Reward processing in schizophrenia: a deficit in the representation of value

Abstract

Patients with schizophrenia demonstrate deficits in motivation and learning that suggest impairment in different aspects of the reward system. In this article, we present the results of 8 converging experiments that address subjective reward experience, the impact of rewards on decision making, and the role of rewards in guiding both rapid and long-term learning. All experiments compared the performance of stably treated outpatients with schizophrenia and demographically matched healthy volunteers. Results to date suggest (1) that patients have surprisingly normal experiences of positive emotion when presented with evocative stimuli, (2) that patients show reduced correlation, compared with controls, between their own subjective valuation of stimuli and action selection, (3) that decision making in patients appears to be compromised by deficits in the ability to fully represent the value of different choices and response options, and (4) that rapid learning on the basis of trial-to-trial feedback is severely impaired whereas more gradual learning may be surprisingly preserved in many paradigms. The overall pattern of findings suggests compromises in the orbital and dorsal prefrontal structures that play a critical role in the ability to represent the value of outcomes and plans. In contrast, patients often (but not always) approach normal performance levels on the slow learning achieved by the integration of reinforcement signals over many trials, thought to be mediated by the basal ganglia.

Fig. 1.

Average Pleasantness Ratings of Affectively Valenced International Affective Picture System (IAPS) Stimuli. There were no group differences for any slide valence category (P = .14). Participants’ ratings did not differ from the average IAPS rating (gray-shaded regions; P‘s > .26).

Fig. 2.

Speeded Button Pressing for Negative, Neutral, and Positive IAPS Stimuli. In the representational responding condition, participants pressed to indicate whether they did or did not wish to see each slide again later. In this condition, stimuli were not visible during responding. In the evoked responding condition, participants pressed to increase or decrease viewing time while slides were on the screen. We also show the average correlation between each participant's rating and button-pressing behavior across conditions. Participants with schizophrenia had more difficulty calibrating their responses to stimulus valence than did healthy participants (P = .001), particularly in the representational responding condition (P = .02).

Fig. 3.

Decreases in Subjective Reward Value Over Time in Healthy Participants and Participants With Schizophrenia. Participants with schizophrenia showed greater discounting of future rewards than did healthy participants (P = .03).

Fig. 4.

(a) (Top panel) Accuracy on Cards 1–4 by Subject Group.(b) (Bottom panel) Early accuracy predicts overall task success. Of the patients with the poorest accuracy on Cards 2–4, 69% were unable to complete more than 2 categories. Of the patients with good accuracy on Cards 2–4, 62% completed 5 or more categories.

Fig. 5.

Performance of schizophrenia (SZ) Patients and Controls on 2 Measures from the Reversal Learning Paradigm Used by Waltz and Gold. Although patients and controls achieved similar numbers of initial discriminations (t(58) = 0.69), patients achieved far fewer reversal than controls on the task (t(58) = 2.70; P = .01).

Fig. 6.

Performance of schizophrenia (SZ) Patients and Controls on Transfer Measures from the Frank Probabilistic Selection Paradigm (Waltz et al61). Patients showed significant impairment, relative to controls, on the measure of procedural Go learning (choosing the best stimulus at test, in all pairings; t(54) = 2.85; P = .01). By contrast, patients and controls performed similarly on the measure of procedural NoGo learning (avoiding the worst stimulus at test, in all pairings; t(54) = 0.40).