|Embodiment deficits were central to early theories of schizophrenia and remain at the phenomenological core of the disorder. Contemporary evidence confirms disturbances of the bodily self as central to schizophrenia and suggests that they might be an early marker for psychosis-risk. This dissertation is comprised of three studies that examined embodiment in the schizophrenia spectrum to cast light on the nature and etiology of schizophrenia.
Given the role of interoception in embodiment and the lack of empirical research investigating interoceptive ability across the schizophrenia spectrum, in Study 1 we empirically measured interoception in individuals with schizophrenia (1A) and in relation to psychometric schizotypy (1B). We found that while individuals with schizophrenia have low interoceptive accuracy and report differences in the subjective experience of their interoceptive experiences, they have intact interoceptive awareness. No link was found between schizotypy and interoceptive functioning in the general population, which suggests that changes in interoception may only arise at the onset of psychosis. In Study 2, we used a topographical mapping tool to investigate emotional embodiment in relation to schizotypy. We found that individuals with high positive schizotypy experience embodied emotions with higher intensity but lower clarity and endorse more incongruent bodily sensations of emotions. Mirroring prior findings in individuals with schizophrenia, these differences were particularly notable for low arousal emotions. In Study 3 we investigated body ownership in relation to schizotypy and explored the role of the right tempo-parietal junction (rTPJ) in one’s sense of body ownership. We confirmed the link between positive schizotypy and the subjective experience of the Rubber Hand Illusion (RHI) and found a potentially protective role of negative schizotypy in strengthening body ownership. In the second part of this study, we failed to find an effect of rTPJ modulation on individual sensitivity to the illusion, which might reflect the limitations of the reductionist approach in the study of self-disorders.
Together, these findings suggest that some mild bodily disturbances (i.e., anomalous emotional embodiment and impaired body ownership), analogous to those observed in schizophrenia, are present in individuals with elevated levels of positive schizotypy.