Abstract
Background: Those with and at risk for schizophrenia have highly sensitive stress responses. It is unclear whether this stress sensitivity is the result of a biological predisposition, or whether the sensitivity develops as a result of experiencing multiple major life stressors. The sensitization hypothesis proposes that those at risk for schizophrenia experience increased stress sensitivity following major life stressors. As a result they experience chronic stress, which can lead to brain changes that are associated with psychosis. If this process is related to the development of schizophrenia, then it should be evident in risk states. The aim of this thesis was to examine the sensitization hypothesis, in particular with regard to psychological stress sensitization. It was hypothesised that in undergraduate students psychological stress sensitivity would mediate the relationship between historical risk factors and schizophrenia risk, and that those at risk for schizophrenia would experience sensitization of psychological stress sensitivity scores across 6 months.
Method and Results: To examine these hypotheses, 4 main studies were completed. In the first study, the psychometric properties of an existing measure of daily hassles were examined to determine whether the measured construct reflected the incidence of transient stressors or trait reactivity to stress. The measure had a high test re-test reliability and high internal consistency, even when all commonly reoccurring items were removed, which was consistent with the idea it was measuring trait reactivity. Using this information, the Acute Hassles Scale (AHS) was developed as a measure of psychological stress sensitivity.
In the second study, the AHS was compared to multiple other measures of stress sensitivity (or other similar constructs). While the AHS appeared to be an appropriate measure of psychological stress sensitivity, it was not a useful measure of biological stress sensitivity. In the third study, the relationship between participants’ historical risk factors, and their schizotypy scores, and whether this relationship was mediated by stress sensitivity was examined. The relationship between risk factors such as general negative life events, socioeconomic status, parental antipathy, and sexual trauma were related to schizotypy and these relationships were mediated by stress sensitivity or stress coping scores. In the fourth study, longitudinally, it was examined whether major life events result in changes to stress sensitivity, and whether there was sensitization of stress responding evident for the risk groups over time. Sensitivity to stress was higher for those at high risk than those at low risk for all of the risk groups. The disorganised risk group showed significant sensitization over time, and cognitive- perceptual risk group showed a trend of sensitization over time. The interpersonal risk group showed evidence of the habituation of stress sensitivity over time, similar to the low risk groups.
Conclusion: These findings suggest that there may be different types of stress sensitivity, including reactivity and stress coping, and that these traits may mediate the relationship between some risk factors and schizophrenia risk. Furthermore, there is evidence that psychological sensitization may be involved as a process in schizophrenia risk in addition to biological sensitization.