Social and neuro-cognition as distinct cognitive factors in schizophrenia: a systematic review

Social cognition (SC) and neuro-cognition (NC) have emerged as predictors of functional outcome and possible endophenotype-markers in schizophrenia. The distinctiveness of these two domains is not well established. Factor analysis is used to identify distinct cognitive dimensions. This paper aims to systematically review studies reporting factor analysis of SC and NC in schizophrenia to provide empirical evidence for (a) distinctiveness of SC and NC; and (b) factor structure of SC. The review comprised 20 studies. Most of the studies were cross-sectional, involving variably defined 'stable' schizophrenia patients, using objective assessments of SC and NC. A quality check on reporting practices of factor analytic studies showed important deficiencies in reporting both exploratory and confirmatory factor analyses. There was fairly consistent evidence for the existence of distinct SC and NC factors, with eight out of nine studies supporting this separateness of the two cognitive dimensions. The results were inconsistent regarding factor structure of SC. Unitary, binary and multi-factorial constructs were reported, possibly due to variability and lack of comprehensiveness of the SC measures used. This review highlights distinctiveness of SC and NC dimensions in schizophrenia. It thus provides construct validity for cognition in schizophrenia and offers clues regarding the potential neural processes underlying these cognitive dimensions. Future studies exploring the factor structure of SC should be guided by more careful theoretical work and use comprehensive measures of SC in large homogeneous samples of schizophrenia patients.