Critical role for the mediodorsal thalamus in permitting rapid reward-guided updating in stochastic reward environments

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Abstract

Adaptive decision-making uses information gained when exploring alternative options to decide whether to update the current choice strategy. Magnocellular mediodorsal thalamus (MDmc) supports adaptive decision-making, but its causal contribution is not well understood. Monkeys with excitotoxic MDmc damage were tested on probabilistic three-choice decision-making tasks. They could learn and track the changing values in object-reward associations, but they were severely impaired at updating choices after reversals in reward contingencies or when there were multiple options associated with reward. These deficits were not caused by perseveration or insensitivity to negative feedback though. Instead, monkeys with MDmc lesions exhibited an inability to use reward to promote choice repetition after switching to an alternative option due to a diminished influence of recent past choices and the last outcome to guide future behavior. Together, these data suggest MDmc allows for the rapid discovery and persistence with rewarding options, particularly in uncertain or changing environments.

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Subhojit Chakraborty

Department of Bioengineering, Imperial College London, London, United Kingdom

Competing interests
The authors declare that no competing interests exist.
Nils Kolling

Department of Experimental Psychology, University of Oxford, Oxford, United Kingdom

Competing interests
The authors declare that no competing interests exist.
Mark E Walton

Department of Experimental Psychology, Oxford University, Oxford, United Kingdom

Competing interests
The authors declare that no competing interests exist.
Anna S Mitchell

Department of Experimental Psychology, Oxford University, Oxford, United Kingdom

For correspondence
anna.mitchell@psy.ox.ac.uk

Competing interests
The authors declare that no competing interests exist.

Ethics

Animal experimentation: All experimental procedures were performed in compliance with the United Kingdom Animals (Scientific Procedures) Act of 1986. A Home Office (UK) Project License (PPL 30/2678) obtained after review by the University of Oxford Animal Care and Ethical Review committee licensed all procedures. The monkeys were socially housed together in same sex groups of between two and six monkeys. The housing and husbandry were in compliance with the guidelines of the European Directive (2010/63/EU) for the care and use of laboratory animals. All neurosurgeries were performed under sevoflurane anaesthesia, with appropriate peri-operative medications as advised by our experienced veterinarian, and every effort was made to minimize pain, distress or lasting harm.

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.