The successor representation in high-risk drinking and alcohol-related contexts

The successor representation (SR) is a reinforcement learning strategy which has been suggested to underlie nuanced forms of habitual behavior, rendering it a candidate mechanism for mental health conditions thought to involve habitual control, such as addiction. However, paradigms used to assess habits in humans cannot detect SR use. Together with the fact that they are usually conducted in disorder-irrelevant contexts, this may explain why the evidence for a hypothesized shift from goal-directed to habitual behavior in addiction is inconsistent. Here, we tested whether individuals with high-risk (n = 260) compared to low-risk drinking behavior (n = 260) rely more on SR or a rigid goal-based dimension-reduced SR variant, particularly in alcohol-related contexts. An online multi-stage decision-making task performed in either a virtual bar or apartment context allowed us to dissociate (red)SR from model-based and model-free learning strategies by testing how well participants adapted their choices to different types of distal changes in the environment. Findings suggest that a particular type of SR, namely a (reduced) random-policy SR-like strategy, contributes to human behavior, but that high-risk drinkers do not differ from low-risk drinkers in their use of this strategy. Instead, both groups seem to rely less on what is likely a (reduced) random-policy SR strategy in alcohol-related contexts – and instead more on model-free control. Results suggest that the use of an adaptive, resource-efficient decision-making strategy is selectively downregulated in substance-related contexts. This study highlights the importance of considering contextual modulation and nuanced decision strategies in understanding habitual and goal-directed behavior in mental health conditions such as addiction.Author summary: Humans can behave in more habitual or more goal-directed ways, like when routinely brushing our teeth versus planning how to circumvent a construction site. Mental health conditions such as addiction have been suggested to involve a shift from goal-directed to habitual behavior, but the evidence is inconsistent. This might be due to how habits have been assessed in the laboratory: tasks usually take place in contexts unrelated to the disorder and cannot detect the use of strategies with subtle characteristics of habitual behavior. Here, we set out to determine the role of one such strategy, the successor representation, in high-risk drinking and alcohol-related contexts. While we found no increased use of this strategy in high-risk drinking, individuals likely relied less on a successor representation-based strategy in a virtual bar environment compared to a non-alcohol-related context. Drug-associated settings thus seem to be associated with diminished reliance on a generally adaptive, efficient behavioral strategy. Our findings highlight that, to understand the role of habits in mental health conditions, we need to consider decision-making strategies along a continuum between goal-directed and habitual control and, importantly, disorder-relevant contexts.