Negative symptoms and cognitive deficits: what is the nature of their relationship?

Negative symptoms and cognitive deficits in schizophrenia share many features and are correlated in their severity on a cross-sectional basis. The question arises as to the nature of this relationship: are these symptoms the same, caused by the same factor (or factors); or is the nature of their relationship determined by other factors, such as definitional issues and common correlates? In this article we provide a conceptual overview for addressing this question and provide a selective review of the literature on the cross-sectional and longitudinal relationships between these two features of the illness. We describe 4 different models of the "true" relationship between these variables. Some data suggest that the relationship between these variables is determined by the definition of negative symptoms employed and that, in general, the correlation is moderate at the most. Further, path modeling suggests the possibility, to be addressed with later research, that correlations between negative and cognitive symptoms and everyday functional outcomes may influence the observed correlations between these variables. Thus, we conclude that negative and cognitive symptoms may be separable, if not conceptually independent, domains of the illness and that it might be possible to develop treatments that target negative symptoms and cognitive deficits independently.