Neurocognition in first-episode schizophrenia: A meta-analytic review.

Compromised neurocognition is a core feature of schizophrenia. Following Heinrichs and Zakzanis's (1998) seminal meta-analysis of middle-aged and predominantly chronic schizophrenia samples, the aim of this study is to provide a meta-analysis of neurocognitive findings from 47 studies of first-episode (FE) schizophrenia published through October 2007. The meta-analysis uses 43 separate samples of 2,204 FE patients with a mean age of 25.5 and 2,775 largely age- and gender-matched control participants. FE samples demonstrated medium-to-large impairments across 10 neurocognitive domains (mean effect sizes from -0.64 to -1.20). Findings indicate that impairments are reliably and broadly present by the FE, approach or match the degree of deficit shown in well-established illness, and are maximal in immediate verbal memory and processing speed. Larger IQ impairments in the FE compared to the premorbid period, but comparable to later phases of illness suggests deterioration between premorbid and FE phases followed by deficit stability at the group level. Considerable heterogeneity of effect sizes across studies, however, underscores variability in manifestations of the illness and a need for improved reporting of sample characteristics to support moderator variable analyses.