Objective Behavioural Characterization of Intrinsic Motivation in Schizophrenia: A Focus on Exploratory Behaviour and Activity Engagement

Motivation deficits are a prominent and pervasive feature of schizophrenia that substantially impacts psychosocial functioning. While task-based investigations have characterized these deficits within the purview of extrinsic motivation (driven by external rewards), similar evaluation of intrinsic motivation (in the absence of reward) has been lacking. This thesis describes the development and validation of two tasks that objectively quantify behaviours that align with distinct facets of intrinsic motivation. Exploratory behaviour (in a novel environment containing common and uncommon objects) and activity preference (between an activity requiring effortful engagement versus another experienced passively) in the absence of external incentive were quantified using wireless motion capture in an open-field setting. Initial task validation studies tested the hypotheses that outpatients with schizophrenia (n=21), compared to healthy controls (n=20), would demonstrate reduced exploratory behaviour and active engagement, and that task-derived behavioural measures would correlate with clinical measures of amotivation and psychosocial functioning. Concerted examination of performance in both tasks in an extended sample of patients (n=45) and controls (n=47) tested the hypotheses that multifaceted characterization of intrinsic motivation would reveal distinct behavioural phenotypes, and that these phenotypes would predict schizophrenia diagnosis, clinical amotivation, and psychosocial functioning. Most task-derived measures indicated nonsignificant between-group differences in the initial validation studies, but performance impairments correlated with more severe amotivation and poorer functioning in schizophrenia. Concerted examination of task performance via cluster analysis identified three behavioural phenotypes: low exploration, low activity, and high exploration/activity. The two low performance clusters disproportionately comprised patients with schizophrenia and demonstrated similar elevated amotivation levels. Patients demonstrated poorer functioning compared to within-cluster controls, with the discrepancy increasing from the high performance to low activity to low exploration cluster. These findings suggest that exploratory behaviour and activity engagement are valuable behavioural biomarkers of intrinsic motivation. Clinical amotivation may reflect impairment in separate, behaviourally distinguishable facets of intrinsic motivation. Impairment in either facet may be deleterious particularly for individuals with schizophrenia. In addition to demonstrating the feasibility of quantifying real-world human behaviours, these methods and findings stand to advance the conceptualization of motivation deficits in schizophrenia and may help guide personalized remediation.Ph.D