Resting state functional connectivity in addiction: drug abuse and reward dysregulation
MetadataShow full item record
INTRODUCTION: With the advent of advanced neuroimaging, strides have been made towards better understanding the cognitive elements necessary for task processing. Resting state functional connectivity assessments using functional magnetic resonance imaging has allowed patient assessments of underlying neural networks in patient populations with variable constraints. Drug addiction, a chronically relapsing disorder, presents many variable constraints. Cellular and molecular changes in neural reward pathway of drug addicted patient populations have advanced, but circuit-level alterations with reward deficits are yet to be completely understood. Resting state functional connectivity investigations in patient populations that use illicit drugs are seen to have repercussions on neural networks. OBJECTIVE: Assess and compare reward-network resting state functional connectivity investigations in patient populations with illicit drug use. METHODS: A meta-analysis of several resting state functional connectivity studies. Patient populations for each study contained an experimental group of drug users with a group of non-drug using controls to assess changes in resting state functional connectivity of the reward network. Studies utilized Diagnostic and Statistical Manuel of Mental disorders, 4th edition, as the basis of diagnosing drug dependence and abuse. A 3 Tesla MRI scanner was utilized to assess the reward pathway of the drug abuse in all experiments with the exception of one group using a 4 Tesla scanner. Band-pass temporal filtering from roughly 0.01 Hz to 0.1 Hz on residual signals was used to obtain low-frequency fluctuations needed for resting state connectivity analyses. Correlation maps were created by computing the correlation coefficients between the blood oxygen level dependent time course from the seed regions and from all other brain voxels. Regions of interest were chosen based on data from databases or previous studies. RESULTS: Four papers found widespread reductions in the connectivity of multiple reward pathway components. Results of these studies are consistent with perspectives suggesting that transition from drug use to addiction is driven by reduced functioning of reward systems and concurrently increased activation of anti-reward systems. Two studies suggested an increase in reward pathway of drug use, suggesting enhanced connectivity within reward and motivation circuits may be interpreted in the perspective of altered incentive salience for drugs and drug-associated stimuli. CONCLUSION: At early stage of experimental data in this field, data interpretation necessitates caution. Small sample sizes, heterogeneous subject groups and variable experimental paradigms may have lead to opposing findings. With certainty, chronic drug use was found to alter reward pathway in patient populations.