Doctoral dissertation

Anna-Liisa Satomaa: Neurophysiological Features of Sleep in Infants: Visual and Computational Approach

Anna-Liisa Satomaa
In infancy, sleep reflects the development of the central nervous system (CNS). Accordingly, the quality and quantity of sleep are known to be consequential for the future development and well-being of infants. In addition to uncovering the basic physiology of sleep, the objective of infant sleep research is to advance knowledge of the typical development of sleep and to facilitate the early recognition of abnormality. M.D. Anna-Liisa Satomaa studied in her doctoral dissertation the neurophysiological features of sleep in infants.

Ultimately, the increasing knowledge can be used to refine timely and proportionate interventions.

The infant sleep literature is infamous for the variability of the sleep parameters published. In the recent decades, the vast majority of sleep research has been based on polysomnography (PSG), which is considered the gold standard of sleep studies. PSG is a multi-channeled continuous recording during sleep that comprises EEG and auxiliary channels for the sleep stage differentiation, and a set of further physiologic signals that measure, for example, the respiratory function.

Traditionally, the differentiation or scoring of the sleep stages is performed visually according to specific visual scoring rules, and it is likely that the considerable diversity of the sleep scoring rules and methods promote variability in the reported values. Regarding the inter-individual differences, the rapid development of the CNS and the age- dependent transformation of sleep it entails surely augment the diversity still further.

Because of the large variability, the conventional sleep architecture cannot be used to detect abnormality apart from in extreme cases. Furthermore, the basic analysis of sleep architecture lacks the topographical and frequency domain resolutions. In order to uncover the topographical nuances in the sleep features, contemporary sleep research employs quantitative methods of sleep analysis.

Indeed, sleep is not homogenous across the convexity. Instead, the quantitative features of sleep EEG are modulated by the local and global regulations of sleep. The regulatory processes depend on the duration of wakefulness, the time of the day, and the amount of stress a cortical area has endured during wakefulness.

Importantly, in children, the topographical properties of the sleep EEG activity depend on the topical stage of cortical maturation, which is known to progress from the posterior areas towards the anterior with age. Furthermore, the quantitative EEG features are known to associate with intelligence in adults, and with the various domains of psychomotor development in children. However, the younger the children, the less the local features of sleep have been studied. In infants, the knowledge of the computational characteristics of sleep and their associations with the psychomotor development is particularly scarce.

This dissertation focuses on the issues of comparability in the young infants´ conventional PSG studies. The present work highlights the importance of scrutinizing the methodology underlying the values presented in the infant sleep literature. Intuitively, the use of uniform sleep scoring rules and standardized methodology will help to improve comparability among sleep studies. Recently, the standardized scoring criteria for young infants became available, and in the past few decades, the technical obstacles delimiting the choice of the recorded PSG channels have been overcome. Consequently, the future of comparability looks brighter.

Furthermore, the findings of this dissertation add to the body of knowledge of computational, local, and age dependent sleep quality in infancy. Many of the findings were attributable to age-dependent brain maturation in agreement with the findings of previous studies. However, the infants tended to present inter- hemispheric differences in their sleep parameters, an observation which has been rarely reported in the past. For the moment, the physiological significance of these findings can only be speculated, based on general knowledge of functional brain anatomy, but they contribute to a more solid view of developing sleep, and will surely help in the design of future studies.

In addition, in the present work, the associations of the computational sleep parameters with the eight-month-old infants´ psychomotor development were studied. The associations have not been studied in infants this young before, and while the fundamental origins of the associations found warrant further research, the present work stresses the careful consideration of the studied frequency ranges, the topography of the analyses, and the timing and duration of the sleep recordings.

The doctoral dissertation of M.D. Anna-Liisa Satomaa in the field of Clinical Neurophysiology titled Neurophysiological features of sleep in infants: visual and computational approach will be publicly examined at 12 o'clock on Friday 17 September 2021 at the Faculty of Medicine and Health Technology of Tampere University. The venue is Arvo building auditorium F114, address: Arvo Ylpön katu 34. Docent Leena Lauronen from University of Helsinki will be opponent while Professor Sari-Leena Himanen will act as the custos.

The event can be followed via remote connection.

The dissertation is available online at
http://urn.fi/URN:ISBN:978-952-03-2021-8

 

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