1,721,065 research outputs found
Attentional bias modification in substitute-prescribed opiate users and control participants
Get PDFThis thesis investigated biases in the implicit processing of substance-related cues in substance users. Part 1, a literature review, assessed the effectiveness of attempts to modify such processes and the wider benefits of doing so. The 12 studies reviewed, addressing between them attentional bias, implicit attitudes and approach bias in either alcohol drinkers or tobacco smokers, suggest that implicit processes are readily modifiable. However, the evidence of wider benefit is less clear. The clinical implications and future research considerations are discussed. Part 2 is an empirical paper, conducted jointly with a fellow trainee clinical psychologist, which assessed the effects of attentional bias modification (ABM) in opiate dependent and non-substance using control participants. Baseline differences in attentional bias (AB) between these groups were assessed, as were the effects of ABM on AB and craving. The role of treatment adherence (i.e. whether or not an individual was using illicit opiates on top of their prescribed substitute) was also explored. Contrary to predictions, there were no baseline group differences in AB, and ABM had no significant effects on AB or craving. However, treatment adherence was an important factor, with differences found between opiate dependent participants using on top, not using on top and control participants on measures of AB, craving and psychopathology. The clinical and research implications of these differences are discussed. Finally, Part 3, the critical appraisal, provides reflections on the entire research process. Some guidance and recommendations are also offered to future researchers covering areas such as the difficulties in recruiting from these clinical populations, and possible alternative approaches to the problem of biases in implicit processes in substance use
Interactions between Cannabinoids and Tobacco: Implications for understanding and treating addictive disorders
Get PDFCannabis and tobacco are two of the most commonly used drugs in the world and their use often co-occurs. Cigarette smoking continues to be a global epidemic where novel drugs for smoking cessation are necessary. In chapter 1, I review the literature concerning cannabis, tobacco and co-used cannabis and tobacco, in relation to their prevalence and effects on cognition, addiction and psychosis. In chapter 2, I provide a ‘worldwide’ overview of routes of administration (ROA) of cannabis with and without tobacco (n=33, 687). Tobacco-based ROAs were most common in Europe (77.2–90.9%) and Australasia (20.7–51.6%) but uncommon in the Americas (4.4–16.0%). Tobacco-based ROAs were associated with reduced motivation to quit tobacco. In chapter 3, I describe the first investigation of the individual and interactive effects of cannabis and tobacco in a randomized, placebo-controlled, double-blind crossover design (n=24). I found tobacco may offset effects of cannabis on delayed recall, had no effect of cannabis-induced psychotomimetic or subjective effects and was more harmful for cardiovascular outcomes. In chapter 4, in the same sample, I found tobacco did not influence the rewarding effects of cannabis. In chapter 5, in the same sample, I developed an innovative “roll a joint” paradigm to assess quantity of both drugs. I found self-reported quantity was accurate for tobacco but overestimates cannabis exposure. In chapter 6 and 7, in a sample of overnight-abstinent dependent cigarette smokers (n=30), I investigated if cannabidiol (CBD) can reduce nicotine withdrawal. Results showed CBD reduced attentional bias and pleasantness ratings but increased errors on the go/no-go, compared to placebo. There were no effects on verbal episodic, working memory or delay discounting. Finally, in chapter 8, I summarise and integrate my findings into the literature, discuss implications, consider limitations and suggest future research on the interaction between cannabinoids and tobacco
Psychotic-like symptomatology and reward responsivity in chronic ketamine and cannabis users
Get PDFThis thesis assesses psychotic-like symptomatology and reward responsivity in chronic users of two illicit drugs, cannabis and ketamine. As use of these drugs is steadily increasing, with cannabis being the most widely used drug worldwide (following alcohol, caffeine and tobacco) and the recent proliferation of ketamine misuse in parts of Asia, Europe and the United States, it is important to examine the effects of their habitual use. While research has linked cannabis use to sub-clinical psychotic-like symptoms, longitudinal studies examining the association between cannabis use, psychotic-like symptoms and transition to psychosis have revealed mixed findings. Additionally, although acute ketamine administration has been shown to produce psychotic-like symptoms in drug-naïve volunteers, there has been less research on the effects of chronic ketamine use. Part 1 of the thesis is a literature review investigating the assessment of cannabis use in studies of individuals meeting clinical ‘high risk’ criteria for transition to psychosis. It examines measures of cannabis use, as well as findings regarding the association between cannabis and subsequent conversion to psychosis. It also examines whether such studies measured further significant outcome variables, such as social and role functioning. Finally, the literature review considers the limitations in how cannabis use has been assessed and the implications of this for future research on the extent to which cannabis influences the development of psychotic-like symptomatology and risk of conversion to frank psychosis. Part 2 of the thesis comprises an investigation of symptoms of prodromal psychosis and reward responsiveness in three groups – chronic users of cannabis, ketamine, and healthy controls. This investigation formed part of a joint project conducted with one other trainee clinical psychologist examining the chronic effects of cannabis and ketamine use on psychosis proneness and cognitive functioning. The empirical paper reports a between subjects study, comparing 20 cannabis users, 20 ketamine users and 20 healthy controls on a number of self-report measures indexing depression (BDI-II), psychosis-like symptoms and schizotypy (PQ-B and O-LIFE), and trait anhedonia (TEPS), and on two laboratory-based tasks assessing reward sensitivity (the ‘Probabilistic Reward Task’) and effort-based decision making (the ‘Effort-Expenditure for Rewards Task’). Both drug using groups were found to have higher levels of schizotypy (O-LIFE) and positive psychosis symptomatology (PQ-B) than controls, while group differences were found on the probabilistic reward task, with controls demonstrating greater response bias than cannabis users and greater discriminability than ketamine users. No group differences were found on the effort-based decision-making task. A critical appraisal of the research forms Part 3 of the thesis. It describes the process of working collaboratively on the project rationale and design, reflections on recruiting and working with drug using participants, and thoughts on clinical implications of the project
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Episodic Simulation of Future Events in Dependent and Non-dependent Daily Cannabis Users
Get PDFOVERVIEW: This thesis investigates the Episodic Simulation of Future Events (ESoFE) within two populations; cannabis users and individuals diagnosed with psychosis. Part one provides a narrative synthesis of literature investigating the hypothesis that individuals with psychosis show an impairment in ESoFE. Psychosis spectrum studies investigating ESoFE in analogue samples with psychotic traits were also included. Evidence was found for individuals with psychosis to demonstrate an impairment on some measures of ESoFE, but only under certain task conditions. Preliminary evidence for an ESoFE enhancement in analogue samples with psychotic traits was also identified. In light of the methodological inconsistencies across studies, recommendations are made for the development of a standardised ESoFE measure, as well as for the literature to be organised around an agreed taxonomy of future-orientated cognition. Part two is an empirical paper examining how cannabis use affects ESoFE in both dependent and non-dependent daily cannabis users. Both cannabis-using groups were compared with non-cannabis-using controls on an ESoFE task which required participants to imagine future events related to cue sentences. ESoFE differences were observed between the two cannabis-using groups, but not between either cannabis-using group and controls. Non-dependent users provided richer descriptions of their cannabis related future events than dependent users, and this was taken as evidence for a cannabis ESoFE ‘bias’ in non-dependent users relative to dependent users. The findings have potential implications for treatment programmes requiring cannabis-dependent individuals to project themselves into the future. Part three provides an appraisal of the research process, including an account of why the research area was chosen, critical reflections on the methodology, and some concluding reflections on how the author’s experiences of research and clinical practice have enriched one another. This was a joint project with fellow DClinPsy student, Ruth Braidwood (Braidwood, 2017). Jon Waldron (MSc student) was also involved in recruitment and data collection. See Appendix 1 for a breakdown of contributions
Salience attribution in addiction and psychosis
Get PDFSalience attribution, the process by which particular stimuli come to selectively grab one’s attention, is heightened towards drug-associated cues in substance users and irrelevant cues in psychosis. In Chapter 1 I review this literature. Despite their theoretical link and the substantial co-morbidity of substance use in psychotic disorders, the extent to which these processes overlap is not well understood. The aim of this thesis was to investigate their relationship. The ability of drug cues to impact on associative learning processes was examined in Chapter 2 using a newly developed task. Overshadowing by drug cues was found alongside smoking-related attentional bias in abstinent smokers but not in satiated smokers or controls. This overshadowing effect is replicated in Chapter 3 among frequent ketamine users and polydrug-using controls. Ketamine users showed elevated psychotic-like symptoms, a reduction in associative blocking and a stronger impact of drug cues on blocking compared to polydrug controls. These results are indicative of a shared disruption of salience attribution in addiction and psychosis, which I investigated in Chapter 4 among smokers with a diagnosis of schizophrenia. Associative blocking was reduced in these individuals compared to control smokers but both groups displayed an absence of blocking towards drug cues. The patient group also showed higher drug-cue attentional bias that correlated with positive psychotic symptoms. In Chapter 5 I examined the role of dopamine in salience attribution in smokers. The dopamine D2/D3 agonist pramipexole (0.5mg) reduced urges to smoke and decreased attentional bias towards smoking-related images relative to monetary images when compared to placebo. In Chapter 6 I discuss the theoretical and clinical implications of these findings. The effects of drug cues on associative learning provide a methodological advance, and these findings offer preliminary support for a link between disruptions of salience attribution in addiction and in psychosis
Manipulating Maladaptive Motivational Memories via Reconsolidation
Get PDFSubstance Use Disorders (SUDs), are generally viewed as disorders of maladaptive reward memory and motivation. In SUDs, memories formed during drug use associate environmental stimuli with the rewarding effects of drugs. These stimuli can subsequently trigger craving, highly motivated drug-seeking and relapse, even after years of abstinence. An exciting new approach to combatting these maladaptive memories is via reconsolidation, the process by which memories become briefly unstable upon recall in order to strengthen or update before restabilising. In Chapter 1, I review reward memory mechanisms in SUDs along with pharmacological and behavioural determinants of memory reconsolidation to identify potential drug targets for interfering with reconsolidation. In Chapter 2, I use meta-analysis to assess the effects of two classes of drugs; N-methyl D-aspartate (NMDAR) antagonists and β-Blockers on blocking reconsolidation of reward memory in rats and show that NMDAR antagonism is far more effective. Building on this knowledge, in Chapter 3, I show that 10mg of the NMDAR antagonist memantine in combination with the retrieval of smoking cue-drug memory does not affect relapse or craving in a group of quitting smokers. As this null finding may have represented either a failure to destabilise memories or inefficacy of memantine, in Chapter 4 I use a reward conditioning paradigm in hazardous drinkers to show that NMDAR antagonist Nitrous Oxide can interfere with reconsolidation of cue-alcohol memory, when administered after a reminder of learning that induces a negative prediction error. Chapter 5 builds on emerging evidence of the necessity of prediction error to destabilise memory, using guided expectancy violation to destabilise naturalistic cue-alcohol memories in hazardous drinkers. Subsequent disgust counterconditioning updated these memories, reducing motivational salience and liking of alcohol stimuli, with associated reduction in drinking. In Chapter 6 I discuss the research reported and suggest directions for further study
Drug and non-drug reward processing in cigarette and cannabis users
Get PDFMost people who try psychoactive drugs never become addicted. Theoretically, hypersensitivity to drug rewards and hyposensitivity to non-drug rewards may contribute to the development of drug addiction. In chapter 1, I review this literature, focusing on the psychology and neuroscience of reward processing, in nicotine and cannabis addictions. In chapter 2, using a novel task (the DReaM-Choice), I demonstrate that dependent (n=20), compared with occasional smokers (n=20), had greater motivation for and liking of cigarettes, but displayed little evidence of a difference in non-drug reward processing. Surprisingly, I also show the effects of 12 hour abstinence on reward processing were similar in dependent and occasional smokers. I then report a functional magnetic-resonance-imaging (fMRI) experiment (chapter 3), in which dependent smokers (n=22) had greater behavioural motivation for cigarettes and a stronger neural response to winning cigarettes than occasional smokers (n=20). However, there were no differences between the groups in behavioural or neural processing of the non-drug reward (music). I attempted to lessen the motivation to smoke cigarettes in the study reported in chapter 4, by administering a dopamine D2/3 receptor agonist (0.5mg pramipexole) to both dependent (n=20) and occasional (n=20) smokers. Pramipexole had no impact on motivation to smoke cigarettes, though it did impair reward learning and effort-related decision-making for monetary reward. In chapter 5, I found that, in non-dependent cannabis users (n=17), acutely administered cannabis reduced motivation for monetary reward; an effect which was moderated by the presence of cannabidiol in the cannabis. In a separate study, I demonstrate that dependent cannabis users (n=20) had impaired reward learning, but were not amotivated, relative to non-dependent, drug-using controls (n=20). Finally, in chapter 6, I summarise my findings, discuss their theoretical and clinical implications, consider their limitations and suggest future research directions for the field of reward processing in addiction
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