Disturbances Across Whole Brain Networks During Reward Anticipation in an Abstinent Addiction Population
Abstract
Introduction
The prevalent spatial distribution of abnormalities reported in cognitive fMRI studies in addiction suggests there are extensive disruptions across whole brain networks. Studies using resting state have reported disruptions in network connectivity in addiction, but these studies have not revealed characteristics of network functioning during critical psychological processes that are disrupted in addiction populations. Analytic methods that can capture key features of whole brain networks during psychological processes may be more sensitive in revealing additional and widespread neural disturbances in addiction, that are the provisions for relapse risk, and targets for medication development.
Method
The current study compared a substance addiction (ADD; n = 83) group in extended abstinence with a control (CON; n = 68) group on functional MRI (voxel-wise activation) and global network (connectivity) measures related to reward anticipation on a monetary incentive delay task.
Results
In the absence of group differences on MID performance, the ADD group showed reduced activation predominantly across temporal and visual regions, but not across the striatum. The ADD group also showed disruptions in global network connectivity (lower clustering coefficient and higher characteristic path length), and significantly less connectivity across a sub-network comprising frontal, temporal, limbic and striatal nodes.
Conclusions
These results show that an addiction group in extended abstinence exhibit localized disruptions in brain activation, but more extensive disturbances in functional connectivity across whole brain networks. The researchers propose that measures of global network functioning may be more sensitive in highlighting latent and more widespread neural disruptions during critical psychological processes in addiction and other psychiatric disorders.
Research ian context
In this study, the researchers examined the brains of 68 control individuals and 83 currently abstinent individuals. Substances used in the second group included alcohol, cocaine, and opiates. They used a monetary incentive delay task to measure brain activity while waiting for a reward, a psychological process with demonstrated abnormalities among addicted and recovering individuals.
The two groups were well-matched in terms of their performance in the task. However, the addiction-group showed significant disruptions at a global level, with reduced clustering and higher path length.
In network analysis, clustering coefficient is a key measure of connectivity, increasing with the average number of connections between nodes (in this case, brain sites). Path length refers to the minimum distance in a network that information has to travel to get from one point to another; the more connected a network, the lower the path length.
- In the study, the addiction-group showed low clustering coefficients and high paths lengths. This means there was an overall reduced state of inter-region connectivity.
- Network analysis, demonstrated disruptions in reward-related connectivity in the addiction-group, touching on cognitive, striatal and limbic regions.
