A cross-syndrome study of the differential effects of sleep on declarative memory consolidation in children with neurodevelopmental disorders.

Sleep plays an active role in memory consolidation. Because children with Down syndrome (DS) and Williams syndrome (WS) experience significant problems with sleep and also with learning, we predicted that sleep-dependent memory consolidation would be impaired in these children when compared to typically developing (TD) children. This is the first study to provide a cross-syndrome comparison of sleep-dependent learning in school-aged children. Children with DS (n = 20) and WS (n = 22) and TD children (n = 33) were trained on the novel Animal Names task where they were taught pseudo-words as the personal names of ten farm and domestic animals, e.g. Basco the cat, with the aid of animal picture flashcards. They were retested following counterbalanced retention intervals of wake and sleep. Overall, TD children remembered significantly more words than both the DS and WS groups. In addition, their performance improved following night-time sleep, whereas performance over the wake retention interval remained stable, indicating an active role of sleep for memory consolidation. Task performance of children with DS did not significantly change following wake or sleep periods. However, children with DS who were initially trained in the morning continued to improve on the task at the following retests, so that performance on the final test was greater for children who had initially trained in the morning than those who trained in the evening. Children with WS improved on the task between training and the first retest, regardless of whether sleep or wake occurred during the retention interval. This suggests time-dependent rather than sleep-dependent learning in children with WS, or tiredness at the end of the first session and better performance once refreshed at the start of the second session, irrespective of the time of day. Contrary to expectations, sleep-dependent learning was not related to baseline level of performance. The findings have significant implications for educational strategies, and suggest that children with DS should be taught more important or difficult information in the morning when they are better able to learn, whilst children with WS should be allowed a time delay between learning phases to allow for time-dependent memory consolidation, and frequent breaks from learning so that they are refreshed and able to perform at their best.

The Importance of Sleep: Attentional Problems in School-Aged Children With Down Syndrome and Williams Syndrome.

In typically developing (TD) children, sleep problems have been associated with day-time attentional difficulties. Children with developmental disabilities often suffer with sleep and attention problems, yet their relationship is poorly understood. The present study investigated this association in school-aged children with Down syndrome (DS) and Williams syndrome (WS). Actigraphy and pulse oximetry assessed sleep and sleep-disordered breathing respectively, and attention was tested using a novel visual Continuous Performance Task (CPT).Attentional deficits were evident in both disorder groups. In the TD group, higher scores on the CPT were related to better sleep quality, higher oxyhemoglobin saturation (SpO2), and fewer desaturation events. Sleep quality, duration, and SpO2 variables were not related to CPT performance for children with DS and WS.

Sleep enhances memory consolidation in children.

Sleep is an active state that plays an important role in the consolidation of memory. It has been found to enhance explicit memories in both adults and children. However, in contrast to adults, children do not always show a sleep-related improvement in implicit learning. The majority of research on sleep-dependent memory consolidation focuses on adults; hence, the current study examined sleep-related effects on two tasks in children. Thirty-three typically developing children aged 6-12 years took part in the study. Actigraphy was used to monitor sleep. Sleep-dependent memory consolidation was assessed using a novel non-word learning task and the Tower of Hanoi cognitive puzzle, which involves discovering an underlying rule to aid completion. Children were trained on the two tasks and retested following approximately equal retention intervals of both wake and sleep. After sleep, children showed significant improvements in performance of 14% on the non-word learning task and 25% on the Tower of Hanoi task, but no significant change in score following the wake retention interval. Improved performance on the Tower of Hanoi may have been due to children consolidating explicit aspects of the task, for example rule-learning or memory of previous sequences; thus, we propose that sleep is necessary for consolidation of explicit memory in children. Sleep quality and duration were not related to children's task performance. If such experimental sleep-related learning enhancement is generalizable to everyday life, then it is clear that sleep plays a vital role in children's educational attainment.

Cross syndrome comparison of sleep problems in children with Down syndrome and Williams syndrome.

Based on previous findings of frequent sleep problems in children with Down syndrome (DS) and Williams syndrome (WS), the present study aimed to expand our knowledge by using parent report and actigraphy to define sleep problems more precisely in these groups. Twenty-two school-aged children with DS, 24 with WS and 52 typically developing (TD) children took part in the study. Each child wore an actiwatch for a minimum of four nights and parents completed the Children's Sleep Habits Questionnaire (CSHQ). Sleep problems were common in both developmental disorders. Children with DS had the greatest sleep disruption, with frequent and longer night wakings as well as restlessness. Parents reported symptoms of sleep-disordered breathing and a range of other problems including grinding teeth, bedtime resistance and sleep anxiety. Children with WS had problems initiating sleep and parents also reported bed-wetting and body pain. Despite these problems, the mean actual sleep time, as measured by actigraphy, did not differ between the three groups. CSHQ reports were in agreement with actigraphy for children's sleep duration, but this was not the case for sleep latency, restlessness and the night wakings variables. Sleep problems in DS and WS are common and appear to be syndrome-specific. Due to the inaccuracy of parent report, it is recommended that children at risk undergo objective measures of sleep assessment.

Characterisation of sleep problems in children with Williams syndrome.

Sleep is critical to optimal daytime functioning, learning and general health. In children with established developmental disorders sleep difficulties may compound existing learning difficulties. The purpose of the present study was to evaluate the prevalence and syndrome specificity of sleep problems in Williams syndrome (WS), a neurodevelopmental disorder affecting around 1 in 20,000 live births. Parents of 64 children with WS, aged 6-12 years, and 92 age matched healthy controls were surveyed about their child's sleep habits. The Child Sleep Habits Questionnaire, general health and background information were collected from the parents. Ninety seven percent of parents reported that their children had sleep problems and reported a high prevalence of sleep difficulties: greater bedtime resistance, sleep anxiety, night waking and daytime sleepiness. This is the first study to our knowledge to survey sleep problems in a large cohort of school age children with WS. Sleep problems in children with learning difficulties are often amendable to treatment if diagnosed early. Furthermore the negative impact of sleep disturbances on daytime behaviour and learning should be measured before diagnoses of behaviourally defined disorders are considered.