Abstract
There is a growing support for the conceptualisation of psychopathological symptoms as continuous and dimensional with underlying transdiagnostic mechanisms. Neuroticism has been identified as a transdiagnostic candidate with particular relevance to mood and anxiety disorders. As such, this thesis explored neuroticism in two highly burdensome diseases in this bracket, major depressive disorder (MDD) and generalized anxiety disorder (GAD). Though a transdiagnostic approach can provide rich understanding, a purely dimensional system has been criticised as reductionist. Therefore, this thesis also explored self-reflection and defensive behaviour as additional lower-level factors in MDD and GAD, to examine potential disorder-specific characteristics in a multi-factor approach to disease.
This thesis firstly explores the practical applications of neuroticism as a transdiagnostic factor, piloting a research recruitment tool using self-reported neuroticism to identify individuals with GAD in chapter 3. Neural activation and individual differences in defensive behaviour was explored in chapters 4 and 5, the latter using a sample of individuals with GAD to additionally attempt a pharmacological validation of a human translation of a rodent measure of fear and anxiety. Self-reflection was explored in chapter 6 through the lens of self-criticism and self-perception, as measured by a novel adaptation of a pre-existing tool. Finally, chapter 7 takes these findings beyond MDD and GAD, contextualising neuroticism in the vulnerable dark triad (VDT) of personality.
The results of this thesis indicate support for neuroticism as a transdiagnostic factor in MDD, GAD and co-morbidity of these disorders. Neuroticism appears to play a role in maladaptive characteristic expression, as demonstrated by involvement in self-criticism levels across these disorders; further neuroticism as the ‘core; of the maladaptive VDT was supported, though findings also indicated that other traits such as agreeableness are likely important. Interestingly, a potential adaptive role for average levels of neuroticism in healthy controls was identified, through a positive association with self-reassurance. Different characteristic expression of self-hatred and self-reassurance were shown in co-morbidity and GAD respectively, highlighting the relevance of lower-level factors in dimensional and transdiagnostic approaches to psychopathology. Identification of anterior insula activation during defensive behaviour was a key finding of this thesis and is discussed in the context of a neural network for transdiagnostic factors in MDD and GAD. The thesis also provides the first systematic review of active defensive behaviour in humans, the findings of which support animal models and prominent theories of defensive behaviour.
| Date of Award | 1 Jun 2019 |
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| Original language | English |
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| Supervisor | Adam Perkins (Supervisor), Steven Williams (Supervisor) & Allan Young (Supervisor) |