Identifying state and trait components of sensory and motor disturbances across the schizophrenia spectrum

Summary Sensorimotor dysfunction is frequently observed in people with schizophrenia as well as their unaffected relatives, which has led to proposals that these disturbances represent a vulnerability (or trait feature) of the disorder. However, there are reports that sensorimotor signs may also represent state features. This study will examine the heterogeneity of sensorimotor dysfunction across the schizophrenia-spectrum by identifying unique and causal links between specific sensorimotor signs and trait and state features of psychotic illness.

Project Details

Subtle motor and sensory abnormalities, or neurological soft signs (NSS), are frequently reported in schizophrenia. Such abnormalities have been reported at different stages of the illness, including in individuals at risk for psychosis, first-episode psychosis and chronic schizophrenia, as well as healthy first-degree relatives of individuals with the disorder. This has led to proposals that NSS represents a vulnerability, or trait, marker of the disorder, possibly as a result of early disturbances to brain function.

Despite this ‘trait’ conceptualization of NSS in schizophrenia, there are several observations that are at odds with this clinical picture. Firstly, sensorimotor dysfunction like NSS are not specific to psychotic disorders such as schizophrenia, being present across a number of psychiatric and neurodevelopmental disorders such as autism and mood disorders. NSS are also reported to fluctuate over the course of schizophrenia and co-vary with a person’s clinical symptoms, with decreases in some NSS associating with clinical improvement. These observations suggest that NSS may have a ‘state’ and/or ‘transdiagnostic’ component, which is at odds with the trait and neurodevelopmental perspective.

It is possible that these contradictory findings are due to the heterogeneity of NSS, with some signs representing a trait, or neurodevelopmental marker, and others being state markers, fluctuating with level of symptoms. However, there are few studies that have parsed the heterogeneity of NSS in relation to trait and state markers across the schizophrenia-spectrum.

The aim of this study is to identify which aspects of NSS are linked to trait features of schizophrenia or neurodevelopment and which are linked to state features. The heterogeneity of NSS will be interrogated by use of network models, which can graphically represent complex patterns of relationships between variables. Network models can identify cyclic, causal or reciprocal relationships between individual items, and identify items that might be central or most influential to other items. These models have important implications for understanding unique and causal relations between individual variables. In the current project the network will consist of individual items of the NSS and various trait, neurodevelopmental and state measures based on the existing literature. These features might consist of factors understood to be determined by genetic and early development such as brain gyrification and premorbid IQ, as well as symptoms, cognition and medication. This network model of NSS will be performed on three independent samples consisting of people at various stages along the schizophrenia or psychosis syndrome; 1) a cohort of individuals at clinical ultra-high risk of developing psychosis, 2) a large sample of individuals with established schizophrenia, and 3) a cohort of individuals with treatment-resistant schizophrenia.

Key research questions are to understand reciprocal, causal and unique links between specific sensorimotor processes and clinical, cognitive, and brain-based measures.

The student will be responsible for the development of the proposal and refinement of study hypotheses, conducting a literature review, data cleaning and performing statistical analyses. Publication of results is expected at the end of the project.