A Neuroimaging Perspective of Schizotypy

Abstract

Schizotypy is a useful construct for examining the developmental pathway(s) of schizophrenia-spectrum psychopathology. It unifies a wide spectrum of behaviour, ranging from normal personality traits to full-blown psychosis, thereby offering a framework in which the aetiology, development, and expression of schizophrenia-related disorders may be studied in conjunction with typical behaviour. Furthermore, the dimensional nature of the construct allows for investigations into the possible endophenotypes of schizophrenia and other related disorders, which may be used to distinguish those at a high risk of developing psychopathology from the general population. Various behavioural, cognitive, and neuroimaging studies have investigated the role of schizotypy on perception and cognition, most of which have found subtle abnormalities that are qualitatively similar to the deficits observed in schizophrenia patients. However, there is a need for a clarification of the construct and a more defined placement of nonclinical schizotypy on the spectrum, as there is a lack of consistency in the measurement, definition, and effects of schizotypy on nonclinical populations. Towards this end, the overall aim of the current thesis was to investigate schizotypy using multiple behavioural and neuroimaging methods within the same sample of participants, in order to build a more comprehensive profile of a nonclinical individual with schizotypal personality. Study 1 revealed that early sensory gating abnormalities are present in those with high levels of schizotypy, establishing that lower sensory processes are affected in individuals who may be predisposed to psychopathology, and may contribute to higher-level cognitive deficits observed in those with schizophrenia. In Study 2, we examined the relationship between language laterality and schizotypy, and found that cerebral laterality in the current sample did not differ on the basis of levels of schizotypy. This suggests that reduced laterality is not an indication of schizotypal thinking, especially in high-functioning, young adults. Study 3 demonstrated that schizotypy may result in adaptive cognitive characteristics, as evidenced by the increased level of figural creativity seen in the schizotypal individuals. There were no group differences in the verbal creativity measure. Finally, Study 4 found neuroanatomical differences in high schizotypy, where grey matter volume reductions indicate that structural abnormalities are present even in the absence of high functional deficits. Broadly and taken together, these findings contribute to the evidence of a multidimensional construct of schizotypy. They further lend support to the body of work suggesting that the schizotypy-schizophrenia spectrum shares similar functional processes, possibly arising from the same underlying structural deficits. Finally, schizotypy provides an integrative framework in which the complex interactions between the gene and environment should be studied in order to further characterise both the adaptive and maladaptive manifestations of schizotypal behaviour.