There are well-established links between impulsivity and alcohol use in humans and other model organisms; however, the etiological nature of these associations remains unclear. This is likely due, in part, to the heterogeneous nature of the construct of impulsivity. Many different measures of impulsivity have been employed in human studies, using both questionnaire and laboratory-based tasks. Animal studies also use multiple tasks to assess the construct of impulsivity. In both human and animal studies, different measures of impulsivity often show little correlation and are differentially related to outcome, suggesting that the impulsivity construct may actually consist of a number of more homogeneous (and potentially more meaningful) subfacets. Here, we provide an overview of the different measures of impulsivity used across human and animal studies, evidence that the construct of impulsivity may be better studied in the context of more meaningful subfacets, and recommendations for how research in this direction may provide for better consilience between human and animal studies of the connection between impulsivity and alcohol use.

The current experiments examined the effects of acute or repeated, intermittent administrations of cocaine on the acquisition and reversal of object discriminations by Vervet monkeys in order to test the hypothesis that cocaine treatment affects performance of tasks that depend upon the functions of the orbitofrontal cortex and amygdala. An acute dose of cocaine (1 mg/kg; 20 min prior to testing) impaired reversal of a previously learned object discrimination but had no effect on acquisition of a novel one. Specific impairments of reversal learning were also observed in monkeys 9 and 30 days after repeated administrations of cocaine (2 or The compulsive drug seeking and taking behavior that is characteristic of drug addiction has recently been attributed to complex, inter-related dysfunctions in neural systems mediating incentive motivation and behavioral regulation (e.g., the striatum, amygdala and ventral frontal cortex; Jentsch and Taylor 1999;Robbins and Everitt 1999; Volkow and Folwer 2000;Berke and Hyman 2000). Several lines of evidence support this hypothesis. First, drug addicts exhibit altered cerebral blood flow and metabolism within the striatum, amygdala and frontal cortex both at baseline and after drug-induced craving (c.f. Volkow and Fowler 2000;London et al. 2000). Second, chronic drug administration affects the neurochemistry and anatomy of these brain regions in animal models (Nestler and Aghajanian 1997;Robinson and Kolb 1997;Wolf 1998;Berke and Hyman 2000; Vandershuren and Kalivas 2000;Robinson et al. 2001 (Post et al. 1976), altered incentive motivation (Shippenberg and Heidbreder 1995;Taylor and Horger 1999;Robbins and Everitt 1999) and impaired cognitive and executive function (Jentsch et al. 1997(Jentsch et al. , 2000Rogers et al. 1999;Robbins and Everitt 1999;Grant et al. 2000;Ornstein et al. 2000) after chronic stimulant drug administration.Because of its important role in decision-making (Bechara et al. 2000) and inhibitory control over pre-potent behavior (Roberts and Wallis 2000), an involvement of ventromedial regions of the frontal cortex in drug abuse has been proposed. In essence, impairments of frontal lobe function are thought to effectively 'un-gate' subcortically-mediated, conditioned tendencies (such as established instrumental responses to obtain and consume drugs), resulting in the compulsive drug seeking and taking that characterize addiction (Jentsch and Taylor 1999). Nevertheless, few studies have directly investigated the long-term consequences of prolonged exposure to addictive drugs on frontal cortex cognitive function, particularly in non-human primates.The aim of the current studies was to directly evaluate the function of the prefrontocortico-amygdalo-striatal system after repeated, intermittent cocaine administrations to monkeys. Using an animal model in which drug treatment (schedule and dosing) and withdrawal can be experimentally controlled, we employed a wellcharacterized behavioral task, the acquisition and reversal of a 3-choice object discrimination. T...

Reconsolidation-the stabilization of a memory after retrieval-is hypothesized to be a critical and distinct component of memory processing, the disruption of which results in memory impairment. In the rat, we found that activation of amygdalar protein kinase A (PKA) was sufficient to enhance memory only when it was retrieved; in contrast, PKA inhibition impaired reconsolidation. This study demonstrates both a selective enhancement and an impairment of memory reconsolidation dependent on amygdalar PKA.

Drug use disorders are often accompanied by deficits in the capacity to efficiently process reward-related information and to monitor, suppress, or override reward-controlled behavior when goals are in conflict with aversive or immediate outcomes. This emerging deficit in behavioral flexibility and impulse control may be a central component of the progression to addiction, as behavior becomes increasingly driven by drugs and drug-associated cues at the expense of more advantageous activities. Understanding how neural mechanisms implicated in impulse control are affected by addictive drugs may therefore prove a useful strategy in the search for new treatment options. Animal models of impulsivity and addiction could make a significant contribution to this endeavor. Here, some of the more common behavioral paradigms used to measure different aspects of impulsivity across species are outlined, and the importance of the response to reward-paired cues in such paradigms is discussed. Naturally occurring differences in forms of impulsivity have been found to be predictive of future drug self-administration, but drug exposure can also increase impulsive responding. Such data are in keeping with the suggestion that impulsivity may contribute to multiple stages within the spiral of addiction. From a neurobiological perspective, converging evidence from rat, monkey, and human studies suggest that compromised functioning within the orbitofrontal cortex may critically contribute to the cognitive sequelae of drug abuse. Changes in gene transcription and protein expression within this region may provide insight into the mechanism underlying drug-induced cortical hypofunction, reflecting new molecular targets for the treatment of uncontrolled drug-seeking and drug-taking behavior.

Drug addiction is a progressive and compulsive disorder, where recurrent craving and relapse to drug seeking occur even after long periods of abstinence. A major contributing factor to relapse is drugassociated cues. Here we review behavioral and pharmacological studies outlining novel methods of effective and persistent reductions in cue-induced relapse behavior in animal models. We focus on extinction and reconsolidation of cue-drug associations as the memory processes that are the most likely targets for interventions. Extinction involves the formation of new inhibitory memories rather than memory erasure; thus, it should be possible to facilitate the extinction of cue-drug memories to reduce relapse. We propose that context-dependency of extinction might be altered by mnemonic agents, thereby enhancing the efficacy of cue-exposure therapy as treatment strategy. In contrast, interfering with memory reconsolidation processes can disrupt the integrity or strength of specific cue-drug memories. Reconsolidation is argued to be a distinct process that occurs over a brief time period after memory is reactivated/retrieved --when the memory becomes labile and vulnerable to disruption. Reconsolidation is thought to be an independent, perhaps opposing, process to extinction and disruption of reconsolidation has recently been shown to directly affect subsequent cue-drug memory retrieval in an animal model of relapse. We hypothesize that a combined approach aimed at both enhancing the consolidation of cue-drug extinction and interfering with the reconsolidation of cue-drug memories will have a greater potential for persistently inhibiting cue-induced relapse than either treatment alone.

Background-Alterations in cellular survival and plasticity are implicated in the neurobiology of depression, based primarily on the characterization of antidepressant efficacy in naïve rodents, rather than on models that capture the debilitating and protracted feelings of anhedonia and loss of motivation that are core features of depression.

A history of exposure to stressors may be a predisposing factor for developing posttraumatic stress disorder (PTSD) after trauma. Extinction of conditioned fear appears to be impaired in PTSD, but the consequences of prior stress or excess glucocorticoid exposure for extinction learning are not known. We report that prior chronic exposure to the stress hormone, corticosterone (CORT), decreases endogenous CORT secretion upon context reexposure and impairs extinction after contextual fear conditioning in rats, while leaving fear memory acquisition and expression intact. Posttraining administration of the glucocorticoid receptor (GR) antagonist, RU38486, partially mimicked prior CORT exposure effects on freezing during fear extinction training. Extinction of conditioned fear is an active learning process thought to involve glutamatergic targets—including specific NMDA and AMPA receptor subunits—in the ventromedial prefrontal cortex (vmPFC), which includes the prelimbic, infralimbic, and medial orbitofrontal cortices. After CORT exposure, decreases in the NMDA receptor NR2B subunit and AMPA receptor subunits, GluR2/3, as well as brain-derived neurotrophic factor, were detected in cortical regions, but not dorsal hippocampus (CA1). Receptor subunit expression levels in the vmPFC correlated with freezing during training. In addition, prior CORT selectively decreased sucrose preference, consistent with established models of anhedonia and with blunted affect in PTSD. Together, these data suggest a cellular mechanism by which chronically elevated glucocorticoid exposure—as may be experienced during repeated exposure to stressors—interferes with the neural systems that modulate behavioral flexibility and may thereby contribute to psychopathological fear states.

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