Neuropsychology of reward learning and negative symptoms in schizophrenia

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Abstract

We used the Iowa Gambling Test (IGT) to examine the relationship of reward learning to both neuropsychological functioning and symptom formation in 65 individuals with schizophrenia. Results indicated that compared to controls, participants with schizophrenia showed significantly reduced reward learning, which in turn correlated with reduced intelligence, memory and executive function, and negative symptoms. The current findings suggested that a disease-related disturbance in reward learning may underlie both cognitive and motivation deficits, as expressed by neuropsychological impairment and negative symptoms in schizophrenia.

Introduction

Disruptions in learning and motivation have long been viewed as central to both neuropsychology and symptom formation of schizophrenia. Indeed, neuropsychological studies frequently have revealed widespread deficits with most pronounced impairments in declarative memory as well as executive attentional function, each of which may reflect dissociable disturbances with distinct pathophysiology (Cannon et al., 2000, Nestor et al., 2004, Nestor et al., 2008). Likewise, both negative and positive symptoms are defining features of schizophrenia, with the former characterized by diminished levels of motivation, emotional expressivity, social engagement, and social attention, and the latter by delusions, hallucinations, and thought disturbance (Andreasen et al., 1992). However, whether positive and negative symptoms reflect a common or different underlying pathophysiology remains an open question (Crow, 1980).

Here we used the Iowa Gambling Test (IGT), a standardized measure of motivated decision making to probe the dynamics of reward learning (e.g., Bechara et al., 1994) in schizophrenia (e.g., Sevy et al., 2007). Findings from fMRI studies (e.g., Preuschoff et al., 2008) have suggested that this learning relies heavily on prediction error processes; expectations are generated from extracting the ambiguous probabilities of the four card decks, which comprised the IGT, and these can be tested against the actual result of each selection. Outcomes that violate expectancies facilitate learning by capturing attention (e.g., Mackintosh, 1975). Hence, the veridical capacity to detect a mismatch between expectations and actual outcome, that is to recognize a prediction error and to adjust subsequent choices, accordingly, may very well represent an important information-processing mechanism underlying performance on the IGT. We predicted that schizophrenia will be associated with impaired reward learning, as assessed by the IGT, which will be associated with disease-related reductions in intelligence, executive functioning, and declarative memory, as assessed by neuropsychological tests, and in motivation, as assessed by negative symptom ratings.

Section snippets

Method

Research participants were between the ages of 17 and 55 years, right-handed, native speakers of English, without histories of ECT, neurological illness, and without alcohol or drug abuse in the past 5 years. All research participants gave informed consent prior to their participation in the study. Diagnoses for patient group were ascertained by the Structured Clinical Interview for DSM-IV Axis I Disorders—Patient Edition (SCID-P), along with chart review. All patients were part of an ongoing

Results

Table 1 presents test scores on measures of intelligence, memory and executive function for the two groups. These scores were submitted to an analysis of covariance (ANCOVA), controlling for group differences in education. For the WAIS-III, in relation to the control group, the patient group scored significantly lower on WAIS-III full-scale, verbal and performance IQ measures, F (1,72) = 6.43. p = .013, Partial Eta Squared = .082. Likewise for the WMS-III, in relation to the control group, the

Discussion

In relation to controls, research participants with schizophrenia showed significantly reduced reward learning as measured by the IGT. This overall reduction occurred despite both groups showing similar performance over the first block of 20 IGT trials. Whereas for both groups IGT correlated with IQ, only for the schizophrenia group did reduced reward learning on the IGT correlate with memory and executive function and also with negative symptoms. In addition, the neuropsychological data

Role of funding source

This work was supported by the National Institute of Health (R01 MH 40799 and P50 080272 to RWM, RO1 MH 63360 to MN, RO1 MH50747, K05 MH 070047, and P50 080272 to MES), the Department of Veterans Affairs Merit Awards (RWM, JJL, MES), and the Department of Veterans Affairs Schizophrenia Center (RWM, MES).

References (16)

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