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Biol Psychiatry. 2019 Jun 1;85(11):936-945. doi: 10.1016/j.biopsych.2018.12.017. Epub 2019 Jan 4.

Model-Free and Model-Based Influences in Addiction-Related Behaviors.

Author information

1
Department of Psychiatry, Yale University, New Haven, Connecticut. Electronic address: stephanie.groman@yale.edu.
2
Department of Neuroscience, Yale University, New Haven, Connecticut.
3
Department of Psychiatry, Yale University, New Haven, Connecticut.
4
Department of Psychiatry, Yale University, New Haven, Connecticut; Department of Neuroscience, Yale University, New Haven, Connecticut; Department of Psychology, Yale University, New Haven, Connecticut.
5
Department of Psychiatry, Yale University, New Haven, Connecticut; Department of Psychology, Yale University, New Haven, Connecticut. Electronic address: jane.taylor@yale.edu.

Abstract

BACKGROUND:

Disruptions in the decision-making processes that guide action selection are a core feature of many psychiatric disorders, including addiction. Decision making is influenced by the goal-directed and habitual systems that can be computationally characterized using model-based and model-free reinforcement learning algorithms, respectively. Recent evidence suggests an imbalance in the influence of these reinforcement learning systems on behavior in individuals with substance dependence, but it is unknown whether these disruptions are a manifestation of chronic drug use and/or are a preexisting risk factor for addiction.

METHODS:

We trained adult male rats on a multistage decision-making task to quantify model-free and model-based processes before and after self-administration of methamphetamine or saline.

RESULTS:

Individual differences in model-free, but not model-based, learning prior to any drug use predicted subsequent methamphetamine self-administration; rats with lower model-free behavior took more methamphetamine than rats with higher model-free behavior. This relationship was selective to model-free updating following a rewarded, but not unrewarded, choice. Both model-free and model-based learning were reduced in rats following methamphetamine self-administration, which was due to a decrement in the ability of rats to use unrewarded outcomes appropriately. Moreover, the magnitude of drug-induced disruptions in model-free learning was not correlated with disruptions in model-based behavior, indicating that drug self-administration independently altered both reinforcement learning strategies.

CONCLUSIONS:

These findings provide direct evidence that model-free and model-based learning mechanisms are involved in select aspects of addiction vulnerability and pathology, and they provide a unique behavioral platform for conducting systems-level analyses of decision making in preclinical models of mental illness.

KEYWORDS:

Computational psychiatry; Dopamine; Drug addiction; Methamphetamine; Model-based reinforcement learning; Model-free reinforcement learning

PMID:
30737015
PMCID:
PMC6534429
[Available on 2020-06-01]
DOI:
10.1016/j.biopsych.2018.12.017

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