Conditional Responding is Impaired in Chronic Alcoholics

Reversal of alcohol dependence-induced deficits in cue-guided behavior via mGluR2/3 signaling in mice

RATIONALE

Alcohol use disorders are associated with deficits in adaptive behavior. While some behavioral impairments that are associated with alcohol use disorders may predate exposure to drugs of abuse, others may result directly from exposure to drugs of abuse, including alcohol. Identifying a causal role for how alcohol exposure leads to these impairments will enable further investigation of the neurobiological mechanisms by which it acts to dysregulate adaptive behavior.

OBJECTIVES

In the present study, we examined the effects of chronic intermittent ethanol exposure (CIE) on the use of reward-paired cues to guide consummatory behaviors in a mouse model, and further, how manipulations of mGluR2/3 signaling-known to be dysregulated after chronic alcohol exposure-may alter the expression of this behavior.

METHODS

Adult male C57B/6J mice were trained to self-administer 10 % ethanol and exposed to CIE via vapor inhalation. After CIE exposure, mice were trained in a Pavlovian task wherein a cue (tone) was paired with the delivery of a 10 % sucrose unconditioned stimulus. The use of the reward-paired cue to guide licking behavior was determined across training. The effect of systemic mGluR2/3 manipulation on discrimination between cue-on and cue-off intervals was assessed by administration of the mGluR2/3 agonist LY379268 or the antagonist LY341495 prior to a testing session.

RESULTS

Exposure to CIE resulted in reductions in discrimination between cue-on and cue-off intervals, with CIE-exposed mice exhibiting significantly lower consummatory behavior during reward-paired cues than air controls. In addition, systemic administration of an mGluR2/3 agonist restored the use of reward-paired cues in CIE-exposed animals without impacting behavior in air controls. Conversely, administration of an mGluR2/3 antagonist mimicked the effects of CIE on cue-guided licking behavior, indicating that mGluR2/3 signaling can bidirectionally regulate the ability to use reward-paired cues to guide behavior.

CONCLUSIONS

Together, these data suggest that chronic ethanol exposure drives impairments in the ability to use reward-paired cues to adaptively regulate behavior and that mGluR2/3 receptors represent a therapeutic target for restoration of these deficits in behavioral control in the alcoholic.

Brain function during cognitive flexibility and white matter integrity in alcohol-dependent patients, problematic drinkers and healthy controls

Cognitive flexibility has been associated with prefrontal white matter (WM) integrity in healthy controls (HCs), showing that lower WM integrity is associated with worse performance. Although both cognitive flexibility and WM integrity have been found to be aberrant in alcohol-dependent (AD) patients, the relationship between the two has never been tested. In this study, we investigated the association between WM tract density and cognitive flexibility in patients with AD (n = 26) and HCs (n = 22). In order to assess the influence of AD severity, we also included a group of problematic drinkers (PrDs; n = 23) who did not meet the AD criteria. Behavioral responses and brain activity during a cognitive flexibility task were measured during functional magnetic resonance imaging. Probabilistic fiber tracking was performed between the dorsolateral prefrontal cortex and the basal ganglia; two crucial regions for task switching. Finally, the task-related functional connectivity between these areas was assessed. There were no significant group differences in the task performance. However, compared with HCs, AD patients and PrDs showed decreased WM integrity and increased prefrontal brain activation during task switching. Evidence is presented for a compensatory mechanism, involving recruitment of additional prefrontal resources in order to compensate for WM and neural function impairments in AD patients and PrDs. Although present in both alcohol groups, the PrDs were more successful in invoking this compensatory mechanism when compared to the AD patients. We propose that this may therefore serve as a protective factor, precluding transition from problematic drinking into alcohol dependence.

Decision making and impulsiveness in abstinent alcohol-dependent people and healthy individuals: a neuropsychological examination

Background

Alcohol dependence is associated with deficits in decision making and increased impulsiveness. Therefore, we compared decision making in abstinent alcohol-dependent people (“abstainers”) and matched healthy individuals (“comparison group”) to determine whether impulsiveness or personality traits play a role in decision making.

Methods

Abstainers (n = 40) were recruited from treatment facilities in and around Munich, Germany, and the comparison group (n = 40) through personal contacts and social media. We assessed decision making with the Iowa Gambling Task (IGT), impulsiveness with the Barratt Impulsiveness Scale (BIS-11) and personality traits with the NEO Five-Factor Inventory (NEO-FFI).

Results

The comparison group performed significantly better in the IGT (mean profit € 159.50, SD 977.92) than the abstainers (mean loss - € 1,400.13, SD 1,362.10; p < .001) and showed significantly less impulsiveness in the BIS-11 (comparison group: mean 56.03, SD 7.80; abstainers: mean 63.55, SD 11.47; p < .001). None of the five personality traits assessed with the NEO-FFI differed significantly between the groups.

Conclusion

The results confirm that abstinent alcohol-dependent people do not perform as well as healthy individuals in decision-making tasks and show greater impulsiveness, but in this study did not affect their decision-making ability.

Habitual alcohol seeking: modeling the transition from casual drinking to addiction

The transition from goal-directed actions to habitual ethanol seeking models the development of addictive behavior that characterizes alcohol use disorders. The progression to habitual ethanol-seeking behavior occurs more rapidly than for natural rewards, suggesting that ethanol may act on habit circuit to drive the loss of behavioral flexibility. This review will highlight recent research that has focused on the formation and expression of habitual ethanol seeking, and the commonalities and distinctions between ethanol and natural reward-seeking habits, with the goal of highlighting important, understudied research areas that we believe will lead toward the development of novel treatment and prevention strategies for uncontrolled drinking.

Widespread and sustained cognitive deficits in alcoholism: a meta-analysis

The cognitive repercussions of alcohol dependence are well documented. However, the literature remains somewhat ambiguous with respect to which distinct cognitive functions are more susceptible to impairment in alcoholism and to how duration of abstinence affects cognitive recovery. Some theories claim alcohol negatively affects specific cognitive functions, while others assert that deficits are more diffuse in nature. This is the first meta-analysis to examine cognition in alcohol abuse/dependence and the duration of abstinence necessary to achieve cognitive recovery. A literature search yielded 62 studies that assessed cognitive dysfunction among alcoholics. Effect size estimates were calculated using the Comprehensive Meta-Analysis V2, for the following 12 cognitive domains: intelligence quotient, verbal fluency/language, speed of processing, working memory, attention, problem solving/executive functions, inhibition/impulsivity, verbal learning, verbal memory, visual learning, visual memory and visuospatial abilities. Within these 12 domains, three effect size estimates were calculated based on abstinence duration. The three groups were partitioned into short- (< 1 month), intermediate- (2 to 12 months) and long- (> 1 year) term abstinence. Findings revealed moderate impairment across 11 cognitive domains during short-term abstinence, with moderate impairment across 10 domains during intermediate term abstinence. Small effect size estimates were found for long-term abstinence. These results suggest significant impairment across multiple cognitive functions remains stable during the first year of abstinence from alcohol. Generally, dysfunction abates by 1 year of sobriety. These findings support the diffuse brain hypothesis and suggest that cognitive dysfunction may linger for up to an average of 1 year post-detoxification from alcohol.

Neuropsychological assessment of impulsive behavior in abstinent alcohol-dependent subjects

OBJECTIVE: Poor impulse control is thought to be one of the characteristics of alcohol addiction. The capacity to remain abstinent may be linked to cognitive bias related to three dimensions of impulsivity: motor, non-planning, and attentional impulsivity. The aim of this study was to evaluate the neuropsychological profile related to these impulsivity dimensions in alcohol-dependent patients within 15 -120 days of abstinence. METHOD: We compared 31 alcohol-dependent patients to 30 matched healthy controls regarding their performances on the Continuous Performance Task, the Iowa Gambling Test, and the Wisconsin Card Sorting Test, each of which is thought to tax primarily one of the three dimensions of impulsivity just outlined. RESULTS: When compared to controls, alcohol-dependent patients presented more commission errors on the Continuous Performance Task; made more disadvantageous choices on the Iowa Gambling Test; and made more perseverative errors on the Wisconsin Card Sorting Test. There was no significant correlation between performance on these tests and the length of abstinence. CONCLUSIONS: These results suggest that deficits related to motor, non-planning and attentional components of impulsivity exist in alcohol-dependent patients, in the period immediately after acute alcohol withdrawal. These results may help guide interventions designed to prevent the risk of relapse in alcohol-abstinent patients.

Impaired stimulus-outcome but preserved stimulus-response shifting in young substance-dependent individuals

Substance dependency has been related to an impairment in executive functions and to a dysfunction of the frontal cortex. In this study we developed two experimental tasks, which are physically identical, to analyze whether substance-dependent individuals are impaired in shifting response patterns (stimulus response links) or preferences (stimulus outcome links). To increase the specificity of the dependent variable, we also used two control tasks to analyze for unspecific performance deficits. We included 35 young subjects with polysubstance abuse (International Classification of Diseases, F19.2 ICD 10 diagnosis, mean age of 22 years, maximum age < 27 years) and 18 normal controls, but for a first step focused on only 22 patients and 15 age-matched controls, because we excluded all patients with an IQ below 100. The results show that the substance-dependent individuals are selectively impaired in shifting object preference (stimulus-outcome links) and not in shifting response patterns. They moreover show a higher general impulsivity as reflected in their faster responses than controls on all tasks except the stimulus-outcome task. In a second step we replicated these results by analyzing the original groups of 35 patients and 18 controls. We argue that substance-dependent subjects show an impairment only on specific executive tasks, and these tasks concern stimulus-outcome link shifting, which has been associated with the functioning of the orbitofrontal cortex, not of the lateral prefrontal cortex.