Table of Contents:
Schizotypy designates characteristics that are also present to different degrees in the general healthy population. These characteristics can be expressed, for example, in the form of limited affect, unusual behaviour and superstitious beliefs. Some of the research assumes a continuum model, which sees the schizophrenic disorder as the endpoint of a continuous dimension. This assumption is supported by the findings of shared genetic and environmental risk factors. The same applies to the observation of the presence of higher schizotypal values in people at increased risk of psychosis and in relatives of people with schizophrenia. Previous studies on morphological correlations of schizotypy in healthy individuals showed, with partially inconsistent results, an involvement of structures associated with the schizophrenic disorder, such as the prefrontal cortex and the precuneus.
With this work a multimodal investigation was carried out with regard to the existence of morphological correlates of schizotypy. The MRI data of 673 healthy test persons were taken into account and was collected by the DFG research group FOR2107 in cooperation with the Universities of Marburg and Münster.
Schizotypal characteristics were measured using the SPQ-B questionnaire. In addition to an overall score, the SPQ-B questionnaire covers three dimensions of schizoytpy. Clinical diagnostics using SKID-1 interview served for validation. The cortex volume and surface structure were examined with CAT12 as part of the SPM software. In addition to the volume of grey matter, cortical thickness, gyrification and cortical complexity were investigated. FSL was used to obtain information from the DTI data. FA and RD served as a measure of the directionality and integrity of the white matter fiber tracts. Statistical analysis was performed using a general linear model as a voxel-wise correlation analysis. For the overall measure and the three facets, the hypotheses of a correlation of schizotypal features and the volume of dorsolateral and medial prefrontal areas and the precuneus, a correlation with the integrity of fiber connections in the frontostriatal system and an association with cortical folding in the lateral prefrontal cortex in healthy subjects were tested. The results showed a correlation between the directionality of white matter within the frontostriatal system and schizotypal personality traits. In this area there was a negative relationship between cognitive-perceptive schizotypy and FA, and a positive correlation between interpersonal schizotypy and FA. The overall SPQ-B score correlated exclusively negatively with FA predominantly in association fibers. There was a negative correlation between interpersonal schizotypy and the volume of grey matter in an cerebellar area on the left. The cognitive-perceptive schizotypy and the gyrification index in an area of the left inferior parietal lobe were positively linked. The investigation did not provide any evidence of a connection between schizotypy and the volume in prefrontal areas and the precuneus. The same applies to the possible connection between schizotypy and cortical folding in the prefrontal cortex, which is included in the hypotheses. Especially the structure of white brain matter seems to be linked to schizotypal personality traits. The contrasting associations with the directionality of frontostriatal fiber tracts could be a result of schizotypy constructs´ heterogeneity caused by the multitude of genetic and environmental factors involved. Assuming the existence of a continuum from schizotypal traits in healthy individuals to schizophrenic disorder, the results with a negative correlation between positive, disorganized schizotypy as well as the overall value and fractional anisotropy tend to be congruent with observations in schizophrenia. The results could support the idea of a change in the connectivity of white brain matter that is decisive for the development of a schizophrenic disorder. As a consequence, secondary, measurable volumetric changes in the area of the frontal lobe and the precuneus, possibly characterizing the onset of the disease, are conceivable. The results of this work could support the idea of a function of the cerebellum that is involved in emotion perception and mentalizing and thus goes beyond motor functions. The observed correlation between cognitive-perceptive schizotypy and gyrification index in the parietal lobe could result from a changed early childhood brain development with a genetic component. The long-term observation of the test persons makes sense for the detection of an actual conversion to schizophrenic disorder depending on the structural correlations of schizotypy shown in this work.