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Sleep, Language Acquisition and Development

Understanding the downstream effects of early sleep for education and mental health (PI: Lisa Henderson, Funder: ESRC, Project blog)

Around 25% of children under three have sleep problems, such as difficulties getting to sleep and frequent night waking. Poor sleep during the early years has immediate consequences for behaviour and mood, as well as having a deleterious effect on parent health and family functioning; however, we have a relatively poorer understanding of how persistent early sleep difficulties are and whether they influence future outcomes such as school grades and mental health. Identifying whether and which early sleep difficulties impose a risk to later academic and mental health outcomes is of societal importance: Such research has the potential to reveal early risk factors for later academic problems and mental ill health that can be mitigated through raising awareness of the importance of sleep during this critical period and identifying routes to support. It would also further emphasize the need to provide guidance on sleep to early years providers, which is currently lacking.


There is some evidence that sleep difficulties can persist across development. There is also evidence that sleep quality and quantity in childhood predicts mental health and cognitive abilities in later childhood. However, methodological limitations prevent us from using these findings to inform policy on early sleep. For example, a lack of long-term longitudinal studies means that little is known about the effects of early sleep across childhood and adolescence. We have little understanding of the particular aspects of early sleep that persist over development and predict later sleep difficulties and real-world outcomes, such as diagnoses of mental illnesses and school grades. It is also unclear who is at heightened risk of poor sleep: previous research suggests that sleep is a particularly important driver of cognitive development in children from low socio-economic status backgrounds, but we do not know whether this is the case in the early years. Finally, although cognition and mental health are closely related, research investigating the effects of early sleep on these outcomes has done so in isolation. A much-needed integrative approach would allow us to examine the interactions between these variables, working to considerably advance our understanding of how early sleep affects later outcomes.


The current project will address these important gaps utilising existing large-scale longitudinal datasets. With these datasets we will address a number of key questions, such as do early sleep characteristics that emerge in the first three years of life predict sleep characteristics in later childhood and adolescence? Do early sleep characteristics predict later mental health, vocabulary, and educational outcomes? Does the extent to which early sleep characteristics predict later outcomes differ depending on socioeconomic status? What factors drive the relationship between early sleep and later educational outcomes (i.e., are there pathways from early sleep to vocabulary and emotional development that subsequently shape academic outcomes)?

 

 

The Underpinnings of Linguistic Optimisation in Comprehension (PI: Prof Gareth Gaskell, Funder: ESRC

It is now well-established that sleep, plasticity, and memory consolidation mechanisms are crucial for successful adult communication, particularly when a language involves a clearly novel item such as a new word. Recently, an intriguing addition to this literature opened up a new potential role for memory consolidation, this time moving beyond simple novelty. A recent study from our group suggested that sleep and memory consolidation may also operate to support everyday language comprehension even in the absence of new linguistic units. Here we comprehensively address whether and how these memory systems underpin comprehension. Three possible roles for sleep and memory consolidation in comprehension are considered here:

1) They help us to refine the mental representations of words to ensure optimal future comprehension.
2) They help us to track the linguistic events that are referred to during conversation, facilitating effective dialogue over a range of time-spans.
3) They help us to identify and maintain speaker-specific preferences in the way language is used.

All of these roles can be thought of as ways of optimising our ability to use language in conversation, or in reading and writing. Indeed any or all of these roles may turn out to be correct, and an exciting possibility is that at some level there might be a framework for unifying these disparate aspects of language comprehension based on the same underlying memory processes. The current proposal develops and tests these accounts, allowing us to understand for the first time the extent to which sleep and memory consolidation underpin and maintain our day-to-day ability to use language.

 

Memory Consolidation in Typical and Atypical Development (PIs: Dr Lisa Henderson and Prof Gareth Gaskell, Funder: ESRC

Sleep is known to affect the consolidation process that takes fragile memories and makes them robust. Components of sleep such as "slow oscillations" influence this consolidation process. However, little is known about how children's sleep may influence consolidation. This is important: children's sleep has more of the components that are crucial for consolidation of memory, and may show more substantial effects. Given that children encounter new information at a dramatic rate, it is important to understand what factors influence consolidation to ensure that learning is optimal. Furthermore, sleep difficulties are common in childhood, particularly in neurodevelopmental disorders characterised by language learning impairments (e.g., autism spectrum disorder; ASD), but little progress has been made in examining whether learning and sleep difficulties are related in these groups. Comparisons across ages, as well as between typical and atypical groups of the same age, offer an opportunity to test theories of consolidation in terms of whether they can explain the substantial variability across and within development.

This project is divided into two key strands to provide a comprehensive evaluation of the influence of sleep on consolidation of memory in development. Strand 1 focuses on typical development, using children aged 10-12 (when slow-oscillation activity peaks), as well as adults, and in some cases younger children. Strand 2 focuses on atypical development, comprising the first systematic evaluation of whether atypical sleep relates to language learning difficulties in children with ASD with varying language phenotypes and in children with language impairment (LI) without ASD. This enables us to separate learning mechanisms associated with ASD from those attributable to language impairment.

Our experiments involve learning of new materials, followed by a delay. For sleep conditions, participants' brain activity is recorded at home. Later tests determine the strength and nature of the new memory. For example, one study addresses whether sleep facilitates stabilisation of new memories, and looks at the optimal delay between learning and sleep (which may be particularly pertinent for children). Another examines the influence of prior knowledge on consolidation during sleep. Adults and children differ in terms of the prior knowledge that they bring to a learning situation and it is possible that this can mask the stronger consolidation ability of children. Furthermore, children with language impairments have impoverished vocabularies which may lead to a 'Matthew Effect' (i.e., the rich get richer and the poor get poorer) in the consolidation of new words; our studies will test this hypothesis directly.

Many studies focus on the role of sleep in language learning. We track the timecourse of learning spoken words and their meanings, and the extent to which this new information is strengthened over time, integrated with existing knowledge, and generalised to new exemplars. Such studies permit a thorough examination of whether language learning difficulties are associated with differences in sleep architecture in ASD and LI. We will exploit data collected from the same children over a 2-year period to examine whether sleep variables predict vocabulary outcomes over a longer period.

Finally, in a cross-cutting study we examine the generality of any effects of sleep across both typical and atypical development by examining the influence of sleep in a rather different type of memory that is nonetheless dependent on consolidation: spatial location.

We aim to create a comprehensive theory of typical and atypical consolidation and forgetting across wake and sleep, and advance theories of typical language acquisition and language heterogeneity in ASD and LI. The theoretical applications of the planned research have the potential to improve our practical understanding of how to make memories stick in children and adults, and ultimately improve outcomes.

 

Engineering sleep for memory consolidation in adolescence: A sleep extension study (PI: Dr Lisa Henderson, Funder: Waterloo Foundation)

Insufficient sleep is detrimental to daytime functioning, with adverse effects observed across attention, mood, and behaviour. Research also consistently demonstrates that sleep (particularly ‘slow-wave’ sleep i.e., 0.4-5Hz delta activity) works to actively consolidate newly learned material, strengthening it and leaving it more resistant to interference. At least half of UK adolescents are argued to be chronically sleep deprived, receiving substantially less than the recommended 9 hours per night. Tackling this issue is of prime importance. A previous study suggested that simply extending children’s sleep by just one hour leads to substantial benefits for cognitive and neuropsychological function. However, we do not know precisely how sleep extension alters the nature of the sleep cycle or whether it benefits consolidation of newly learned material for long-term use. In addressing these questions we aim to clarify the neurophysiological and educational value of sleep extension in adolescence. Sixty adolescents (13-15 years) will be randomly allocated to a control (sleep as usual) or sleep extension (bedtime brought forward by 20 minutes per night over a five day period) group. As well as assessing effects of sleep extension on mood and daily cognition (i.e., attention, working memory), we will establish whether there are benefits to memory consolidation (e.g., memory for newly learned words). Following a baseline and extension/control period, sleep architecture will be recorded in children’s usual environments via home sleep electroencephalography (EEG), allowing us to examine whether any improvements in memory consolidation following sleep extension are associated with key markers of sleep consolidation (e.g. slow-wave activity). This research has clear societal impact for health and education as well as for advancing our theoretical understanding of sleep-associated memory consolidation during adolescence.