The neural underpinnings of associative learning in health and psychosis: how can performance be preserved when brain responses are abnormal?

Abstract

Associative learning experiments in schizophrenia and other psychoses reveal subtle abnormalities in patients' brain responses. These are sometimes accompanied by intact task performance. An important question arises: How can learning occur if the brain system is not functioning normally? Here, we examine a series of possible explanations for this apparent discrepancy: (1) standard brain activation patterns may be present in psychosis but partially obscured by greater noise, (2) brain signals may be more sensitive to real group differences than behavioral measures, and (3) patients may achieve comparable levels of performance to control subjects by employing alternative or compensatory neural strategies. We consider these explanations in relation to data from causal- and reward-learning imaging experiments in first-episode psychosis patients. The findings suggest that a combination of these factors may resolve the question of why performance is sometimes preserved when brain patterns are disrupted.

Fig. 1.

Reward Prediction Error in Psychosis Patients, Revealing Activation in Bilateral Ventral Striatum and Medial Prefrontal Cortex (P < .005 Uncorrected, Minimum Cluster Size 10 Voxels). See online supplementary material for a color version of this figure.

Fig. 2.

During Causal Learning, Better Performing Patients More Strongly Activate the A Priori Network of Interest of Head of Caudate and Right Prefrontal Cortex Compared With Worse Performing Patients (P < .005 Uncorrected). See online supplementary material for a color version of this figure.

Fig. 3.

Equivalent Learning Rates in First-Episode Psychosis Patients and Control Subjects During Causal Learning. Error bars represent SEs.

Fig. 4.

Behavioral Results for Reward Learning. Left panel shows that although control subjects made more correct choices than patients, this difference was not statistically significant. Right panel shows an adaptive reinforcement-related speeding effect in control subjects (faster responses on reward trials) and a significant attenuation of this effect in patients. Moreover, patients were significantly faster than control subjects on the irrelevant, neutral condition. Error bars represent 95% confidence intervals.

Fig. 5.

Regions in Which Better Performing Patients Activate More Strongly Than Worse Performing Patients, Masking Out Areas Activated by Control Subjects, So Indicating Patient Specificity. Upper and middle panels show causal learning; lower panels show reward learning (P < .005). The contrast identified regions that differentiate better from worse performing patients more than they differentiate better from worse performing control subjects, masked inclusively by better learning patients greater than worse performing patients and masked exclusively by better learning control subjects greater than worse learning control subjects. See online supplementary material for a color version of this figure.