Author: Chelsea Reynolds
Reynolds, Chelsea, 2019 Searching for intelligence in the sleeping brain: The relationship between adolescent sleep spindles and cognitive performance, Flinders University, College of Education, Psychology and Social Work
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Sleep spindles are short bursts of oscillatory brain activity during sleep, which have shown positive relationships with measures of intelligence and cognition in adults. Less is known about this phenomenon in adolescence, however. Adolescence is a period of change, with the onset of puberty, development of higher-order cognitive functions and brain maturation coinciding with the pressure to perform well in high school. Adolescents also experience changes to their sleeping patterns, which typically involves later bedtimes, difficulty waking in the morning for school, and an overall loss of sleep. This thesis aimed to add to the literature by investigating the relationship between adolescents’ spindles and cognition, and to determine whether the state factor of sleep restriction and the trait factor of development influence this relationship.
Following an introduction to adolescents’ sleep patterns and sleep spindles (Chapter 1), a systematic review and meta-analysis (Chapter 2) investigated the relationship between spindles and cognitive performance in adolescent samples. Adolescents’ spindles showed moderate positive associations with fluid IQ (r = 0.44), working memory/executive function (r = 0.40) and speed/accuracy (r = 0.33), while full IQ/verbal IQ was not significantly associated (r = -0.05). These findings set up expectations for the following chapters.
A second major aim of the thesis was to determine what happens to adolescents’ spindles and their relationship with cognition during sleep restriction, using a dose-response design (5hrs vs 7.5hrs vs 10hrs’ time in bed) (n = 34). Firstly, the reliability of adolescent spindle characteristics was established in the control condition (10hrs), with slow spindle amplitude and fast spindle density, duration and amplitude showing good reliability with a single night of sleep recording, while 2 nights were required for slow spindle duration and 4 nights for slow spindle density (Chapter 3). Secondly, adolescents’ spindles showed significant changes during severe sleep restriction (5hrs), where fast spindle amplitude became lower and fast spindle duration became longer (Chapter 4). Lastly, spindles were not significantly associated with cognitive performance at baseline, nor was the change in spindle activity during sleep restriction related to changes in cognitive performance (Chapter 5). A potential protective function of spindles was revealed, however, where adolescents with longer spindles at baseline experienced less deficits to sustained attention during severe sleep restriction. Adolescents’ spindles were therefore affected by sleep restriction, however the association between spindles and cognition was unclear.
The third major aim of the thesis was to investigate the developmental changes of spindles in a longitudinal study of early adolescents (n = 20). Fast spindle frequency showed a significant increase across an 18-month period, and slow frequency showed a similar pattern, confirming past findings, however changes to other spindle characteristics were not yet evident (Chapter 6). Again, spindles did not show significant associations with cognitive performance, and the changes in spindles over time were not meaningfully related to changes in cognition over time (Chapter 7). Spindles therefore showed some developmental changes in early adolescence, however were not related to cognition.
Overall, adolescent sleep spindles are impacted by both state (sleep restriction) and trait (development) factors, adding to the current literature and providing theoretical and clinical implications (Chapter 8). The associations between spindles and cognition seen in previous studies, however, were not replicated. Future investigations are encouraged to combine data sets to comprehensively investigate this phenomenon, and longitudinal studies with an extended time-base would add to the understanding of the development of spindles and cognition in adolescence.
Keywords: sleep spindles, adolescence, cognitive performance, intelligence, development, EEG, sleep restriction
Subject: Psychology thesis
Thesis type: Doctor of Philosophy
Completed: 2019
School: College of Education, Psychology and Social Work
Supervisor: Michael Gradisar