Exploring social cognition and mirror systems in schizophrenia and bipolar disorder

Schizophrenia and bipolar disorder show some overlap in genetics, epidemiology and clinical features. Individuals with these disorders often have poor social and vocational functional outcomes and reduced quality of life, even during times of symptom remission. Social cognition comprises a number of processes including emotion recognition, empathy and theory of mind (ToM), and recent research has indicated that these skills may be reduced in schizophrenia and bipolar disorder, and contribute to their reduced function. Despite this, the exact nature of these social cognitive deficits, their impact on quality of life, and possible underlying neural substrates, have not yet been established in these disorders. One brain network implicated in social cognition is the mirror system, however, research into this system in schizophrenia or bipolar disorder has been very limited to date. The goal of this thesis was to better understand the nature and impact of social cognitive deficits in schizophrenia and euthymic bipolar disorder, and comprehensively assess mirror system function as a possible contributor to these deficits. In this thesis, I first assessed a number of aspects of social cognition (emotion recognition, empathy and ToM), as well as cognitive, clinical, and quality of life variables in a schizophrenia, euthymic bipolar disorder, and healthy control group. The three groups were then compared using two putative measures of mirror system function (EEG and TMS). I found a significant reduction in cognitive ToM in both disorders, with the addition of a deficit in the recognition of anger in the schizophrenia sample, indicating some likely shared underlying brain pathology but also disorder-specific differences. Quality of life was not related to these social cognitive deficits in this sample, possibly due to other mediating factors. There was some evidence for underactive mirror systems in euthymic bipolar disorder but not schizophrenia, however, mirror system function was not strongly related to any of the social cognitive measures utilised in this study. The findings of this thesis make a valuable contribution to the understanding of social cognition in schizophrenia and bipolar disorder, and challenge the proposed importance of mirror systems for social cognition. Our findings indicate that social cognitive deficits should be considered in assessment and treatment planning in schizophrenia and bipolar disorder. In addition, this thesis highlights the need for further research aimed at understanding the neurobiology and true impact of social cognitive deficits. It is hoped that this knowledge will lead to better treatments targeting these deficits at both neurophysiological and behavioural levels, and ultimately improve patient outcomes and wellbeing.