PhD Oral Exam - Jocelyn Fotso Soh, Psychology

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Eating disorders (EDs) are psychiatric conditions involving interactions between biological, psychological, and environmental factors. Childhood trauma is a well-established risk factor for EDs, yet the biological pathways through which childhood trauma may contribute to ED risk are not well understood. This thesis examined the potential neurobiological, psychological and immune mechanisms associating childhood trauma with EDs.

The first study was a narrative review of empirical and meta-analytical research examining childhood trauma, EDs, and biological alterations. The research indicated that childhood trauma is three times more prevalent among individuals with EDs compared to the general population and is associated with changes in brain structure and function, stress- and sex-hormone regulation, immune processes, and dopamine and serotonin signaling. Psychological factors, including negative affect and emotion dysregulation, may also mediate or moderate these associations. However, limitations in trauma assessment, small sample sizes, and the predominance of retrospective and cross-sectional designs restrict conclusions about causality.

The second study examined immune-cell indices in women with active AN (n=198), in remission from AN for at least one year (remitted AN; n=62), or no ED (n=92). We also had follow-up data in the AN active group following four months of specialized ED treatment. We found that women with active AN had higher CD4⁺ T-cell proportion and CD4⁺/CD8⁺ ratio and lower neutrophil proportion and neutrophil-to-lymphocyte ratios compared to women with no EDs. Values on immune-cell indices in the group that was remitted for at least one year were generally similar to those observed in the control group. Within the AN-active group, BMI but not childhood trauma or other clinical features was associated with immune-cell indices. We further observed that, after 4 months of specialized treatment, neutrophil granulocyte proportion and neutrophil/lymphocyte ratio normalized, whereas CD4+ T-cell proportion remained unchanged. Overall findings of study 2 showed that immune-cell alterations in AN may largely reflect the effects of malnutrition, with relative elevations in CD4⁺ helper T lymphocytes potentially representing an adaptive response that persists during early symptom improvement but normalizes following sustained remission.

Together, these findings support a biopsychosocial framework in which childhood trauma may contribute to ED vulnerability through interacting biological and psychological pathways. Immune alterations in AN may primarily reflect the effects of malnutrition and illness state rather than lasting dysfunction. Longitudinal, multimodal research is needed to clarify how childhood trauma interacts with biological and psychological pathways to influence the development and course of ED pathology.