Salience and motivated behaviour in schizophrenia

Schizophrenia is a long-term psychotic disorder that affects approximately 1% of the population worldwide. Schizophrenia is characterised by negative symptoms, such as anhedonia and social withdrawal, and positive symptoms, such as hallucinations and delusions. The impact of schizophrenia reaches beyond the impaired social and cognitive function of the individual, affecting families and wider communities. Therefore, despite its low prevalence, there is a long history of multidisciplinary research investigating the causes of schizophrenia. The effect of antipsychotics in reducing the intensity of symptoms, through their antagonistic effect on dopamine, has led to dopaminergic based theories of schizophrenia. One such theory is based on aberrant salience, the assignment of importance to stimuli that have no intrinsic or learned value or salience. The aberrant salience hypothesis links hyperdopaminergic activation to symptoms of schizophrenia through the intermediary effect of motivational salience. Specifically, it is proposed that hyperdopaminergic activation in schizophrenia creates an aberrant motivational association with a stimulus, leading to cognitive explanations for the unexplained importance that contribute to the development of symptoms. Behavioural and neural evidence supports heightened aberrant salience in schizophrenia, although specific measures of aberrant salience have yielded inconsistent results. There is also a large body of evidence suggesting cognitive functions anchored in dopaminergic activation, such as reward processing and motivated behaviour, are impaired in schizophrenia. To date, however, the assumption that motivational salience mediates the relationship between hyperdopaminergic activation and aberrant salience has not been tested. The current project sought to elucidate the relationship between aberrant salience and motivational salience. The convergent validity among measures of aberrant salience (Salience Attribution Task and Aberrant Salience Inventory) and motivated behaviour (Effort Expenditure for Rewards Task and Stimulus Chase Task) were investigated in undergraduates. To assess whether aberrant salience, and the underlying relationship with motivational salience, is unique to schizophrenia, the same measures were completed by individuals diagnosed with schizophrenia, experiencing symptoms of anxiety, or unaffected by mental health. Whereas schizophrenia was associated with heightened aberrant salience, the aberrant salience indices lacked specificity, sensitivity, and convergent validity. Furthermore, whereas schizophrenia was associated with maladaptive motivated behaviour, there was limited evidence supporting a relationship between measures of aberrant salience and motivational salience. The failure to find evidence of such a relationship may be due to issues with the aberrant salience measures or the underlying assumption that motivational salience mediates aberrant salience. Further research is needed to develop measures of aberrant salience that are anchored to known neural systems underlying salience processing