The objective of this systematic review is to summarize the existing literature which examines the differences between addicted and healthy individuals in terms of the neural correlates of delayed reward discounting using MRI and fMRI.
Searches will be completed on MEDLINE/PubMed and PsycINFO.
No restrictions will be used in the search.
Additional search strategy information can be found in the attached PDF document (link provided below).
Types of study to be included
This review will include published peer-reviewed MRI or fMRI studies which have investigated the differences in brain structure or function between individuals with symptoms of addictive disorders and healthy individuals in the context of delayed reward discounting. Included studies will examine human subjects and will include a direct comparison between an addictive behavior group and a healthy group, or a continuous analysis of addictive behavior severity, with at least some subjects exhibiting significant addictive disorder symptoms. Studies must have involved participant completion of a delayed reward discounting task, which could have used monetary rewards or other types of rewards (e.g., drug rewards, primary reinforcers).
Condition or domain being studied
Addictive behaviors will be the clinical domain of focus in this review. Addictive behavior is defined based on the conditions included in the Diagnostic and Statistical Manual of Mental Disorder: fifth edition, and specifically will include addictive behavior in the context of tobacco, alcohol, other drugs, and gambling.
Participants must be either healthy individuals or individuals exhibiting addictive behavior in one of the above-stated categories.
The independent variables will focus on whether participants are exhibiting addictive behaviors, and the severity of these behaviors at the time the outcome variable has been collected. Participants will have been self-selected into these groups and not randomly assigned, thereby making the included studies quasi-experimental in design. The differences in outcome between addictive behavior positive and negative groups will be compared. Addictive behavior will be defined based on conditions included in the Diagnostic and Statistical Manual of Mental Disorder: fifth edition; and specifically will include addictive behavior in the context of tobacco, alcohol, other drugs, and gambling.
Individuals exhibiting addictive behaviors will be compared against healthy controls, and additionally, continuous effects among addicted individuals will also be assessed.
Included studies must have utilize MRI or fMRI methods.
Outcome measures for this review will be the assessment of brain function as it relates to delay discounting, measured by fMRI, and assessment of brain structure as it relates to delayed reward discounting measured by MRI.
Different units of measure will be obtained from these imaging modalities.
Regional brain activation and/or connectivity between brain regions will be the focus of studies utilizing fMRI and regional gray matter or white matter volume, surface area, or thickness will be the focus of studies utilizing MRI.
Data extraction, (selection and coding)
The two reviewers will independently record information from the studies included in the review in separate electronic spreadsheets. The following information will be extracted from each study: publication details (publication names, authors, year of publication, journal, and country), imaging modality, satisfaction of inclusion/exclusion criteria, data analysis strategy used, sample size, demographic characteristics of sample (age, ethnicity, sex), behavioral measures of delayed reward discounting task performance (e.g., k values, area under the curve), and any outcome measure pertaining to delayed reward discounting assessed in an included study (e.g., regional brain activation, regional gray matter volume, functional connectivity among regions).
Risk of bias (quality) assessment
Two independent reviewers will assess the overall quality of evidence using the criteria outlined in the GRADE framework, which makes reference to five domains: risk of bias, publication bias, consistency, directness, and precision. A rating for each domain and overall will be given for each outcome measure being investigated.
Strategy for data synthesis
A narrative review will be used to explicate the specific findings within the domains for each outcome measure, and we will evaluate evidence for and against the conclusion that there are differences between addicted and healthy populations. The strength of the evidence for this conclusion will be determined by the items assessed in the GRADE framework described above. Areas needing further study will be highlighted and suggestions for future study will be made.
Analysis of subgroups or subsets
Contact details for further information
Max M Owens
265 Boulevard Hts., Unit B
Organisational affiliation of the review
University of Georgia
Mr Max M. Owens, University of Georgia Dr Michael Amlung, Peter Boris Centre for Addiction Research, St. Joseph’s Healthcare Hamilton/McMaster University Dr Steven Beach, University of Georgia Dr Lawrence Sweet, University of Georgia Dr James MacKillop, Peter Boris Centre for Addiction Research, St. Joseph’s Healthcare Hamilton/McMaster University
Anticipated or actual start date
17 March 2017
Anticipated completion date
30 September 2017
Support for this study was provided by the Center for Translational and Prevention Science (P30 DA027827, Brody-PI) funded by the National Institute on Drug Abuse.
Formal screening of search results against eligibility criteria
Risk of bias (quality) assessment
PROSPERO This information has been provided by the named contact for this review. CRD has accepted this information in good faith and registered the review in PROSPERO. CRD bears no responsibility or liability for the content of this registration record, any associated files or external websites.