Disturbances of the minimal self, characterized by abnormal sense of the body, body ownership and agency have been proposed as the phenomenological phenotype of schizophrenia. However, self-disturbances have not been extensively investigated, in part, due to the subjective nature of such processes, and the associated difficulty of studying these phenomena using empirical methodology. Of 115 potential studies on self-awareness in schizophrenia, a total of 25 studies met the inclusion criteria for the meta-analysis comprising 690 patients with schizophrenia and 979 healthy controls. We calculated Hedge's g to obtain a better estimate for the standardized mean difference in small samples. We identified significant basic self-disturbance in schizophrenia, as compared with healthy controls (25 studies, effect size=0.51). Additional comparison of three sub-categories of the sense of body ownership (4 studies, effect size=0.91), the sense of agency (15 studies, effect size=0.49), and self-reported subjective experiences (6 studies, effect size=0.57) also confirmed group differences. The complete set of 25 studies, and the studies in the sub-categories showed the statistical homogeneity of the characteristics. After a correction for potential publication bias using the trim-and-fill method, the main findings for all studies combined remained significant. Overall, patients with schizophrenia showed deficits in the sense of the minimal self, driven by abnormal sense of body ownership and sense of agency. Interestingly, the disturbed sense of agency in schizophrenia suggests an exaggerated self-consciousness rather than a diminished sense of self. Further research that utilizes sophisticated study designs is needed to examine the nature of self-disturbances in schizophrenia.
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