part by the nucleus accumbens (NAc) and a closely associated network of brain structures. The NAc is required for a number of reward-related behaviors and processes specific information about reward availability, value, and context. In addition, this structure is critical for the acquisition and expression of most Pavlovian stimulus-reward relationships, and cues that predict rewards produce robust changes in neural activity in the NAc. Although processing within the NAc may enable or promote Pavlovian reward learning in natural situations, it has also been implicated in aspects of human drug addiction, including the ability of drug-paired cues to control behavior. This article provides a critical review of the existing animal and human literature concerning the role of the NAc in Pavlovian learning with nondrug rewards and considers some clinical ture concerning the role of the NAc in Pavlovian learning with nondrug implications of these findings.

Location, location: using functional magnetic resonance imaging to pinpoint brain differences relevant to stimulant use

AIMS

The purpose of this review is to summarize the neural substrate dysfunctions and disrupted cognitive, affective and experiential processes observed in methamphetamine and cocaine-dependent individuals.

METHODS

We reviewed all publications in PubMed that conducted comparison studies between healthy volunteers and cocaine-, amphetamine- or methamphetamine-dependent individuals using functional magnetic resonance imaging.

RESULTS

Stimulant dependence is characterized by a distributed alteration of functional activation to a number of experimental paradigms. 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. Processes reported most consistently to be deficient in these functional neuroimaging studies include inhibitory control, executive functioning and decision-making.

CONCLUSION

One emerging theme is that stimulant-dependent individuals show specific, rather than generic, brain activation differences, i.e. instead of showing more or less brain activation regardless of task, they exhibit process-related brain activation differences that are consistent with a shift from context-specific, effortful processing to more stereotyped, habitual response generation.

Fos and glutamate AMPA receptor subunit coexpression associated with cue-elicited cocaine-seeking behavior in abstinent rats

Cocaine-associated cues acquire incentive motivational effects that manifest as craving in humans and cocaine-seeking behavior in rats. We have reported an increase in neuronal activation in rats, measured by Fos protein expression, in various limbic and cortical regions following exposure to cocaine-associated cues. This study examined whether the conditioned neuronal activation involves glutamate AMPA receptors by measuring coexpression of Fos and AMPA glutamate receptor subunits (GluR1, GluR2/3, or GluR4). Rats trained to self-administer cocaine subsequently underwent 22 days of abstinence, during which they were exposed daily to either the self-administration environment with presentations of the light/tone cues previously paired with cocaine infusions (Extinction group) or an alternate environment (No Extinction group). All rats were then tested for cocaine-seeking behavior (i.e. responses without cocaine reinforcement) and Fos and AMPA glutamate receptor subunits were measured postmortem using immunocytochemistry. The No Extinction group exhibited increases in cocaine-seeking behavior and Fos expression in limbic and cortical regions relative to the Extinction group. A large number of Fos immunoreactive cells coexpressed GluR1, GluR2/3, and GluR4, suggesting that an action of glutamate at AMPA receptors may in part drive cue-elicited Fos expression. Importantly, there was an increase in the percentage of cells colabeled with Fos and GluR1 in the anterior cingulate and nucleus accumbens shell and cells colabeled with Fos and GluR4 in the infralimbic cortex, suggesting that within these regions, a greater, and perhaps even different, population of AMPA receptor subunit-expressing neurons is activated in rats engaged in cocaine-seeking behavior.

Role of the anterior cingulate and medial orbitofrontal cortex in processing drug cues in cocaine addiction

Our goal in the current report was to design a new functional magnetic resonance imaging (fMRI) task to probe the role of the anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC) in processing of salient symptom-related cues during the simultaneous performance of an unrelated task in drug-addicted persons. We used a novel fMRI color-word drug Stroop task in 14 individuals with cocaine use disorders; subjects had to press for color of drug vs. matched neutral words. Although there were no accuracy or speed differences between the drug and neutral conditions in the current sample of subjects, drug words were more negatively valenced than the matched neutral words. Further, consistent with prior reports in individuals with other psychopathologies using different Stroop fMRI paradigms, our more classical color-word Stroop design revealed bilateral activations in the caudal-dorsal anterior cingulate cortex (cdACC) and hypoactivations in the rostro-ventral anterior cingulate cortex/medial orbitofrontal cortex (rACC/mOFC). A trend for larger rACC/mOFC hypoactivations to the drug than neutral words did not survive whole-brain corrections. Nevertheless, correlation analyses indicated that (1) the more the cdACC drug-related activation, the more negative the valence attributed to the drug words (r=-0.86, P<0.0001) but not neutral words; and (2) the more the rACC/mOFC hypoactivation to drug minus neutral words, the more the errors committed specifically to the drug minus neutral words (r=0.85, P<0.0001). Taken together, results suggest that this newly developed drug Stroop fMRI task may be a sensitive biobehavioral assay of the functions recruited for the regulation of responses to salient symptom-related stimuli in drug-addicted individuals.

Error-processing deficits in patients with cocaine dependence

Cocaine abuse and addiction can be characterized by a persisting use of cocaine in the face of adverse consequences. In the present study we focus on one specific element of adverse consequences: the making of errors. The aim of this study was to determine whether cocaine-dependent persons have error-processing deficits as measured using error-related negativity (ERN) and error positivity (Pe). Event-related potentials (ERPs) during an Eriksen flanker task were recorded from cocaine-dependent patients and a control group. Cocaine-addicted patients showed reduced ERN and Pe components as compared to a control group. On the behavioral level, patients showed reduced post-error accuracy improvement. The present findings reveal that cocaine addiction is associated with reduced error processing and impaired behavioral correction of errors after an error is made. These deficits may be associated with a compromised dopamine system. It is argued that these cognitive deficits may contribute to the maintenance of the cocaine addiction.

Effects of expectancy and abstinence on the neural response to smoking cues in cigarette smokers: an fMRI study

Cues associated with drug taking can trigger relapse, drug seeking, and craving in addicted individuals. Behavioral studies suggest that drug availability and withdrawal can affect the individual response to drug cues. Moreover, the importance of subjective craving in cue-induced relapse has been questioned and an alternative model put forward according to which drug cues trigger habitual drug-seeking behaviors independently of craving. We used functional magnetic resonance imaging to compare the brain response to smoking and control videotapes in 20 healthy smokers, while varying their expectancy to smoke and abstinence levels. The neural response to cigarette cues was strongly modulated by expectancy and, to a lesser extent, abstinence. In people expecting to smoke immediately after the scan, smoking cues activated brain areas implicated in arousal, attention, and cognitive control. However, when subjects knew they would not be allowed to smoke for 4 h, there was almost no brain activation in response to smoking cues, despite equivalent reported levels of craving. In the dorsolateral prefrontal cortex, the neural response was a function of both craving and expectancy. Thalamo-cingulate connectivity, thought to be an index of arousal, was greater during expectancy than nonexpectancy. Our findings confirm the importance of expectancy in the neural response to drug cues, and lend support to the theory that these cues act on brain areas involved in arousal and attention.

Increased occupancy of dopamine receptors in human striatum during cue-elicited cocaine craving

In all, 19 research subjects, with current histories of frequent cocaine use, were exposed to cocaine-related cues to elicit drug craving. We measured the change of occupancy of dopamine at D2-like receptors with positron emission tomography (PET) and inferred a change of intrasynaptic dopamine (endogenous dopamine release), based on the displacement of radiotracer [(11)C]raclopride. Receptor occupancy by dopamine increased significantly in putamen of participants who reported cue-elicited craving compared to those who did not. Further, the intensity of craving was positively correlated with the increase in dopamine receptor occupancy in the putamen. These results provide direct evidence that occupancy of dopamine receptors in human dorsal striatum increased in proportion to subjective craving, presumably because of increased release of intrasynaptic dopamine.

Cognitive processing of drug-related stimuli: the role of memory and attention

Recent studies have investigated the role of attentional biases and memory in alcohol and other drugs of dependence and the relationship between the motivation to use alcohol or other drugs and vigilance for relevant stimuli in alcohol and drug dependence. Based on this research, we describe relationships among motivation, memory, and attentional biases in order to enable better understanding of their multiple and interacting roles in the maintenance and development of alcohol and other drug dependence. We argue that memory and attentional processes are critical in the development and maintenance of addiction processes. Furthermore, we assume that attentional bias is not simply a by-product of an addiction disorder but plays a vital role in its development and maintenance, and it serves to enhance actual drug use. Finally, we predict that the motivation to use alcohol or other drugs will increase vigilance for substance-related stimuli, which in turn can lead to actual use. Future research is needed to ll gaps in our knowledge and lead to a more defined and articulated cognitive-behavioural model of drug dependence.

Toward a model of drug relapse: an assessment of the validity of the reinstatement procedure

BACKGROUND AND RATIONALE

The reinstatement model is widely used to study relapse to drug addiction. However, the model's validity is open to question.

OBJECTIVE

We assess the reinstatement model in terms of criterion and construct validity.

RESEARCH HIGHLIGHTS AND CONCLUSIONS

We find that the reinstatement model has adequate criterion validity in the broad sense of the term, as evidenced by the fact that reinstatement in laboratory animals is induced by conditions reported to provoke relapse in humans. The model's criterion validity in the narrower sense, as a medication screen, seems promising for relapse to heroin, nicotine, and alcohol. For relapse to cocaine, criterion validity has not yet been established primarily because clinical studies have examined medication's effects on reductions in cocaine intake rather than relapse during abstinence. The model's construct validity faces more substantial challenges and is yet to be established, but we argue that some of the criticisms of the model in this regard may have been overstated.

Applications of fMRI in translational medicine and clinical practice

Functional MRI (fMRI) has had a major impact in cognitive neuroscience. fMRI now has a small but growing role in clinical neuroimaging, with initial applications to neurosurgical planning. Current clinical research has emphasized novel concepts for clinicians, such as the role of plasticity in recovery and the maintenance of brain functions in a broad range of diseases. There is a wider potential for clinical fMRI in applications ranging from presymptomatic diagnosis, through drug development and individualization of therapies, to understanding functional brain disorders. Realization of this potential will require changes in the way clinical neuroimaging services are planned and delivered.

Blockade of cue-induced brain activation of abstinent alcoholics by a single administration of amisulpride as measured with fMRI

BACKGROUND

Once alcohol dependence is established, alcohol-associated cues may induce dopamine release in the reward system, which is accompanied by alcohol craving and may lead to relapse. In cocaine addicts, dopamine release in the thalamus was positively correlated with cocaine craving. We tested the effects of the atypical dopamine D(2/3) blocker amisulpride on cue-induced brain activation in a functional magnetic resonance imaging (fMRI) paradigm.

METHODS

Alcohol-associated and neutral pictures were presented in a block design to 10 male abstinent alcoholics (1-3 weeks after detoxification) and 10 healthy men during fMRI. The fMRI scans were acquired before and 2 hours after the oral application of 400 mg amisulpride. Before and after each scan, alcohol craving was measured with visual analogue scales.

RESULTS

Before the application of amisulpride, alcohol versus control cues elicited a higher blood oxygen level-dependent (BOLD) signal in the left frontal and orbitofrontal lobe, left cingulate gyrus, bilateral parietal lobe, and bilateral hippocampus in alcoholics compared with healthy controls. After amisulpride, alcoholics showed a reduced activation in the right thalamus compared with the first scan. Alcoholics no longer showed significant differences in their cue-elicited BOLD response after amisulpride medication compared with medication-free controls. Self-reported craving was not affected by amisulpride medication.

CONCLUSIONS

Amisulpride medication was associated with reduced cue-induced activation of the thalamus, a brain region closely connected with frontostriatal circuits that regulate behavior and may influence relapse risk.

The validity and reliability of a brief measure of cocaine craving

INTRODUCTION

Although craving plays an important role in relapse, there are few brief, valid and reliable instruments to measure the desire to use cocaine in routine clinical practice. The 45-item Cocaine Craving Questionnaire-Now (CCQ-Now) is widely used in research, but its length makes its use in everyday clinical work relatively impractical. This study sought to determine the psychometric properties of the CCQ-Brief, a measure composed of 10 items from the CCQ-Now, in treatment-seeking cocaine abusers.

METHOD

Subjects with cocaine abuse or dependence (n=247) completed the CCQ-Brief, the CCQ-Now, the Voris Cocaine Craving Scale, the Beck Depression Inventory-II, the Beck Anxiety Inventory, and the Addiction Severity Index.

RESULTS

The CCQ-Brief was significantly correlated with the CCQ-Now (r=.85, p<.01), the CCQ-Now with the items in common with the CCQ-Brief removed (r=.78, p<.01), all four subscales of the VCCS (craving intensity: r=.47, p<.01; mood: r=.27, p<.01; energy: r=.30, p<.01; sick feelings: r=.28, p<.01), the BDI-II (r=.39, p<.01), the BAI (r=.35, p<.01) and recent drug use (r=.26, p<.01). The internal consistency of the CCQ-Brief was strong (alpha=.90).

DISCUSSION

The CCQ-Brief is a valid and reliable instrument that can be easily administered as a measure of current cocaine craving.

Long-term behavioural changes after unilateral stereotactic cingulotomy in a case of therapy-resistant alcohol dependence

We report the case of a female patient who had undergone a unilateral stereotactical anterior cingulotomy (AC) 20 years previously because of refractory alcohol dependence. After AC, the drinking behaviour switched from a chronic to an episodic one with fast losses of control accompanied by abnormal oral impulse-control behaviour. Relapses were stress- but not cue-induced and followed by long-term intervals of abstinence. In addition to an intended lesion of the left dorsal anterior cingulate cortex (ACC), MR images showed additional lesions within the left caudate body and the dorsal medial thalamic nucleus. Applying a neuropsychological test battery, we found disturbed divided attention and impaired executive function. From this, we conclude that the complex lesion pattern may contribute to some of the behavioural changes seen in our patient after AC. This hypothesis is supported by the neuropsychological deficits and the fact that the neuronal circuits, impaired by the lesions, are involved in addiction-specific behaviour. This case report further emphasizes the key role of the ACC and its connections in the maintenance of dependent behaviour.

Imaging alcohol cue exposure in alcohol dependence using a PET 15O-H2O paradigm: results from a pilot study

Craving is a commonly used term to describe an intense desire for a substance or behaviour; however, its underlying neurobiology is not fully characterized. We have successfully used a cue exposure paradigm with functional neuro-imaging (H2 15O PET; PET, positron emission tomography) in abstinent opiate addicts. This study showed that salient cue exposure results in activation in the left anterior cingulate/mediofrontal cortex and elicited craving correlated with activity in the left orbitofrontal cortex. We therefore aimed to replicate this study in alcohol dependence to see if a similar pattern of neural activation occurred. We recruited six abstinent alcohol-dependent and six non-dependent subjects who each underwent a 12-run PET scan using H2 15O to measure changes in regional blood flow during exposure to an alcoholic drink or its visually matched non-alcoholic drink. Physiological data and subjective ratings were also recorded. Statistical parametric mapping (SPM99) was used to analyse the PET images. Compared with control subjects, abstinent alcohol-dependent subjects rated their alcohol craving higher at baseline and throughout the study, but there was no significant change in the scores in response to the cues in either group. SPM analysis across all subjects showed significant activation in the occipital cortex in response to the alcohol cue as compared with the neutral one. Analysis of the same regions that were activated in the opiate study, revealed significant increases in signal activation in the left medial prefrontal area, but only in abstinent alcohol-dependent subjects. In conclusion, in abstinent alcohol dependence we suggest that a simple cue exposure paradigm is not sufficiently powerful in functional imaging studies to determine the underlying neurobiology of subjective craving. Comparisons with the finding in opiate dependence suggest a shared region, the anterior cingulate/left medial prefrontal cortex is involved in the cue response in dependent subjects but not controls.

Cue-induced brain activity changes and relapse in cocaine-dependent patients

This study used functional magnetic resonance imaging (fMRI) to examine the association between brain activation during exposure to cocaine-related cues and relapse to drug use in cocaine-dependent (CD) patients. We imaged 17 CD subjects during a 2-week in-patient stay. The subjects then entered a 10-week outpatient placebo-controlled, double-blind randomized clinical trial where urine toxicologies were assessed three times weekly to calculate the treatment effectiveness score (TES). Worse TES correlated with BOLD activation in the left precentral, superior temporal, and posterior cingulate cortices (PCC), and right middle temporal and lingual cortices (R>0.65; P<0.005). The left PCC activation also distinguished eight nonrelapsers (TES above mean and completed treatment) from nine relapsers. Cocaine-free urines were significantly greater in the nonrelapsers (92%) than in the relapsers (66%), who also remained in treatment for an average of only 3.2 weeks. Self-reports of craving during fMRI did not differ between nonrelapsers and relapsers and did not correlate with TES. Relapse to cocaine abuse was associated with increased activation in the sensory association cortex, the motor cortex, and PCC while viewing images of cocaine-related cues. These results suggest that relapse to cocaine abuse is associated with increased brain activation to cocaine cues in sensory, motor, and cognitive-emotional processing areas. This physiological activation was a better predictor of relapse than subjective reports of craving, and may be a useful target for treatment development.

Activation of orbital and medial prefrontal cortex by methylphenidate in cocaine-addicted subjects but not in controls: relevance to addiction

Drugs of abuse are rewarding to addicted and nonaddicted subjects, but they trigger craving and compulsive intake only in addicted subjects. Here, we used positron emission tomography (PET) and [18F] deoxyglucose to compare the brain metabolic responses (marker of brain function) of cocaine-addicted subjects (n = 21) and controls (n = 15) to identify brain regions that are uniquely activated in addicted subjects by intravenous methylphenidate (a drug that cocaine-addicted subjects report to be similar to cocaine). In parallel, we also measured the changes in dopamine (DA) induced by intravenous methylphenidate (using PET and [11C] raclopride) in the striatum and in the thalamus. Metabolic responses between groups differed significantly only in the right medial orbital prefrontal cortex [Brodmann's area (BA) 25 and medial BA 11], where methylphenidate increased metabolism in addicted subjects but decreased metabolism in controls. These changes were associated in all subjects with increased "desire for methylphenidate" and in the addicted subjects with "cocaine craving." In addicted subjects, increases in BA 25 were also associated with mood elevation. Methylphenidate-induced increases in metabolism in the medial orbital prefrontal cortex were associated with its increase of DA in the thalamus but not in the striatum. These findings provide evidence that enhanced sensitivity of BA 25 (region involved with emotional reactivity) and BA 11 (region involved with salience attribution and motivation) in cocaine-addicted subjects may underlie the strong emotional response to the drug and the intense desire to procure it that results in craving and compulsive drug intake. It also suggests that the mesothalamic DA pathway may contribute to these processes.

Update on pathological gambling

Pathological gambling (PG) is a significant public health concern associated with high rates of psychiatric comorbidity and mortality. Although research into the biology of PG is still in an early stage, recent advances in our understanding of motivation, reward, and addiction have provided substantial insight into the possible pathophysiology of this disorder. In addition, over the past 5 years, extraordinary progress has been made in the area of clinical research examining treatments for PG. Although PG is a disabling disorder that continues to represent a clinical challenge for the healthcare professional, our current knowledge of pharmacotherapy and psychosocial interventions offers potentially effective treatment options.

Neuropsychological Performance, Impulsivity, and Comorbid Psychiatric Illness in Patients with Pathological Gambling Undergoing Treatment at the CORE Inpatient Treatment Center

INTRODUCTION

Pathologic gambling is a disorder with features that implicate abnormal functioning in brain regions involved in addiction, mood, anxiety, and impulse control disorders. Our goal was to examine brain function with neurocognitive tasks that target these brain regions in patients with pathologic gambling.

METHODS

Patients were evaluated for comorbid psychiatric disorders, impulsivity, and performance on reversal-learning and reward-based decision-making cognitive tasks.

RESULTS

Patients had higher impulsivity scores and significant deficits on both cognitive tasks compared with controls. All subjects also had comorbid psychiatric disorders, including mood, anxiety, psychotic, and substance abuse.

CONCLUSION

The cognitive deficits and impulsivity are consistent with abnormal activity in orbitofrontal-limbic networks. The high level of comorbidity is consistent with the overall severity in these inpatients undergoing treatment, and adds weight to the concept of a fundamental abnormality in this network.

Neural activity associated with stress-induced cocaine craving: a functional magnetic resonance imaging study

OBJECTIVE

Stress is known to increase cocaine craving and relapse risk in cocaine dependence. Identifying neural activity associated with stress and stress-induced cocaine craving is important in understanding the neurobiology of cocaine craving and relapse.

METHOD

Blood oxygenation level dependent (BOLD) signal changes were assessed in a functional magnetic resonance imaging (fMRI) session with healthy controls and treatment-engaged, abstinent, cocaine-dependent individuals (patients) as they participated in brief guided imagery and recall of three personal stress and three personal neutral situations.

RESULTS

During stress, patients showed significantly less BOLD activation than controls in specific frontal and para-limbic regions, such as the anterior cingulate (AC) region, left hippocampal/parahippocampal region, right fusiform gyrus, and the right postcentral gyrus. On the other hand, patients had increased activity in the caudate and dorsal striatum region during stress, activation that was significantly associated with stress-induced cocaine craving ratings.

CONCLUSIONS

Patients failed to activate AC and related circuits during stress, regions associated with control, and regulation of emotion and distress states. Instead, they exhibited greater craving-related activation in the dorsal striatum, a region related to reward pathways and part of the obsessive-compulsive circuitry. Such functional alterations in stress processing may underlie the stress-related vulnerability to cocaine relapse often observed in cocaine-dependent individuals in early recovery.

Cue-induced brain activity in pathological gamblers

BACKGROUND

Previous studies using functional magnetic resonance imaging (fMRI) have identified differential brain activity in healthy subjects performing gambling tasks and in pathological gambling (PG) subjects when exposed to motivational and emotional predecessors for gambling as well as during gambling or response inhibition tasks. The goal of the present study was to determine if PG subjects exhibit differential brain activity when exposed to visual gambling cues.

METHODS

Ten male DSM-IV-TR PG subjects and 10 matched healthy control subjects underwent fMRI during visual presentations of gambling-related video alternating with video of nature scenes.

RESULTS

Pathological gambling subjects and control subjects exhibited overlap in areas of brain activity in response to the visual gambling cues; however, compared with control subjects, PG subjects exhibited significantly greater activity in the right dorsolateral prefrontal cortex (DLPFC), including the inferior and medial frontal gyri, the right parahippocampal gyrus, and left occipital cortex, including the fusiform gyrus. Pathological gambling subjects also reported a significant increase in mean craving for gambling after the study. Post hoc analyses revealed a dissociation in visual processing stream (dorsal vs. ventral) activation by subject group and cue type.

CONCLUSIONS

These findings may represent a component of cue-induced craving for gambling or conditioned behavior that could underlie pathological gambling.

Abstinence-induced changes in self-report craving correlate with event-related FMRI responses to smoking cues

Drug cues have been shown to activate brain regions involved in attention, motivation, and reward in addicted users. However, as studies have typically measured responses in only one state (ie drug abstinence), it is unclear whether observed activations represent amplification by abstinence or stable responses. Thus, the present study was designed to evaluate the stability of event-related responses to visual drug cues in dependent smokers (n=13) using event-related functional magnetic resonance imaging measures. Imaging was conducted following smoking as usual and following overnight abstinence, and self-reported craving measures were obtained before, during, and after scanning. Analysis of hemodynamic response (HDR) amplitudes in each of 13 regions of interest revealed larger responses to smoking compared to control cues in ventral anterior cingulate gyrus (vACG) and superior frontal gyrus. Responses to smoking cues in these and all other regions revealed no effects of abstinence/satiety, thus supporting the notion that cue-elicited brain responses are relatively stable. However, while the abstinence manipulation did not alter group-level responses to smoking cues, at the individual level, abstinence-induced changes in craving (abstinence minus satiety) were positively correlated with changes in HDR amplitude to smoking cues in frontal regions including left inferior frontal gyrus, left vACG, and bilateral middle frontal gyrus. These results suggest that brain responses to smoking cues, while relatively stable at the group level following short-term abstinence, may be modulated by individual differences in craving in response to abstinence-particularly in regions subserving attention and motivation.

A Functional Magnetic Resonance Imaging (fMRI) Study of Cue-Induced Smoking Craving in Virtual Environments

Smokers who are exposed to smoking-related cues show cardiovascular reactivity and smoking craving compared with their responses to neutral cues, and increased cue reactivity predicts decreased likelihood of successful cessation. Several brain imaging studies suggested four candidate brain regions that might differ in gray matter volumes and densities between smokers and nonsmokers. However, in these studies, smokers were only exposed to smoking-related objects. In our pilot study utilizing a virtual reality (VR) technique, virtual environments (VEs) were more immersive and evoked smoking craving more effectively than traditionally used methods. In this study, we sought to test whether smokers could experience cue-induced smoking craving inside the MRI scanner by using the VR system. The smoking cue reactivity scenario was based in part on our preliminary task and consisted of 2D and 3D (or VE) conditions. The group mean of participants had increased activity in the prefrontal cortex (PFC), left anterior cingulate gyrus (ACC), left supplementary motor area, left uncus, right inferior temporal gyrus, right lingual gyrus, and right precuneus in the 2D condition. Areas of differential activation in the 3D condition were as follows: left superior temporal gyrus, right superior frontal gyrus, and left inferior occipital gyrus in the 3D condition. This finding is consistent with those of previous studies of nicotine craving showing PFC and ACC activation. However, in the 3D condition, the PFC including the superior frontal gyrus as well as the superior temporal gyrus, inferior occipital gyrus, and cerebellum were activated. Therefore, in the 3D condition, participants seemed to have more attention, visual balance, and coordinating movement than in the 2D condition.

Substance use disorders and the orbitofrontal cortex: systematic review of behavioural decision-making and neuroimaging studies

BACKGROUND

Orbitofrontal cortex dysfunctions have been frequently documented in people with substance use disorders. The exact role of this cortical region, however, remains unspecified.

AIMS

To assess the functionality of the orbitofrontal cortex in people with substance use disorders.

METHOD

Reports of studies using behavioural decision-making tasks and/or neuroimaging techniques to investigate orbitofrontal cortex functioning in cases of substance misuse were reviewed. Studies focusing exclusively on tobacco-smoking and gambling were excluded.

RESULTS

Fifty-two research articles were evaluated. Most studies showed significant deficits in decision-making in people with substance use disorders. A consistent finding in the neuroimaging studies was hypoactivity of the orbitofrontal cortex after detoxification. The association between hyperactivity of this region and craving or cue reactivity was not consistent across studies.

CONCLUSIONS

The orbitofrontal cortex has an important role in addictive behaviours. Further studies are needed to elucidate the underlying neuronal substrates of cue reactivity, craving and decision-making, and the implications for treatment and relapse prevention.

Treatment of substance use disorders in schizophrenia: a unifying neurobiological mechanism?

Substance use disorders (SUDs) are highly prevalent and are associated with poor outcomes among individuals with schizophrenia. Integrating treatments for both disorders improves outcomes. Numerous individual pharmacologic and psychosocial treatments have shown effectiveness at reducing substance use in individuals with a primary diagnosis of schizophrenia and co-occurring substance use disorders. Of these treatments, medications such as certain atypical antipsychotics and naltrexone, and psychosocial treatments such as contingency management, seem to be particularly promising. The development and evaluation of psychopharmacologic and psychosocial treatments for SUDs in schizophrenia would benefit from a better understanding of the neurobiological mechanisms underlying the effectiveness of such treatments. Several theories have been put forth to explain the heightened risk for SUDs in schizophrenia. Of these, brain reward circuitry dysfunction, hypothesized to be etiologically important in SUDs, may be an especially salient target for treatments aimed at the reduction of substance use in patients with schizophrenia. We review current pharmacologic and psychosocial treatments for SUDs in schizophrenia, and theoretical mechanisms underlying the increased risk for SUDs in this population. We propose that effective treatments may in part work through the modulation of brain reward circuitry dysfunction.

Contextual cues associated with nicotine administration increase arc mRNA expression in corticolimbic areas of the rat brain

Conditioned responses to cues associated with the administration of drugs of misuse are an impediment to continued abstinence for drug-free addicted individuals. In order to study the neuroanatomical and cellular response of the brain to cues associated with nicotine administration, we conditioned Sprague-Dawley rats to receive an ascending dose regimen of nicotine over 14 days in two distinct non-home cage environments and assessed expression of the early response gene arc in corticolimbic areas in response to the nicotine-associated context. All of the rats received the same dose regimen of nicotine. Three days after the last training day, the rats were exposed to the test environment. The rats that had previously received nicotine exhibited increased motor activity compared with the rats that had received saline in the test environment. After 45 min in the test environment, brains were taken for Northern blotting and in situ hybridization analysis, which revealed an increase in levels of activity-regulated, dendritically localized mRNA for arc in a variety of brain regions (medial and lateral prefrontal cortices, cingulate cortex, primary sensory cortex, sensorimotor cortex, ventral striatum and amygdala). Plasma corticosterone levels were not different between the groups, suggesting that exposure to nicotine cues is insufficient to activate the hypothalamo-pituitary-adrenal axis. Given that Arc plays a direct role in neuronal plasticity and memory consolidation, its induction by nicotine-associated cues in brain regions critical for cognitive and emotional processing suggests that rats may be learning that these cues are no longer necessarily predictive of nicotine administration. Further work will be needed in order to assess the role of arc expression in the extinction of conditioned responses to drug-paired cues.

Neural correlates of high and craving during cocaine self-administration using BOLD fMRI

Modern theories of drug dependence hold the hedonic effects of drug-taking central to understanding the motivation for compulsive drug use. Previous neuroimaging studies have begun to identify brain regions associated with acute drug effects after passive delivery. In this study, a more naturalistic model of cocaine self-administration (SA) was employed in order to identify those sites associated with drug-induced high and craving as measures of reward and motivation. Non-treatment seeking cocaine-dependent subjects chose both when and how often i.v. cocaine administration occurred within a medically supervised SA procedure. Both functional magnetic resonance imaging (fMRI) data and real-time behavioral ratings were acquired during the 1-h SA period. Drug-induced HIGH was found to correlate negatively with activity in limbic, paralimbic, and mesocortical regions including the nucleus accumbens (NAc), inferior frontal/orbitofrontal gyrus (OFC), and anterior cingulate (AC), while CRAVING correlated positively with activity in these regions. This study provides the first evidence in humans that changes in subjective state surrounding cocaine self-administration reflect neural activity of the endogenous reward system.

Experience of emotions in substance abusers exposed to images containing neutral, positive, and negative affective stimuli

There is emerging evidence that suggests emotional processes may be involved in the development of addiction, and that emotional alterations may compromise the effectiveness of treatment approaches in substance abuse. Nonetheless, there is a dearth of studies that have examined the experience of emotions in substance abusers, especially with regard to natural affective stimuli that are motivationally relevant for the normal population. The main aims of this study are: (a) to examine possible differences in the experience of emotions of drug-free substance abusers exposed to images containing motivationally relevant stimuli, with regard to a normal population and (b) to examine possible differences in the experience of emotions of substance abusers depending on their drug of choice. We used 25 images from the International Affective Picture System (IAPS) to elicit different emotional states, and the Self Assessment Manikin (SAM) to record participants' subjective experience on three emotional dimensions: valence, arousal, and dominance. We used bifactorial MANOVA to examine subjective emotional ratings as a function of group, and as a function of the kind of image shown. Results showed a differential emotional profile of substance abusers with regard to healthy controls; and different emotional profiles between abusers of a number of substances. These results suggest the experience of emotions may be significantly altered in substance abusers, and that these alterations may play an important role in drug abuse treatment course and results.

Neural circuits underlying emotional distress in humans

Difficulties in the experiences and regulation of emotional stress have been associated with the development of psychiatric and substance use disorders. This study examined neural circuits underlying emotional distress in healthy volunteers using functional magnetic resonance imaging (fMRI) techniques. Recall of personal nontraumatic, highly stressful life events with script-driven guided imagery was used to induce moderate levels of emotional distress in eight healthy volunteers. Subjects participated in six guided imagery trials (3 separate stress and 3 separate neutral-relaxing scripts each) interspersed by rest periods in a 1.5T scanner. Results indicated significant activation in the medial prefrontal, anterior cingulate, caudate, putamen, thalamus, hippocampus, parahippocampal gyrus, and posterior cingulate regions during emotional distress relative to brain activation during neutral-relaxing imagery. These findings suggest that specific striatal-limbic-prefrontal cortical circuits are involved in the experience and regulation of emotional stress in humans. The study also provides a feasible method to study brain correlates of emotional stress processing in healthy individuals and clinical samples.