Functional, structural, and emotional correlates of impaired insight in cocaine addiction

IMPORTANCE

Individuals with cocaine use disorder (CUD) have difficulty monitoring ongoing behavior, possibly stemming from dysfunction of brain regions mediating insight and self-awareness.

OBJECTIVE

To investigate the neural correlates of impaired insight in addiction using a combined functional magnetic resonance imaging and voxel-based morphometry approach.

DESIGN, SETTING, AND PARTICIPANTS

This multimodal imaging study was performed at the Clinical Research Center at Brookhaven National Laboratory. The study included 33 CUD cases and 20 healthy controls.

MAIN OUTCOMES AND MEASURES

Functional magnetic resonance imaging, voxel-based morphometry, Levels of Emotional Awareness Scale, and drug use variables.

RESULTS

Compared with the other 2 study groups, the impaired insight CUD group had lower error-induced rostral anterior cingulate cortex (rACC) activity as associated with more frequent cocaine use, less gray matter within the rACC, and lower Levels of Emotional Awareness Scale scores.

CONCLUSIONS AND RELEVANCE

These results point to rACC functional and structural abnormalities and diminished emotional awareness in a subpopulation of CUD cases characterized by impaired insight. Because the rACC has been implicated in appraising the affective and motivational significance of errors and other types of self-referential processing, functional and structural abnormalities in this region could result in lessened concern (frequently ascribed to minimization and denial) about behavioral outcomes that could potentially culminate in increased drug use. Treatments that target this CUD subgroup could focus on enhancing the salience of errors (eg, lapses).

Common and distinct neural targets of treatment: changing brain function in substance addiction

Neuroimaging offers an opportunity to examine the neurobiological effects of therapeutic interventions for human drug addiction. Using activation likelihood estimation, the aim of the current meta-analysis was to quantitatively summarize functional neuroimaging studies of pharmacological and cognitive-based interventions for drug addiction, with an emphasis on their common and distinct neural targets. More exploratory analyses also contrasted subgroups of studies based on specific study and sample characteristics. The ventral striatum, a region implicated in reward, motivation, and craving, and the inferior frontal gyrus and orbitofrontal cortex, regions involved in inhibitory control and goal-directed behavior, were identified as common targets of pharmacological and cognitive-based interventions; these regions were observed when the analysis was limited to only studies that used established or efficacious interventions, and across imaging paradigms and types of addictions. Consistent with theoretical models, cognitive-based interventions were additionally more likely to activate the anterior cingulate cortex, middle frontal gyrus, and precuneus, implicated in self-referential processing, cognitive control, and attention. These results suggest that therapeutic interventions for addiction may target the brain structures that are altered across addictions and identify potential neurobiological mechanisms by which the tandem use of pharmacological and cognitive-based interventions may yield synergistic or complementary effects. These findings could inform the selection of novel functional targets in future treatment development for this difficult-to-treat disorder.

Effects of methylphenidate on resting-state functional connectivity of the mesocorticolimbic dopamine pathways in cocaine addiction

IMPORTANCE

Cocaine addiction is associated with altered resting-state functional connectivity among regions of the mesocorticolimbic dopamine pathways. Methylphenidate hydrochloride, an indirect dopamine agonist, normalizes task-related regional brain activity and associated behavior in cocaine users; however, the neural systems-level effects of methylphenidate in this population have not yet been described.

OBJECTIVE

To use resting-state functional magnetic resonance imaging to examine changes in mesocorticolimbic connectivity with methylphenidate and how connectivity of affected pathways relates to severity of cocaine addiction.

DESIGN

Randomized, placebo-controlled, before-after, crossover study.

SETTING

Clinical research center.

PARTICIPANTS

Eighteen nonabstaining individuals with cocaine use disorders.

INTERVENTIONS

Single doses of oral methylphenidate (20 mg) or placebo were administered at each of 2 study sessions. At each session, resting scans were acquired twice: immediately after drug administration (before the onset of effects [baseline]) and 120 minutes later (within the window of peak effects).

MAIN OUTCOMES AND MEASURES

Functional connectivity strength was evaluated using a seed voxel correlation approach. Changes in this measure were examined to characterize the neural systems-level effects of methylphenidate; severity of cocaine addiction was assessed by interview and questionnaire.

RESULTS

Short-term methylphenidate administration reduced an abnormally strong connectivity of the ventral striatum with the dorsal striatum (putamen/globus pallidus), and lower connectivity between these regions during placebo administration uniquely correlated with less severe addiction. In contrast, methylphenidate strengthened several corticolimbic and corticocortical connections.

CONCLUSIONS AND RELEVANCE

These findings help elucidate the neural systems-level effects of methylphenidate and suggest that short-term methylphenidate can, at least transiently, remodel abnormal circuitry relevant to the pathophysiologic characteristics of cocaine addiction. In particular, the effects of methylphenidate within striatal and cortical pathways constitute a potentially viable mechanism by which methylphenidate could facilitate control of behavior in cocaine addiction.

Choice to view cocaine images predicts concurrent and prospective drug use in cocaine addiction

BACKGROUND

Identifying variables that predict drug use in treatment-seeking drug addicted individuals is a crucial research and therapeutic goal. This study tested the hypothesis that choice to view cocaine images is associated with concurrent and prospective drug use in cocaine addiction.

METHODS

To establish choice-concurrent drug use associations, 71 cocaine addicted subjects (43 current users and 28 treatment seekers) provided data on (A) choice to view cocaine images and affectively pleasant, unpleasant, and neutral images [collected under explicit contingencies (when choice was made between two fully visible side-by-side images) and under more probabilistic contingencies (when choice was made between pictures hidden under flipped-over cards)]; and (B) past-month cocaine and other drug use. To establish choice-prospective drug use associations, 20 of these treatment-seeking subjects were followed over the next 6 months.

RESULTS

Baseline cocaine-related picture choice as measured by both tasks positively correlated with subjects' concurrent cocaine and other drug use as driven by the actively-using subjects. In a subsequent multiple regression analysis, choice to view cocaine images as compared with affectively pleasant images (under probabilistic contingencies) was the only predictor that continued to be significantly associated with drug use. Importantly, this same baseline cocaine>pleasant probabilistic choice also predicted the number of days drugs were used (cocaine, alcohol, and marijuana) over the next 6 months.

CONCLUSIONS

Simulated cocaine choice - especially when probabilistic and when compared with other positive reinforcers - may provide a valid laboratory marker of current and future drug use in cocaine addiction.

Association between dopamine D4 receptor polymorphism and age related changes in brain glucose metabolism

Aging is associated with reductions in brain glucose metabolism in some cortical and subcortical regions, but the rate of decrease varies significantly between individuals, likely reflecting genetic and environmental factors and their interactions. Here we test the hypothesis that the variant of the dopamine receptor D4 (DRD4) gene (VNTR in exon 3), which has been associated with novelty seeking and sensitivity to environmental stimuli (negative and positive) including the beneficial effects of physical activity on longevity, influence the effects of aging on the human brain. We used positron emission tomography (PET) and [(18)F]fluoro-D-glucose ((18)FDG) to measure brain glucose metabolism (marker of brain function) under baseline conditions (no stimulation) in 82 healthy individuals (age range 22-55 years). We determined their DRD4 genotype and found an interaction with age: individuals who did not carry the 7-repeat allele (7R-, n = 53) had a significant (p<0.0001) negative association between age and relative glucose metabolism (normalized to whole brain glucose metabolism) in frontal (r = -0.52), temporal (r = -0.51) and striatal regions (r = -0.47, p<0.001); such that older individuals had lower metabolism than younger ones. In contrast, for carriers of the 7R allele (7R+ n = 29), these correlations with age were not significant and they only showed a positive association with cerebellar glucose metabolism (r = +0.55; p = 0.002). Regression slopes of regional brain glucose metabolism with age differed significantly between the 7R+ and 7R- groups in cerebellum, inferior temporal cortex and striatum. These results provide evidence that the DRD4 genotype might modulate the associations between regional brain glucose metabolism and age and that the carriers of the 7R allele appear to be less sensitive to the effects of age on brain glucose metabolism.

Methylphenidate enhances executive function and optimizes prefrontal function in both health and cocaine addiction

Previous studies have suggested dopamine to be involved in error monitoring/processing, possibly through impact on reinforcement learning. The current study tested whether methylphenidate (MPH), an indirect dopamine agonist, modulates brain and behavioral responses to error, and whether such modulation is more pronounced in cocaine-addicted individuals, in whom dopamine neurotransmission is disrupted. After receiving oral MPH (20 mg) or placebo (counterbalanced), 15 healthy human volunteers and 16 cocaine-addicted individuals completed a task of executive function (the Stroop color word) during functional magnetic resonance imaging (fMRI). During MPH, despite not showing differences on percent accuracy and reaction time, all subjects committed fewer total errors and slowed down more after committing errors, suggestive of more careful responding. In parallel, during MPH all subjects showed reduced dorsal anterior cingulate cortex response to the fMRI contrast error>correct. In the cocaine subjects only, MPH also reduced error>correct activity in the dorsolateral prefrontal cortex (controls instead showed lower error>correct response in this region during placebo). Taken together, MPH modulated dopaminergically innervated prefrontal cortical areas involved in error-related processing, and such modulation was accentuated in the cocaine subjects. These results are consistent with a dopaminergic contribution to error-related processing during a cognitive control task.

Psychophysiological prediction of choice: relevance to insight and drug addiction

An important goal of addiction research and treatment is to predict behavioural responses to drug-related stimuli. This goal is especially important for patients with impaired insight, which can interfere with therapeutic interventions and potentially invalidate self-report questionnaires. This research tested (i) whether event-related potentials, specifically the late positive potential, predict choice to view cocaine images in cocaine addiction; and (ii) whether such behaviour prediction differs by insight (operationalized in this study as self-awareness of image choice). Fifty-nine cocaine abusers and 32 healthy controls provided data for the following laboratory components that were completed in a fixed-sequence (to establish prediction): (i) event-related potential recordings while passively viewing pleasant, unpleasant, neutral and cocaine images, during which early (400-1000 ms) and late (1000-2000 ms) window late positive potentials were collected; (ii) self-reported arousal ratings for each picture; and (iii) two previously validated tasks: one to assess choice for viewing these same images, and the other to group cocaine abusers by insight. Results showed that pleasant-related late positive potentials and arousal ratings predicted pleasant choice (the choice to view pleasant pictures) in all subjects, validating the method. In the cocaine abusers, the predictive ability of the late positive potentials and arousal ratings depended on insight. Cocaine-related late positive potentials better predicted cocaine image choice in cocaine abusers with impaired insight. Another emotion-relevant event-related potential component (the early posterior negativity) did not show these results, indicating specificity of the late positive potential. In contrast, arousal ratings better predicted respective cocaine image choice (and actual cocaine use severity) in cocaine abusers with intact insight. Taken together, the late positive potential could serve as a biomarker to help predict drug-related choice--and possibly associated behaviours (e.g. drug seeking in natural settings, relapse after treatment)--when insight (and self-report) is compromised.

Enhanced midbrain response at 6-month follow-up in cocaine addiction, association with reduced drug-related choice

Drug addiction is characterized by dysregulated dopamine neurotransmission. Although dopamine functioning appears to partially recover with abstinence, the specific regions that recover and potential impact on drug seeking remain to be determined. Here we used functional magnetic resonance imaging (fMRI) to study an ecologically valid sample of 15 treatment-seeking cocaine addicted individuals at baseline and 6-month follow-up. At both study sessions, we collected fMRI scans during performance of a drug Stroop task, clinical self-report measures of addiction severity and behavioral measures of cocaine seeking (simulated cocaine choice); actual drug use in between the two study sessions was also monitored. At 6-month follow-up (compared with baseline), we predicted functional enhancement of dopaminergically innervated brain regions, relevant to the behavioral responsiveness toward salient stimuli. Consistent with predictions, whole-brain analyses revealed responses in the midbrain (encompassing the ventral tegmental area/substantia nigra complex) and thalamus (encompassing the mediodorsal nucleus) that were higher (and more positively correlated) at follow-up than baseline. Increased midbrain activity from baseline to follow-up correlated with reduced simulated cocaine choice, indicating that heightened midbrain activations in this context may be marking lower approach motivation for cocaine. Normalization of midbrain function at follow-up was also suggested by exploratory comparisons with active cocaine users and healthy controls (who were assessed only at baseline). Enhanced self-control at follow-up was suggested by a trend for the commonly hypoactive dorsal anterior cingulate cortex to increase response during a drug-related context. Together, these results suggest that fMRI could be useful in sensitively tracking follow-up outcomes in drug addiction.

Can a single brain region predict a disorder?

We perform prediction of diverse disorders (Cocaine Use, Schizophrenia and Alzheimers disease) in unseen subjects from brain fMRI. First, we show that for multi-subject prediction of simple cognitive states (e.g. motor vs. calculation and reading), voxels-as-features methods produce clusters that are similar for different leave-one-subject-out folds; while for group classification (e.g. cocaine addicted vs. control subjects), voxels are scattered and less stable. Therefore, we chose to use a single region per experimental condition and a majority vote classifier. Interestingly, our method outperforms state-of-the-art techniques. Our method can integrate multiple experimental conditions and successfully predict disorders in unseen subjects (leave-one-subjectout generalization accuracy: 89.3% and 90.9% for Cocaine Use, 96.4% for Schizophrenia and 81.5% for Alzheimers disease). Our experimental results not only span diverse disorders, but also different experimental designs (block design and event related tasks), facilities, magnetic fields (1.5Tesla, 3Tesla, 4Tesla) and speed of acquisition (interscan interval from 1600ms to 3500ms). We further argue that our method produces a meaningful low dimensional representation that retains discriminability.

Sensitivity to monetary reward is most severely compromised in recently abstaining cocaine addicted individuals: a cross-sectional ERP study

Recent studies suggest that drug-addicted individuals have a dampened cortical response to non-drug rewards. However, it remains unclear whether recency of drug use impacts this impairment. Therefore, in this event-related potential study, recency of cocaine use was objectively determined by measuring cocaine in urine on study day. Thirty-five individuals with current cocaine use disorder [CUD: 21 testing positive (CUD+) and 14 testing negative (CUD-) for cocaine in urine] and 23 healthy controls completed a sustained attention task with graded monetary incentives (0¢, 1¢ and 45¢). Unlike in controls, in both CUD subgroups P300 amplitude was not modulated by the varying amounts of money and the CUD- showed the most severe impairment as documented by the lowest P300 amplitudes and task accuracy. Moreover, while recency of drug use was associated with better accuracy and higher P300 amplitudes, chronic drug use was associated with lower sensitivity to money. These results extend our previous findings of decreased sustained sensitivity to monetary reward in CUD+ to recently abstaining individuals, where level of impairment was most severe. Taken together, these results support the self-medication hypothesis, where CUD may be self-administering cocaine to avoid or compensate for underlying cognitive and emotional difficulties albeit with a long-term detrimental effect on sensitivity to non-drug reward.

Structural and behavioral correlates of abnormal encoding of money value in the sensorimotor striatum in cocaine addiction

Abnormalities in frontostriatal systems are thought to be central to the pathophysiology of addiction, and may underlie the maladaptive processing of the highly generalizable reinforcer, money. Although abnormal frontostriatal structure and function have been observed in individuals addicted to cocaine, it is less clear how individual variability in brain structure is associated with brain function to influence behavior. Our objective was to examine frontostriatal structure and neural processing of money value in chronic cocaine users and closely matched healthy controls. A reward task that manipulated different levels of money was used to isolate neural activity associated with money value. Gray matter volume measures were used to assess frontostriatal structure. Our results indicated that cocaine users had an abnormal money value signal in the sensorimotor striatum (right putamen/globus pallidus) that was negatively associated with accuracy adjustments to money and was more pronounced in individuals with more severe use. In parallel, group differences were also observed in both the function and gray matter volume of the ventromedial prefrontal cortex; in the cocaine users, the former was directly associated with response to money in the striatum. These results provide strong evidence for abnormalities in the neural mechanisms of valuation in addiction and link these functional abnormalities with deficits in brain structure. In addition, as value signals represent acquired associations, their abnormal processing in the sensorimotor striatum, a region centrally implicated in habit formation, could signal disadvantageous associative learning in cocaine addiction.

Repeat variation in the human PER2 gene as a new genetic marker associated with cocaine addiction and brain dopamine D2 receptor availability

Low dopamine D2 receptor (D2R) levels in the striatum are consistently reported in cocaine abusers; inter-individual variations in the degree of the decrease suggest a modulating effect of genetic makeup on vulnerability to addiction. The PER2 (Period 2) gene belongs to the clock genes family of circadian regulators; circadian oscillations of PER2 expression in the striatum was modulated by dopamine through D2Rs. Aberrant periodicity of PER2 contributes to the incidence and severity of various brain disorders, including drug addiction. Here we report a newly identified variable number tandem repeat (VNTR) polymorphism in the human PER2 gene (VNTR in the third intron). We found significant differences in the VNTR alleles prevalence across ethnic groups so that the major allele (4 repeats (4R)) is over-represented in non-African population (4R homozygosity is 88%), but not in African Americans (homozygosity 51%). We also detected a biased PER2 genotype distribution among healthy controls and cocaine-addicted individuals. In African Americans, the proportion of 4R/three repeat (3R) carriers in healthy controls is much lower than that in cocaine abusers (23% vs 39%, P=0.004), whereas among non-Africans most 3R/4R heterozygotes are healthy controls (10.5% vs 2.5%, P=0.04). Analysis of striatal D2R availability measured with positron emission tomography and [(11)C]raclopride revealed higher levels of D2R in carriers of 4R/4R genotype (P<0.01). Taken together, these results provide preliminary evidence for the role of the PER2 gene in regulating striatal D2R availability in the human brain and in vulnerability for cocaine addiction.

Neuroimaging for drug addiction and related behaviors

In this review, we highlight the role of neuroimaging techniques in studying the emotional and cognitive-behavioral components of the addiction syndrome by focusing on the neural substrates subserving them. The phenomenology of drug addiction can be characterized by a recurrent pattern of subjective experiences that includes drug intoxication, craving, bingeing, and withdrawal with the cycle culminating in a persistent preoccupation with obtaining, consuming, and recovering from the drug. In the past two decades, imaging studies of drug addiction have demonstrated deficits in brain circuits related to reward and impulsivity. The current review focuses on studies employing positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and electroencephalography (EEG) to investigate these behaviors in drug-addicted human populations. We begin with a brief account of drug addiction followed by a technical account of each of these imaging modalities. We then discuss how these techniques have uniquely contributed to a deeper understanding of addictive behaviors.

Structural integrity of the prefrontal cortex modulates electrocortical sensitivity to reward

The P300 is a known ERP component assessing stimulus value, including the value of a monetary reward. In parallel, the incentive value of reinforcers relies on the PFC, a major cortical projection region of the mesocortical reward pathway. Here we show a significant positive correlation between P300 response to money (vs. no money) with PFC gray matter volume in the OFC, ACC, and dorsolateral and ventrolateral PFC in healthy control participants. In contrast, individuals with cocaine use disorders showed compromises in both P300 sensitivity to money and PFC gray matter volume in the ventrolateral PFC and OFC and their interdependence. These results document for the first time the importance of gray matter structural integrity of subregions of PFC to the reward-modulated P300 response.

Motivation deficit in ADHD is associated with dysfunction of the dopamine reward pathway

Attention-deficit hyperactivity disorder (ADHD) is typically characterized as a disorder of inattention and hyperactivity/impulsivity but there is increasing evidence of deficits in motivation. Using positron emission tomography (PET), we showed decreased function in the brain dopamine reward pathway in adults with ADHD, which, we hypothesized, could underlie the motivation deficits in this disorder. To evaluate this hypothesis, we performed secondary analyses to assess the correlation between the PET measures of dopamine D2/D3 receptor and dopamine transporter availability (obtained with [(11)C]raclopride and [(11)C]cocaine, respectively) in the dopamine reward pathway (midbrain and nucleus accumbens) and a surrogate measure of trait motivation (assessed using the Achievement scale on the Multidimensional Personality Questionnaire or MPQ) in 45 ADHD participants and 41 controls. The Achievement scale was lower in ADHD participants than in controls (11±5 vs 14±3, P<0.001) and was significantly correlated with D2/D3 receptors (accumbens: r=0.39, P<0.008; midbrain: r=0.41, P<0.005) and transporters (accumbens: r=0.35, P<0.02) in ADHD participants, but not in controls. ADHD participants also had lower values in the Constraint factor and higher values in the Negative Emotionality factor of the MPQ but did not differ in the Positive Emotionality factor-and none of these were correlated with the dopamine measures. In ADHD participants, scores in the Achievement scale were also negatively correlated with symptoms of inattention (CAARS A, E and SWAN I). These findings provide evidence that disruption of the dopamine reward pathway is associated with motivation deficits in ADHD adults, which may contribute to attention deficits and supports the use of therapeutic interventions to enhance motivation in ADHD.

Gene x disease interaction on orbitofrontal gray matter in cocaine addiction

CONTEXT

Long-term cocaine use has been associated with structural deficits in brain regions having dopamine-receptive neurons. However, the concomitant use of other drugs and common genetic variability in monoamine regulation present additional structural variability.

OBJECTIVE

To examine variations in gray matter volume (GMV) as a function of lifetime drug use and the genotype of the monoamine oxidase A gene, MAOA, in men with cocaine use disorders (CUD) and healthy male controls.

DESIGN

Cross-sectional comparison.

SETTING

Clinical Research Center at Brookhaven National Laboratory.

PATIENTS

Forty individuals with CUD and 42 controls who underwent magnetic resonance imaging to assess GMV and were genotyped for the MAOA polymorphism (categorized as high- and low-repeat alleles).

MAIN OUTCOME MEASURES

The impact of cocaine addiction on GMV, tested by (1) comparing the CUD group with controls, (2) testing diagnosis × MAOA interactions, and (3) correlating GMV with lifetime cocaine, alcohol, and cigarette smoking, and testing their unique contribution to GMV beyond other factors.

RESULTS

(1) Individuals with CUD had reductions in GMV in the orbitofrontal, dorsolateral prefrontal, and temporal cortex and the hippocampus compared with controls. (2) The orbitofrontal cortex reductions were uniquely driven by CUD with low- MAOA genotype and by lifetime cocaine use. (3) The GMV in the dorsolateral prefrontal cortex and hippocampus was driven by lifetime alcohol use beyond the genotype and other pertinent variables.

CONCLUSIONS

Long-term cocaine users with the low-repeat MAOA allele have enhanced sensitivity to gray matter loss, specifically in the orbitofrontal cortex, indicating that this genotype may exacerbate the deleterious effects of cocaine in the brain. In addition, long-term alcohol use is a major contributor to gray matter loss in the dorsolateral prefrontal cortex and hippocampus, and is likely to further impair executive function and learning in cocaine addiction.

Addiction: pulling at the neural threads of social behaviors

Addiction coopts the brain's neuronal circuits necessary for insight, reward, motivation, and social behaviors. This functional overlap results in addicted individuals making poor choices despite awareness of the negative consequences; it explains why previously rewarding life situations and the threat of judicial punishment cannot stop drug taking and why a medical rather than a criminal approach is more effective in curtailing addiction.

Motivated attention to cocaine and emotional cues in abstinent and current cocaine users--an ERP study

Event-related potentials (ERPs) are a direct measure of neural activity and are ideally suited to study the time-course of attentional engagement with emotional and drug-related stimuli in addiction. In particular, the late positive potential (LPP) appears to be enhanced following cocaine-related compared with neutral stimuli in human participants with cocaine use disorders (CUD). However, previous studies have not directly compared cocaine-related with emotional stimuli while examining potential differences between abstinent and current cocaine users. The present study examined ERPs in 55 CUD (27 abstinent and 28 current users) and 29 matched healthy controls while they passively viewed pleasant, unpleasant, neutral and cocaine-related pictures. To examine the time-course of attention to these stimuli, we analysed both an early and later window in the LPP as well as the early posterior negativity (EPN), established in assessing motivated attention. Cocaine pictures elicited increased electrocortical measures of motivated attention in ways similar to affectively pleasant and unpleasant pictures in all CUD, an effect that was no longer discernible during the late LPP window for the current users. This group also exhibited deficient processing of the other emotional stimuli (early LPP window - pleasant pictures; late LPP window - pleasant and unpleasant pictures). Results were unique to the LPP and not EPN. Taken together, results support a relatively early attention bias to cocaine stimuli in cocaine-addicted individuals, further suggesting that recent cocaine use decreases such attention bias during later stages of processing but at the expense of deficient processing of other emotional stimuli.

A pattern of perseveration in cocaine addiction may reveal neurocognitive processes implicit in the Wisconsin Card Sorting Test

The ability to adapt behavior in a changing environment is necessary for humans to achieve their goals and can be measured in the lab with tests of rule-based switching. Disease models, such as cocaine addiction, have revealed that alterations in dopamine interfere with adaptive set switching, culminating in perseveration. We explore perseverative behavior in individuals with cocaine use disorders (CUD) and healthy controls (CON) during performance of the Wisconsin Card Sorting Test (WCST) (N=107 in each group). By examining perseverative errors within each of the 6 blocks of the WCST, we uniquely test two forms of set switching that are differentiated by either the presence (extradimensional set shifting (EDS) - first 3 blocks) or absence (task-set switching - last 3 blocks) of new contingency learning. We also explore relationships between perseveration and select cognitive and drug use factors including verbal learning and memory, trait inhibitory control, motivational state, and urine status for cocaine (in CUD). Results indicate greater impairment for CUD than CON on the WCST, even in higher performing CUD who completed all 6 blocks of the WCST. Block by block analysis conducted on completers' scores indicate a tendency for greater perseveration in CUD than CON but only during the first task-set switch; no such deficits were observed during EDS. This task-set switching impairment was modestly associated with two indices of immediate recall (r=-.32, -.29) and urine status for cocaine [t (134)=2.3, p<.03]. By distinguishing these two forms of switching on the WCST, the current study reveals a neurocognitive context (i.e. initial stage of task-set switching) implicit in the WCST that possibly relies upon intact dopaminergic function, but that is impaired in CUD, as associated with worse recall and possibly withdrawal from cocaine. Future studies should investigate whether dopaminergically innervated pathways alone, or in combination with other monoamines, underlie this implicit neurocognitive processes in the WCST.

Reduced metabolism in brain "control networks" following cocaine-cues exposure in female cocaine abusers

Objective

Gender differences in vulnerability for cocaine addiction have been reported. Though the mechanisms are not understood, here we hypothesize that gender differences in reactivity to conditioned-cues, which contributes to relapse, are involved.

Method

To test this we compared brain metabolism (using PET and ¹⁸FDG) between female (n = 10) and male (n = 16) active cocaine abusers when they watched a neutral video (nature scenes) versus a cocaine-cues video.

Results

Self-reports of craving increased with the cocaine-cue video but responses did not differ between genders. In contrast, changes in whole brain metabolism with cocaine-cues differed by gender (p<0.05); females significantly decreased metabolism (−8.6%±10) whereas males tended to increase it (+5.5%±18). SPM analysis (Cocaine-cues vs Neutral) in females revealed decreases in frontal, cingulate and parietal cortices, thalamus and midbrain (p<0.001) whereas males showed increases in right inferior frontal gyrus (BA 44/45) (only at p<0.005). The gender-cue interaction showed greater decrements with Cocaine-cues in females than males (p<0.001) in frontal (BA 8, 9, 10), anterior cingulate (BA 24, 32), posterior cingulate (BA 23, 31), inferior parietal (BA 40) and thalamus (dorsomedial nucleus).

Conclusions

Females showed greater brain reactivity to cocaine-cues than males but no differences in craving, suggesting that there may be gender differences in response to cues that are not linked with craving but could affect subsequent drug use. Specifically deactivation of brain regions from “control networks” (prefrontal, cingulate, inferior parietal, thalamus) in females could increase their vulnerability to relapse since it would interfere with executive function (cognitive inhibition). This highlights the importance of gender tailored interventions for cocaine addiction.

Induced magnetic force in human heads exposed to 4 T MRI

PURPOSE

To map the distribution of the magnetic force induced in the human head during magnetic resonance imaging (MRI) at 4 T for a large group of healthy volunteers.

MATERIALS AND METHODS

The magnetic field distribution in the head of 100 men and 18 women was mapped using phase mapping techniques. Statistical parametric mapping methods using a family-wise error (FWE) corrected threshold P < 0.05 and region-of-interest analyses were used to assess the significance of the results.

RESULTS

Eyeballs, orbitofrontal and temporal cortices, subcallosal gyrus, anterior cingulate, midbrain, and brainstem (pons) are the brain regions most susceptible to magnetic force. The strength of the magnetic force density in the head was lower than 11.5 +/- 5.3 N/m(3) (right eyeball). The strength of the magnetic force density induced in occipital cortex varied linearly with the x-rotation (pitch) angle.

CONCLUSION

We found that the induced magnetic force is highly significant in the eyeballs, orbitofrontal and temporal cortices, subcallosal gyrus, anterior cingulate as well as midbrain and brainstem (pons), regardless of subjects' age or gender. The maximum induced magnetic force was 6 x 10(5) times weaker than the gravitational force; thus, biological effects of the magnetic force during imaging are not expected to be significant.

Simultaneous TMS-fMRI of the Visual Cortex Reveals Functional Network, Even in Absence of Phosphene Sensation

Phosphene sensation is commonly used to measure cortical excitability during transcranial magnetic stimulation (TMS) of the occipital cortex. However, some individuals lack this perception, and the reason for it is still unknown. In this work, we used functional magnetic resonance imaging (fMRI) to detect brain activation during local TMS of the occipital cortex in twelve healthy subjects. We found that TMS modulated brain activity in areas connected to the stimulation site, even in people unable to see phosphene. However, we observed a trend for a lower blood-oxygenation-level dependent (BOLD) signal, and smaller brain-activation clusters near the stimulated site than in the interconnected brain areas, suggesting that TMS pulse is more effective downstream than at its application site. Furthermore, we noted prominent differences in brain activation/deactivation patterns between subjects who perceived phosphene and those who did not, implying a functional distinction in their neuronal networks that might explain the origin of differences in phosphene generation.

Striatal dopamine D2 receptor availability predicts the thalamic and medial prefrontal responses to reward in cocaine abusers three years later

Low levels of dopamine (DA) D2 receptor availability at a resting baseline have been previously reported in drug addicted individuals and have been associated with reduced ventral and dorsal prefrontal metabolism. The reduction in DA D2 receptor availability along with the reduced ventral frontal metabolism is thought to underlie compromised sensitivity to nondrug reward, a core characteristic of drug addiction. We therefore hypothesized that variability in DA D2 receptor availability at baseline will covary with dynamic responses to monetary reward in addicted individuals. Striatal DA D2 receptor availability was measured with [(11)C]raclopride and positron emission tomography and response to monetary reward was measured (an average of three years later) with functional magnetic resonance imaging in seven cocaine-addicted individuals. Results show that low DA D2 receptor availability in the dorsal striatum was associated with decreased thalamic response to monetary reward; while low availability in ventral striatum was associated with increased medial prefrontal (Brodmann Area 6/8/32) response to monetary reward. These preliminary results, that need to be replicated in larger sample sizes and validated with healthy controls, suggest that resting striatal DA D2 receptor availability predicts variability in functional responses to a nondrug reinforcer (money) in prefrontal cortex, implicated in behavioral monitoring, and in thalamus, implicated in conditioned responses and expectation, in cocaine-addicted individuals.

Disrupted functional connectivity with dopaminergic midbrain in cocaine abusers

Background

Chronic cocaine use is associated with disrupted dopaminergic neurotransmission but how this disruption affects overall brain function (other than reward/motivation) is yet to be fully investigated. Here we test the hypothesis that cocaine addicted subjects will have disrupted functional connectivity between the midbrain (where dopamine neurons are located) and cortical and subcortical brain regions during the performance of a sustained attention task.

Methodology/Principal Findings

We measured brain activation and functional connectivity with fMRI in 20 cocaine abusers and 20 matched controls. When compared to controls, cocaine abusers had lower positive functional connectivity of midbrain with thalamus, cerebellum, and rostral cingulate, and this was associated with decreased activation in thalamus and cerebellum and enhanced deactivation in rostral cingulate.

Conclusions/Significance

These findings suggest that decreased functional connectivity of the midbrain interferes with the activation and deactivation signals associated with sustained attention in cocaine addicts.