Comments
・I thought this was a perspective that would significantly change the conventional view ofchild development. It can be said that conventional developmental theories have basicallyexamined mechanisms based on the assumption that children are awake and active. It is anextremely important perspective to consider how the seemingly restful hours of sleep affectdevelopment. In particular, given that approximately one-third of the day is spent sleeping, it
made me think that it is necessary to approach development from the perspective of bothwaking activities and sleeping/resting time.
・It made me think again about the many different types of sleep. It was also very interesting
to discuss that the mechanism also differs depending on age and developmental characteristics.
I thought that the method of closely following what kind of sleep appears at what time of day
and to what extent is important as a research method, and I thought it would be very helpful.
・This finding seemed a bit dangerous if used incorrectly. I fear that if sleep is reported tohave a positive or negative impact on development, the will (desire) to control into
uncontrolled areas may become stronger. Without attention, this information makes parents
anxious and to think "Don't let children have this kind of sleep!".
・The question is whether the effects of sleep can be viewed as a sleep stand-alone process.
There are issues of the environment in the home, such as whether parents sleep together or
how much storybooks are read to them before bed, or the environment where they live, suchas the noise outside when they are sleeping. Of course, this presentation also suggests a
relationship between socioeconomic variables and sleep. However, I think it is important tohave a perspective on the process leading up to sleep that goes beyond the indicators thatappear in numerical values.
・In clinical practice, it is recognized that child development and sleep are quite related. In
particular, children with developmental disorders do not sleep well. It is said that their brain
structure does not allow for good brain switching to get a good night's sleep. Sleep hygiene
instruction can lead to better switching, which can decrease the tendency for hyperactivity if
the child has ADHD.
・I have read a paper on how facial expression recognition in ADHD is related to sleep. The
results showed that when the effects of sleep were controlled for, there was no difference infacial expression recognition, but when the experiment was conducted under sleep deprived

conditions, it affected facial expression recognition in ADHD. I wondered if not controllingfor differences in sleep would lead to erroneous interpretations.
・Some people do not sleep much during the week and sleep a lot on weekends, which candisrupt the rhythm of sleep. This also affects various activities.
QuestionsThank you so much for these highly valuable and interest comments and reflections! Pleasefind my responses to the specific questions below.
・The perspective of the connection between sleep and language development was new to me.
Why did you decide to make that connection?

Thank you so much for this question! My PhD and postdoctoral research was primarily
focused on understanding mechanisms of language learning – how do we lay down newmemories for new words and how can we use this understanding to optimize language
learning over the lifespan? We took a domain general approach to addressing these questions,taking the stance that language learning draws on general cognitive learning systems.
Simultaneously, there was growing interest in the view that sleep plays an active role inconsolidating newly formed memories, transferring them to long term memory stores. We
thus began investigating whether the same is true for memories of newly learned language
and indeed we observed the same effects in adults at first. Of course, we know that sleepchanges radically over development, so I then became fascinated with understanding how
these changes in sleep architecture might support language development. We also know thatsleep is often disrupted in children with neurodevelopmental disorders where language
development is often hampered.
・I am a literacy researcher, but I have never thought of relationship between sleep and literacy.
Besides language development, are there any other studies on literacy as affected by sleep?

Yes! There are studies (carried out by my group and numerous others) that have examinedthe effects of sleep on orthographic word learning, revealing similar sleep benefits (i.e., newwritten words are recalled better if a period of sleep follows learning relative to a period ofwake in both children and adults, see here for a recent review). There are also studies thathave shown that the critical language skills that underpin literacy (i.e., the fine tuning of

phonological representations) are also sleep-dependent. Thus, taking a domain generalapproach to language and literacy, and the assumption that general cognitive memory
mechanisms underpin these aspects of development, there’s good reason to assume thatliteracy development would be influenced by sleep in similar ways to vocabulary development.
・Japanese children sleep very little and stay up late at night. In the UK, I think children go
to bed earlier. I think there are cultural differences in what time of day they go to bed. Do you
have any thoughts on such cultural differences?

This is an interesting and important question. There are certainly cultural differences insleeping habits and sleep hygiene. Whilst there is some research that aims to characterizethese fascinating differences, there’s much to be done to understand the impact that suchdifferences have on different aspects of development, including language development. Onerelevant and important area where research has been carried out is the impact of the timingof the school day on sleep and the influence of this on key aspects of development (including
performance at school, but also daily cognition and mood), with this being one example of
how cultural differences might influence development.
・What are your thoughts on continuity from fetal life? The language area on brain is quite
well formed at birth. I think that "children who get enough sleep" are "children with a welldeveloped language area". Is the influence of language area maturation a controlled study
design?

Thank you for raising this important point. So, as I hinted at in the presentation, it could justbe that individuals who sleep well are also individuals who have more mature brain
development, globally speaking. This may at least partly account for the associations that wesee. However, environmental influences on sleep (e.g., tech use at bedtime, poor diet, noise
pollution, over-crowding) still have an impact on sleep, and intervention studies show that
improving these aspects can have positive effects on cognitive and social skills as well as healthand wellbeing. Thus, it’s not the case that the sleep of sleep on development is fixed from thefetal stage and amenable to change.
・ASD and TD differed in sleep; do these differences in language learning between ASD and
TD control for sleep quality?

Another important point! It is the case that children with ASD wake up more frequently andsleep for shorter durations, as well as spending less time in non-rapid eye movement (NREM)
sleep. These differences in sleep quality may well go some way to accounting for thedifferences in sleep architecture that we observed (e.g., lower proportion of slow waves andsleep spindles).
・I think that the amount of sufficient sleep varies from person to person. Can such individual
differences be measured? Also, was such an individual difference taken into account in yourstudies?

I completely agree with this assumption. The amount of sleep varies across and within
individuals. Our studies (both in the lab and in the longitudinal cohort datasets) aim tounderstand how these individual differences relate to different aspects of development.
・I have heard that narcolepsy is genetically difficult for people to cure. Is sleep a matter ofhabit or physical constitution?

This is another really interesting and important question! Research tells us that whilst sleep
is strongly genetically influenced it also has a strong environmental contribution, and hence
it IS amenable to improvement, despite myths.