Neurological soft signs (NSS) have long been observed in schizophrenia spectrum disorders and have been considered possible “target features” or endophenotypes. Substantial evidence has shown that NSS capturing motor coordination, sensory integration, complex motor sequencing and disinhibition are significantly and consistently increased in patients with schizophrenia compared to healthy controls across different stages of the illness. Recent imaging findings also provide strong evidence that NSS are associated with specific brain structural and functional connectivity deficits corresponding to clinical manifestations in patients with schizophrenia.

The brevity of NSS assessment (less than 10 minutes) makes it feasible for clinicians and researchers to screen for neurocognitive dysfunction in patients with schizophrenia. Recent findings have suggested that both NSS and conventional neurocognitive tests capture the same underlying brain functions that can be linked both at the microscopic (genetic components) and macroscopic (clinical syndromes) levels in schizophrenia spectrum disorders. However, all of these studies were limited to patients with a relatively long duration of illness and prolonged mediation exposure. It is possible that these findings were confounded by illness chronicity and medication effects.

Recently, Dr. CHAN Raymond from the Institute of Psychology, and his collaborators have examined the relationship between NSS and conventional neurocognitive functions in patients with first-episode schizophrenia. One significant distinction of the present study from previous ones is that this research adopted the invariance model in SEM to examine the temporal stability of the latent variables identified from NSS evaluation in a large sample of first-onset schizophrenia patients. This approach allowed researchers to remove the confounding effects of illness duration and medication exposure. This is the first study examining the temporal stability of NSS in a large sample of patients with first-episode schizophrenia.

A total of 157 patients with first-episode schizophrenia were assessed at baseline and 101 of them were re-assessed at six-month interval. A structural equation model (SEM) with invariance model across time was used for data analysis. This invariance model has an advantage of conventional SEM by providing a rigorous method to test measurement invariance and to examine the stability of the relationship between NSS and conventional neurocognitive functions across two time points. Findings showed that the model fitted well with the data at baseline assessment. Subsequent SEM analysis with invariance model at six-month interval also demonstrated the same stable pattern across time and showed strong measurement invariance and structure invariance across time. Also, findings suggest that neurological signs capture more or less the same construct captured by conventional neurocognitive tests in patients with schizophrenia. These results extend and replicate the previous findings on patients with established schizophrenia. The brevity and ease of administration of NSS assessment compared with conventional neurocognitive tests makes it a useful alternative for neurocognitive function screening in the clinical settings.

This study was supported by grants from the National Science Fund China Outstanding Investigator Award, the Strategic Priority Research Program (B) of the Chinese Academy of Science, and the Beijing Training Project for the Leading Talents in S & T.