Neurocognitive indicators of clinical high-risk states for psychosis: a critical review of the evidence.

The present review investigates the empirical evidence from cross-sectional and long-term follow-up studies on neurocognitive indicators of an increased risk for developing schizophrenia spectrum psychoses in clinically defined high-risk samples. First, the investigations at the Cologne center for early recognition and intervention are briefly summarized and then integrated within the available literature. Thirty-two studies with original data could be identified by extensive literature search. Cross-sectional investigations of neurocognitive baseline assessments in high-risk samples with unknown conversion status have produced rather inconsistent results. Nevertheless, most convincing evidence could be collected for abnormal functioning in processing speed measures (digit symbol coding, Trailmaking Test-B, Stroop Color Naming), the Continuous Performance Test, verbal working memory measures, verbal memory and learning, and verbal fluency, though negative findings have also been reported in every instance. Moreover, high-risk subjects were found to perform both at the schizophrenia performance level and at a close to normal level. Longitudinal follow-up assessments provided predictive evidence with regard to psychosis conversion for measures of processing speed and of verbal memory and learning. However, a substantial number of negative findings does not allow for straight-forward conclusions. Finally, some reasons for inconsistent findings are discussed critically speculating on demographic differences, reliability and sample sizes, and conceptual imprecision in communicating results.