Sleep, memory, and the alcohol-exposed brain: investigating the relationship between SWS features, childhood hippocampal volume and declarative memory in young adults with fetal alcohol spectrum disorders

Tubaro, Julia

Sleep, memory, and the alcohol-exposed brain: investigating the relationship between SWS features, childhood hippocampal volume and declarative memory in young adults with fetal alcohol spectrum disorders

Thesis / Dissertation

2026

Publisher

University of Cape Town

Publisher

University of Cape Town

Department

Department of Psychology

Faculty

Faculty of Humanities

Abstract

Prenatal alcohol exposure (PAE) has detrimental effects on sleep and memory. Children with PAE have shown a) clear disruptions to sleep maintenance with some evidence pointing to altered slow-wave sleep (SWS) and b) deficits in short-term verbal memory recall, persisting into young adulthood, with some evidence of consolidation difficulties over this timescale. Furthermore, the hippocampus, a brain region crucial for memory encoding and facilitating sleep-dependent consolidation, is also negatively impacted by PAE. However, the connection between these abnormalities has not been explored despite the well-documented relationship between SWS, the hippocampus and memory consolidation. Given these known associations I aimed to investigate systematically, in a young adult population, 1) whether PAE was associated with differences in SWS architecture, childhood hippocampal volume and memory retention (a behavioural measure of consolidation) and 2) whether individuals with PAE (compared to those without exposure) with smaller hippocampi and altered SWS had poorer memory retention. Methods: Data from 76 young adults (21.68 years), from the Cape Town Longitudinal Cohort, were used from night two of a three-night sleep study. Participants were grouped as having fetal alcohol syndrome (FAS)/partial FAS; n = 24), non-dysmorphic heavily exposed (HE; n = 23) and healthy controls (n = 29). Participants completed evening and morning WRAML-II story and word-list tasks, separated by an 8-hour polysomnographically-recorded sleep interval. Maternal reports of PAE and hippocampal data were collected in earlier studies. Results: Individuals with a diagnosis of FAS/PFAS had more SWS arousals than controls (p = .018) and smaller left (p = .029; p = .008) and right hippocampi (p = .007; p = .006) than both HE and control individuals, respectively. Additionally, those with FAS/PFAS had poorer retention for the story task than controls (p = .021) with HE individuals trending towards the same pattern (p = .055). Results for dose-related exposure mimicked these results with higher exposure associated with poorer story retention (p < .001). Modelling revealed that dose-related PAE and fast spindle duration, coupling percentage and strength were important for predicting story-related information. Particularly, retaining contextual information relied on shorter fast spindles that coupled more frequently and less consistently. Greater coupling strength was only detrimental to story consolidation for individuals with smaller left hippocampi. Lastly, word-list retention was more strongly predicted by FASD status and SWS macro-architecture whereby only word-list retention for controls benefitted from more SWS. Conclusion: The findings link PAE to poorer sleep-dependent memory consolidation and suggest that PAE may disrupt the SWS-declarative memory relationship. For example, the typical benefit of greater coupling strength seems to have a paradoxical effect in those with smaller hippocampi, who are more likely to have PAE, suggesting a disruption in the mechanism of consolidation. The findings also provide novel insights into which aspects of SWS benefit the retention of contextual and discrete verbal declarative tasks. In the future interventions that target sleep can be developed to ameliorate memory deficits in this population and more specifically target micro-architecture for the learning of contextual information and macro-architecture for learning of discrete information.