INTRODUCTION: (Study A) Trauma-Related Nightmares (TRNs) are a core feature of Post- Traumatic Stress Disorder (PTSD). We explored linguistic and somatic-experience differences between self-reports of trauma and those of nightmares related to the trauma. (Study B) Neurotic personality features are associated with many psychological disorders, including PTSD. Based on this relationship, we explored whether neuroticism predicts the rate of nightmares and bad dreams as well as the number of replicative nightmares (TRNs similar or exactly like their traumatic experience), above and beyond PTSD severity. METHODS: (Study A) Seventeen participants with varying severity of PTSD symptoms reporting recurring TRNs (mean age 27.47 years, SD = 10.33, 14 females) recalled a traumatic experience and nightmares related to that trauma. Trauma reports were written by participants, while nightmare reports were transcribed from audio recordings made as they were recalled following nightmares. Following both types of reports, participants indicated co-occurring somatic experiences by choosing from a list of 51 selections. Choices were later grouped into cardiovascular, respiratory, interoceptive, and tension categories. Linguistic content was measured using the Linguistic Inquiry and Word Count (LIWC) program and positive emotion, negative emotion, and somatosensory category words were totaled. Since trauma reports had significantly higher word counts than TRNs (p=0.0495), LIWC categories were normalized for total word count. Total and symptom- cluster severities of PTSD were assessed using the PTSD Checklist for DSM-5 (PCL-5). Wilcoxon Signed-Rank Tests and Spearman Correlations were used for statistical analysis, as Shapiro-Wilk tests showed that data were non-normally distributed. (Study B) 126 participants who had experienced a traumatic event within the past two years were recruited (mean age 24.13 years, SD = 4.994, 69% female) and, for an average of 14.89 nights, completed a dream questionnaire on which occurrence of nightmares (causing awakening) and bad dreams were reported and ranked based on their similarity to their recent traumatic experience. PTSD symptoms were assessed using the PCL-5 and personality features such as neuroticism were measured using the NEO Personality Inventory Revised (NEO PI-R), a questionnaire based on the Five Factor Model of personality. The combined number of nightmares and bad dreams was divided by the total number of nights reported and expressed as a rate, while a replicative nightmare count was generated by summing “similar to traumatic experience” and “exactly like traumatic experience” ratings. Hierarchical regressions were used to determine whether neuroticism predicted the rate of nightmare and bad dreams as well as the number of replicative nightmares above and beyond PTSD severity. Pearson correlations were used to check for relationships between variables and possible collinearity. RESULTS: (Study A) There were significantly more somatic experiences of interoception (p=0.0084) and tension (p=0.024) in trauma vs nightmare reports. The intrusion cluster of the PCL-5 was associated with cardiovascular (rho=0.592, p=0.0156) and respiratory (rho=0.619, p=0.0109) experiences in trauma reports, and interoception (rho=0.718, p=0.0033) and tension (rho=0.556, p=0.0224) experiences in nightmare reports. (Study B) In two hierarchical regression models, neuroticism predicted neither nightmare and bad dream rate nor number of replicative nightmares over and above total or PTSD symptom cluster severity (p=0.596; p=0.886). Collinearity checks did demonstrate a moderate positive relationship between these variables (r=0.317, p<0.001). CONCLUSION: (Study A) More somatic experiences of interoception and tension were recalled from traumas than TRNs. Because the brain is deafferented from sensory input during dreaming, we expected, but did not find, state differences in other somatic experiences. Word categories in narratives also did not show state differences. Only the intrusion symptoms of PTSD predicted bodily sensations in trauma as well as TRN reports. (Study B) We found that neuroticism did not predict either nightmare and bad dream rate or the number of replicative nightmares above and beyond PTSD severity, when taking demographic factors into account. The positive correlation between PTSD and neuroticism could explain this lack of significance. SUPPORT: R21MH128619

This thesis aimed to extend the existing psychological and neural basis of social processing in Major Depressive Disorder. This investigation was an attempt to resolve current conflicts and gaps in the social affective neuroscience literature regarding social functioning in depression. Chapter 1 consisted of a general introduction to the current evidence-base and theoretical frameworks surrounding social processing more generally, and in depression more specifically. ‎Chapter 2 provided an exploration of the systemic behavioural biases in in those with depression compared to mentally healthy individuals using a range of social, affective and process measures implemented across the remaining chapters. Then followed a behavioural and neural investigation into self-relevant social processing in depression. Chapter 3 described the process of memory generation implemented across ‎ Chapter 4-6 using a script-driven paradigm. It further discussed the ecological validity of this paradigm using social autobiographical memories. Chapter 4 investigated the neural and behavioural responses to self-relevant autobiographical memories of social rejection and social inclusion in individuals with depression and in healthy controls. The next two chapters discussed the behavioural and neural basis of social processing in depression in response to others’ memories of social rejection and inclusion, using traditional and novel fMRI analysis methodologies in ‎Chapter 5 and ‎‎Chapter 6, respectively. The latter applied a novel intersubject correlation analysis to the same population of depressed and healthy controls as in Chapter 5. Then, Chapter 7 presented a future application of the script-driven imagery paradigm by investigating the effectiveness of different emotion regulation strategies in response to socially salient autobiographical memories in a population of healthy controls. Finally, Chapter 8 provided a general discussion bringing together behavioural and neural findings to provide a clearer understanding of social processing in Major Depressive Disorder. Current theoretical frameworks were used to guide the interpretation of these findings.