Sleep, Language Acquisition and Development

 

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, Co-Is: Prof Gareth Gaskell and Dr Fay Fletcher, 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.