Deficits in context-dependent adaptive coding of reward in schizophrenia.

Matthias Kirschner,Stefan Kaiser,Martin Bischof,Philippe N Tobler,Erich Seifritz,Matthias N Hartmann-Riemer,Oliver M Hager,Agne Kluge

doi:10.1038/npjschz.2016.20

Abstract

Theoretical principles of information processing and empirical findings suggest that to efficiently represent all possible rewards in the natural environment, reward-sensitive neurons have to adapt their coding range dynamically to the current reward context. Adaptation ensures that the reward system is most sensitive for the most likely rewards, enabling the system to efficiently represent a potentially infinite range of reward information. A deficit in neural adaptation would prevent precise representation of rewards and could have detrimental effects for an organism’s ability to optimally engage with its environment. In schizophrenia, reward processing is known to be impaired and has been linked to different symptom dimensions. However, despite the fundamental significance of coding reward adaptively, no study has elucidated whether adaptive reward processing is impaired in schizophrenia. We therefore studied patients with schizophrenia (n=27) and healthy controls (n=25), using functional magnetic resonance imaging in combination with a variant of the monetary incentive delay task. Compared with healthy controls, patients with schizophrenia showed less efficient neural adaptation to the current reward context, which leads to imprecise neural representation of reward. Importantly, the deficit correlated with total symptom severity. Our results suggest that some of the deficits in reward processing in schizophrenia might be due to inefficient neural adaptation to the current reward context. Furthermore, because adaptive coding is a ubiquitous feature of the brain, we believe that our findings provide an avenue in defining a general impairment in neural information processing underlying this debilitating disorder.

Highlights

Response times were faster in the high-reward context, indicating that participants adapted their behavior to the different reward context
The present findings suggest that patients with SZ have deficits in adaptive coding of rewards due to a diminished discriminability of different reward amounts, which leads to an imprecise representation of reward information
We show that the adaptive coding deficit is related to total symptom severity, suggesting that this deficit could reflect npj Schizophrenia (2016) 16020

Summary

Introduction

Reward information is represented across several cortical and subcortical brain regions related to the dopaminergic system, such as the striatum, the orbitofrontal cortex, and the medial temporal cortices.[1,2,3] Emerging evidence suggests that these representations are context specific, such that they adjust to the rewards that are available and likely in the current context.[4,5,6,7] The dynamic adjustment in the firing of reward-sensitive dopaminergic neurons to the current context is known as adaptive coding of reward.[8,9] This adaptation is necessary, because the coding range of any neuron, including reward-sensitive neurons, is limited (i.e., the firing rate can increase only up to some degree and can resolve small input differences only with limited precision), whereas the diversity and range of potential inputs, including rewards, in our daily life is theoretically unlimited. In principle the issue could be mitigated somewhat by increasing the number of recruited neurons with increasing reward amounts, the problem remains that for each neuron small amount differences can be resolved only with limited precision

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Conclusion