Decoding reward signals in the brain: Functional neural correlates of individual reward valuation and reward learning

Abstract

This dissertation consists of two projects investigating the functional neural representations of value in sexual stimuli and the commonalities between appetitive and aversive conditioning. In the first project, the focus was on understanding the individual value representation of visual sexual stimuli (VSS) based on individual ratings. Using functional magnetic resonance imaging (fMRI), 72 men viewed VSS film clips, and their ratings of sexual arousal and valence were collected. The results revealed positive correlations between neural activation in regions associated with reward valuation (nucleus accumbens, caudate nucleus, and orbitofrontal cortex) and individual ratings of VSS. Additionally, the strength of the association between neural activation and sexual arousal ratings was positively correlated with self-reported symptoms of problematic pornography use, indicating altered VSS valuation processes in individuals with extensive exposure to VSS. The second project aimed to explore the functional neural commonalities between appetitive and aversive conditioning. While aversive conditioning has been extensively studied, with well-established neural networks, the neural correlates of appetitive conditioning have garnered increasing attention. This project sought to compare the neural response patterns between aversive and appetitive paradigms. Three independent datasets were utilized, each consisting of participants who performed a differential conditioning task in an fMRI scanner. The task involved rewarding an appetitive conditioned stimulus (CS+) with money, while another stimulus (CS-) was unrewarded. The analysis focused on testing pattern expression and similarity between aversive and appetitive conditioning data across the datasets. The results demonstrate significant similarities in neural response patterns related to aversive and appetitive conditioning across different samples, utilizing cosine similarity and classification accuracy measures. Overall, this dissertation contributes to understanding the neural mechanisms underlying the individual value representation of sexual stimuli and the commonalities between appetitive and aversive conditioning. The findings shed light on the processes involved in reward valuation and highlight the potential similarities between different types of conditioning paradigms, which may have implications for our understanding of valence-independent motivational systems and learning processes.