Recently, Dr. Raymond Chan and his team at the Neuropsychology and Applied Cognitive Neuroscience Laboratory, and key Laboratory of Mental Health of the Institute of Psychology, have undertaken a meta-analysis of NSS in patients with schizophrenia and healthy controls. This meta-analysis has shown, for the first time that neurological soft signs occur in a majority of the schizophrenia patient population and are similar to or exceed psychophysiological, cognitive and neuroanatomic findings as indicators or correlates of schizophrenic illness.

Neurological soft signs (NSS) are hypothesized as candidate endophenotypes for schizophrenia, but their prevalence and relations with clinical and demographic data are unknown. Conventionally, NSS are defined as non-localizing abnormalities without diagnostic specificity, but are crucial to the observable defects in sensory integration, motor coordination and inhibition. However, evaluating the strength of evidence in support of neurological soft signs as key indicators of psychotic illness has been complicated by a number of potentially confounding variables including duration of illness, medication doses, and the use of different measurement techniques.

In the present study, a systematic search was conducted for published articles reporting NSS and related data using standard measures in schizophrenia and healthy comparison groups. Potential moderator variables evaluated included age of patient samples, level of education, sample sex proportions, medication doses, negative and positive symptoms. The findings show that a large and reliable group difference (Cohen’s d) indicated that, on average, a majority of patients (73%) perform outside the range of healthy subjects on aggregate NSS measures. Significant relationships were found between NSS-total and both total and negative symptoms, with shared variances of 10-12%. In contrast, while confidence intervals for the mean value for NSS-Total and positive symptoms excluded 0, the effect size was relatively modest with less than 4% shared variance. Neurological soft signs occur in a majority of the schizophrenia patient population and are largely distinct from symptomatic and cognitive features of the illness.

This study was financially supported by National Science Foundation of China, 973 Program, and The Knowledge Innovation Project of the Chinese Academy of Sciences.

Fig.1. Funnel plot for the meta-analysis of differences in Neurological soft signs total scores between schizophrenia patients and healthy controls

This study is now published online in Schizophrenia Bulletin:
Chan, R. C. K.*, Xu, T., Heinrichs, R. W., Yu, Y., Wang, Y. (2009). Neurological soft signs in schizophrenia: A meta analysis. Schizophrenia Bulletin, doi.10.1093/schbull/sbp011 (IF: 5.843)