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Drug addiction is increasingly viewed as the endpoint of a series of transitions from initial drug use--when a drug is voluntarily taken because it has reinforcing, often hedonic, effects--through loss of control over this behavior, such that it becomes habitual and ultimately compulsive. Here we discuss evidence that these transitions depend on(More)
Emotions are multifaceted, but a key aspect of emotion involves the assessment of the value of environmental stimuli. This article reviews the many psychological representations, including representations of stimulus value, which are formed in the brain during Pavlovian and instrumental conditioning tasks. These representations may be related directly to(More)
Stimulant addiction is often linked to excessive risk taking, sensation seeking, and impulsivity, but in ways that are poorly understood. We report here that a form of impulsivity in rats predicts high rates of intravenous cocaine self-administration and is associated with changes in dopamine (DA) function before drug exposure. Using positron emission(More)
NMDA receptors are important for the acquisition, reconsolidation, and extinction of memories. NMDA receptor antagonists impair these memory processes, whereas the partial agonist D-cycloserine (DCS) potentiates both learning and extinction. Here, we used DCS and the noncompetitive NMDA receptor antagonist(More)
We have investigated the neurochemical mechanisms of memory reconsolidation and, in particular, the functional requirement for intracellular mechanisms initiated by beta-adrenergic signaling. We show that propranolol, given in conjunction with a memory reactivation session, can specifically disrupt the conditioned reinforcing properties of a previously(More)
We hypothesize that drug addiction can be viewed as the endpoint of a series of transitions from initial voluntary drug use through the loss of control over this behaviour, such that it becomes habitual and ultimately compulsive. We describe evidence that the switch from controlled to compulsive drug seeking represents a transition at the neural level from(More)
Three groups of medicated and nonmedicated patients at different stages of Parkinson's disease and a group of neurosurgical patients with localized frontal lobe excisions were assessed on 2 novel tests of planning and spatial working memory. Results demonstrate that, like other tests of frontal lobe dysfunction, planning and spatial working memory are(More)
The idea that new memories undergo a time-dependent consolidation process after acquisition has received considerable experimental support. More controversial has been the demonstration that established memories, once recalled, become labile and sensitive to disruption, requiring "reconsolidation" to become permanent. By infusing antisense(More)
In this review we discuss the evidence that drug addiction, defined as a maladaptive compulsive habit, results from the progressive subversion by addictive drugs of striatum-dependent operant and Pavlovian learning mechanisms that are usually involved in the control over behaviour by stimuli associated with natural reinforcement. Although mainly organized(More)
Anatomically segregated systems linking the frontal cortex and the striatum are involved in various aspects of cognitive, affective, and motor processing. In this study, we examined the effects of combined unilateral lesions of the medial prefrontal cortex (mPFC) and the core subregion of the nucleus accumbens (AcbC) in opposite hemispheres (disconnection)(More)