PhD Oral Exam - Nyissa Walsh, 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

Chronic insomnia is a growing public health concern that impacts more females than males and is associated with heightened risk for various chronic health conditions. Sleep disturbances such as chronic insomnia contribute both to the risk of these chronic health conditions but also represents a core symptom that impacts their development, maintenance, and recurrence. This manuscript-based thesis examines how biological sex, insomnia, and aging interact to shape sleep physiology, with a focus on neural oscillations during non-rapid eye-movement (NREM) sleep. Despite well-established sex differences in insomnia prevalence and severity, the neural mechanisms underlying these differences remain poorly understood. This represents a critical gap in the literature, particularly given that sleep microarchitecture is closely linked to brain health, cognition, and overall well-being. In Chapter II, this thesis first synthesizes existing evidence on sex differences in the sleep microarchitecture of healthy individuals and those with insomnia. It sheds light on a female advantage in neural oscillatory sleep activity in healthy populations and highlights substantial limitations in sex-specific analyses in insomnia research. As a result, in Chapter III, this dissertation provides novel empirical evidence demonstrating that age alone does not account for variability in sleep-related neural mechanisms. Rather, insomnia and biological sex each uniquely contribute to alterations in NREM oscillatory activity, suggesting that different pathways underlie sleep disruption across individuals. Importantly, the findings across Chapter III and IV indicate that males and females with insomnia exhibit distinct patterns of sleep physiology and symptom expression, supporting the presence of sex-specific insomnia phenotypes. This dissertation emphasizes the importance of studying the multi-dimensional nature of sleep difficulties to fully capture the difficulties males and females uniquely experience with insomnia. In Chapter IV, while we found that current first- line treatments such as cognitive behavioural therapy for insomnia (CBT-I) are broadly effective across sexes, they may not fully address underlying neurophysiological differences. Overall, this thesis advances our understanding of sleep as a biologically and clinically heterogeneous process, emphasizing the need to move beyond one-size-fits-all models of insomnia. By identifying sex-specific mechanisms of sleep disruption, this work highlights sleep microarchitecture as a promising target for more personalized and mechanistically informed assessments and interventions, with potential implications for improving sleep health and alleviating subsequent cognitive and mental health outcomes.