Imaging brain response to reward in addictive disorders

Area of Science:

• Neuroscience
• Psychiatry
• Addiction Research

Background:

• Addiction is a complex disorder involving alterations in the brain's reward system.
• Two major hypotheses attempt to explain these alterations: the impulsivity hypothesis and the reward-deficiency hypothesis.

Purpose of the Study:

• To compare neuroimaging evidence supporting or refuting the impulsivity and reward-deficiency hypotheses of addiction.
• To reconcile discrepancies in findings between different neuroimaging techniques.

Main Methods:

• Review and comparison of human neuroimaging studies, including Positron Emission Tomography (PET) and functional Magnetic Resonance Imaging (fMRI).
• Analysis of studies examining dopamine receptor density, dopamine release, and goal-directed behavior in the context of addiction.

Main Results:

• PET studies provide strong support for the reward-deficiency hypothesis, indicating reduced responses to non-drug rewards.
• fMRI studies offer conflicting evidence, supporting aspects of both the impulsivity and reward-deficiency hypotheses.
• Differences in measurement timescales between PET and fMRI may explain some result discrepancies.

Conclusions:

• Both the impulsivity and reward-deficiency hypotheses likely contribute to the complex pathophysiology of addiction.
• A comprehensive understanding of addiction requires integrating findings related to both reward processing and inhibitory control deficits.