Acquisition of Conditioning between Methamphetamine and Cues in Healthy Humans

Methamphetamine, amphetamine, and aggression in humans: A systematic review of drug administration studies

The relationship between amphetamine use and aggressive or violent behaviour is unclear. This review examined laboratory data collected in humans, who were administered an acute dose of amphetamine or methamphetamine, in order to investigate the link between amphetamines and aggression. It is registered with PROSPERO (CRD42019127711). Included in the analysis are data from twenty-eight studies. Behavioural and/or subjective measures of aggression were assessed in one thousand and sixty-nine research participants, with limited amphetamine-use histories, following a single amphetamine dose (0-35mg). The available published evidence indicates that neither amphetamine nor methamphetamine acutely increased aggression as assessed by traditional laboratory measures. Future research should assess supratherapeutic amphetamine doses as well as include a broader range of multiple aggression measures, facilitating simultaneous assessment of the various components that comprise this complex, multifaceted construct.

Acute methylphenidate administration reduces cocaine-cue attentional bias

Mechanistic research on behavioral processes underlying substance use disorder might help identify novel targets for interventions development. Drug-related attentional bias and response inhibition deficits have received a great deal of consideration in substance use research, broadly, and cocaine use research, specifically. Studies investigating pharmacological mechanisms that may ameliorate, or further impair, these behaviors relevant to cocaine use are relatively lacking. This study evaluated the impact of acute administration of methylphenidate, a dopamine-favoring reuptake inhibitor, on both gaze-related cocaine-cue-attentional bias and cocaine-cue related disruptions in response inhibition among individuals with cocaine use disorder. Participants (N = 12; 33% female) completed a within-subject, outpatient, acute dosing study. Two sessions were completed in which methylphenidate (60 mg) or placebo were administered followed by completion of an attentional bias task using eye-tracking technology and neutral-cue and cocaine-cue response inhibition tasks. Subjective and physiological effects were also recorded. Significant cocaine cue attentional bias and response inhibition failures were observed during placebo administration. Acute methylphenidate administration reduced cocaine-cue attentional bias as measured by cocaine-cue gaze fixations (d_z = 1.04; Bayes Factor = 12.37). No statistically significant effects of methylphenidate were observed on response inhibition (Bayes Factors = 0.17-1.04). Methylphenidate produced prototypical subjective and physiological effects. Although the small sample should be considered, these findings indicate acute manipulation of dopaminergic activity reduced cue-related attentional allocation related to cocaine use disorder. Future research evaluating alternative dopaminergic agents and applications within a clinical setting are needed to determine the clinical significance of targeting this neurobehavioral mechanism.

A Scoping Review on Cue Reactivity in Methamphetamine Use Disorder

The experience of craving via exposure to drug-related cues often leads to relapse in drug users. This study consolidated existing empirical evidences of cue reactivity to methamphetamine to provide an overview of current literature and to inform the directions for future research. The best practice methodological framework for conducting scoping review by Arkey and O'Malley was adopted. Studies that have used a cue paradigm or reported on cue reactivity in persons with a history of methamphetamine use were included. Databases such as Medline, EMBASE, PsycINFO and CINAHL were searched using key terms, in addition to citation check and hand search. The search resulted in a total of 32 original research articles published between 2006 to 2020. Three main themes with regard to cue reactivity were identified and synthesized: (1) effects of cue exposure, (2) individual factors associated with cue reactivity, and (3) strategies that modulate craving or reactivity to cues. Exposure to methamphetamine-associated cues elicits significant craving and other autonomic reactivity. Evidence suggests that drug cue reactivity is strongly associated with indices of drug use and other individual-specific factors. Future studies should focus on high quality studies to support evidence-based interventions for reducing cue reactivity and to examine cue reactivity as an outcome measure.

Neural responses to cues paired with methamphetamine in healthy volunteers

Drug cues, or conditioned responses to stimuli paired with drugs, are widely believed to promote drug use. The acquisition of these conditioned responses has been well characterized in laboratory animals: neutral stimuli paired with drugs elicit conditioned responses resembling the motivational and incentive properties of the drug itself. However, few studies have examined acquisition of conditioning, or the nature of the conditioned response, in humans. In this study, we used fMRI to examine neural responses to stimuli that had been paired with methamphetamine or placebo in healthy young adults. Participants first underwent four conditioning sessions in which visual-auditory stimuli were paired with either methamphetamine (20 mg, oral) or placebo. Then on a drug-free test day, the stimuli were presented during an fMRI scan to assess neural responses to the stimuli. We hypothesized that the stimuli would elicit drug-like brain activity, especially in regions related to reward. Instead, we found that the methamphetamine-paired stimuli, compared to placebo-paired stimuli, produced greater activation in regions related to visual and auditory processing, consistent with the drug's unconditioned effects on sensory processing. This is the first study to demonstrate conditioned neural responses to drug-paired stimuli after just two pairings of methamphetamine in healthy adults. The study also illustrates that conditioned responses may develop to unexpected components of the drug's effects.