Print version ISSN 0004-282X
Arq. Neuro-Psiquiatr. vol.62 no.2a São Paulo June 2004
Cognitive dysfunction in children with sleep disorders
Disfunção cognitiva em crianças com distúrbios do sono
Luciane Bizari Coin de CarvalhoI; Lucila Bizari Fernandes do PradoII; Luciana SilvaIII; Marilaine Medeiros de AlmeidaIII; Tatiana Almeida e SilvaIII; Célia Maria Alcântara Machado VieiraIII; Álvaro Nagib AtallahIV; Gilmar Fernandes do PradoV
Sleep Disorders Center, Departments of Neurology and Emergency Medicine, Federal University of São Paulo São Paulo SP, Brazil (UNIFESP)
IPhD, Department of Neurology, Sleep Disorders Center, UNIFESP
IIMD, Department of Neurology, Sleep Disorders Center, UNIFESP
IIIDepartment of Neurology, Sleep Disorders Center UNIFESP
IVMD, PhD, Brazilian Cochrane Center
VMD, PhD, Departments of Neurology and Emergency Medicine, Sleep Disorders Center, UNIFESP
Sleep is basic for physical and cognitive development and some studies have suggested that there may be an association between sleep disorders (SD) and cognitive dysfunction (CD) in children. Little is known, however, about SD and cognition in 7-10-year-old children, a fact that motivated the present study.
METHOD: We applied an SD questionnaire in 1180 children, 547 with SD and 633 without SD (CG), to assess cognition with a screening test (Bender Visual Motor Gestalt Test - BT).
RESULTS: We observed a similar frequency of CD in the children with SD (39%) and that ot the CG (40%). The 8-year-old children with SD presented a lower prevalence of CD than the CG (SD=6%, n=6; CG=13%, n=16; p=0.04).
CONCLUSION: The frequency of children with CD was equal in the study and control groups when considering the total sample (7- to 10-year-old children). In contrast to our expectations, the SD group of 8-year-old children presented a lower frequency of CD than the control group.
Key words: sleep disorders, children and cognitive dysfunction.
O sono é fundamental no desenvolvimento físico e cognitivo, vários estudos na literatura sugerem haver associação entre distúrbio do sono (DS) e disfunões cognitivas (DC) em crianças. Pouco se sabe, no entanto, sobre DS e cognição na faixa etária de 7 a 10 anos, motivo porque empreendemos este estudo.
MÉTODO: Aplicamos um questionário de DS em 1180 crianças: 547 com DS e 633 sem DS (GC), avaliandose cognição pelo Teste Gestáltico de Bender (TB).
RESULTADOS: Observamos proporção semelhante de DC nas crianças com DS (39%) e nas do GC (40%). As crianças de 8 anos do DS apresentaram menor prevalência de DC do que as do GC (DS=6%, n=6; GC=13%, n=16; p=0,04).
CONCLUSÃO: A proporção de crianças com DC foi igual nos grupos estudo e controle quando consideramos a amostra total (crianças de 7 a 10 anos). Contrariando nossas expectativas, o grupo DS de 8 anos apresentou menos DC que o grupo controle.
Palavras-chave: distúrbios do sono, crianças e disfunção cognitiva.
Sleep is basic for the physical and cognitive development of children1, but studies about sleep disorders (SD) and their consequences in this age group are few and inconclusive. About 35 to 46% of schoolage children and 20 to 25% of adolescents present some kind of SD. Twenty percent of schoolage children snore, suffer from daily fatigue and experience difficulty to sleep at least once a week, and 14% of them have a poor quality of sleep2. Attempts have been recently made to show a relation between SD and learning problems3 in children that present a poor quality of sleep, irregular bedtime schedules and fatigue during classes. Children without difficulties in waking up in the morning are more motivated during classes whereas children with sleep restriction present difficulty in abstract thinking and verbal creativity4. Children with fragmented sleep had lower perfomance in neurobehavioral tests5, those with lower sleep efficiency had a higher percentage of incorrect responses in working memory tasks6, and those with acute sleep restriction increased innatentive behaviors7.
Sleep breathing disorders are highly prevalent among children and have been suggested to reduce cognitive performance more intensely than other SD, affecting memory, attention and visuoconstructive ability8-10. Academic performance has been investigated in Brazil11, but little information exists about SD and cognitive dysfunction in Brazilian 7-to 10-yearold children12-13 and the few studies available involved inadequate samples, mainly because of the difficulty to study large samples in view of the fact that most tests for the assessment of cognitive function are difficult to apply.
On this basis, we undertook the present study evaluating the performance of SD children comparing with nonsleep disorder children by using a screening test for cognition.
We studied 1180 children, 7-to 10 year-old, from August 1999 to June 2000, proceeding from 9 State Schools of Basic Education of the Region Center-South of the São Paulo City, Brazil. These schools had been drafted, among 35 possible ones, for representing each quarter of this region of which the university is a part. The study protocol (447/00) was approved by the institutional review board of the Federal University of Sao Paulo, UNIFESP. The Consent was signed by the responsible Director of Education, the principals of the schools and the parents of the children.
About 5400 Questionnaires of Alterations of Sleep in Infancy (QASI), adapted for the Portuguese of Brazil, from Bruni et al.14 had been delivered. Until June 2000, 3612 questionnaires answered by the parents of the children had been returned and 589 were excluded because of incorrect filling in. For definitions of habits related to the normal sleep and SD, 3023 questionnaires were analyzed15. Six hundred and forty children presented witSD in the QASI14 and, they were all included for cognitive evaluation. We also elected randomically 640 normal children from a total of 2383 as a control group (CG). We adopted a stratified procedure for randomization to pair for gender and age. A team of 12 trained psychologists had gone back to the schools and had assessed cognition with the screening test (Bender Visual Motor Gestalt Test - BT16-18), in 547 SD children and 633 CG group. The BT is aproppriated to screen cognition deficit because it can be rapidly applied (10 minutes) and has easy to understand instructions16-18. Fifty and three children of the group with SD and 7 children of the CG had not been tested because of absence during the days where the application proceeded by BT. The searching psychologist analyzed the BT and was unaware of which group the child belonged to: SD or CG. The SD group consisted of children with sleep breathing disorders (SBD), disorders of arousal (DA), difficulty in initiating and maintaining sleep (DIMS), disorders of sleepwake transition (DSWT), and daytime sleepiness (DSS). Children taking medicines, presenting psychiatric disorders (psychosis, autism) or genetic syndromes were not assessed. The diagnosis of cognitive dysfunction (CD) was analyzed according to the BT criterias16-18.
Statistical analyses: the data were analyzed in relation to the CG, i.e., by determining if the ratio of children with CD in the SD group differed from that observed in the CG. We used the chisquare and Fisher tests, with the level of significance set at p<0.05. The explanation variables were: gender, age (7-, 8-, 9- and 10-yo), total sleep time (< 8h and > 8h) and start time school (morning, afternoon).
The demographic data of this study population are shown in Tables 1 and 2. The SD group consisted of 79 children (14%) with sleep breathing disorders, 454 children (83%) with disorder of arousal, 16 children (3%) with difficulty in initiating and maintaining of sleep 84 children (15%) with disorder of the sleep-wake transition, and 61 children (11%) with daytime sleepiness. There was no association among these sleep disorders and cognitive dysfunction (Tables 3 and 4). The grade and age variables were highly correlated and therefore were analyzed as single variable (Pearson Correlation = 0.946; p=0.01).
The gender distribution of children with CD did not differ between the SD group and CG: 122 (48%) were boys (Table 1). The age distribution of the children with CD in the SD group (n=212) and in CG (n=252) is shown in Table 2.
Fourteen SD children and 9 CG children did not report how much time they slept; of the 533 SD children and 624 CG children that provided this information, 491 (92%) and 578 (93%) children, respectively, slept more than 8 hours, and only 42 SD children and 46 CG children slept less than 8 hours, with no significant difference in the prevalence of CD between the two groups (41% and 37%, respectively).
Among the start time school-afternoon (STS-A) children, 246 (45%) were from the SD group and 301 (48%) from the CG. Of the start time school-morning (STS-M) children, 301 (55%) were from the SD group and 332 (52%) from the CG. The prevalence of CD did not differ significantly between these groups (40% and 38% respectively). Among the 8-year-old children with SD from STS-A, CD was more prevalent for the CG (CG=13%, n=16; SD=6%, n=6; p=0.04; OR=0.31; 95%CI=0.1 to 0.9).
The children sleep questionnaires answered by the parents are criticized for their imprecision because the parents cannot always know what happens to the children, mainly if they sleep in another room and do not make noise or call their parents19-20. Besides, some adults do not perceive the sleep of their child as a "problem" and believe that sleep disorders are part of normal child development.
The questions about learning and cognitive skills depend on factors beyond those associated with SD, with an important influence of low income, children's work, lack of disease treatment, family disharmony, psychological problems and others, in addition to school difficulties. The complaints directly related to the mothers, such as the inability to impose limits to the children, anger roused by the children's demands and uncertainty about their mothering ability, produce anguish and anxiety in the child, which may manifest as sleep disorders20.
Paradoxically, in this study we observed a higher frequency of CD among 8-year-old CG children from STS-A. We could not find an explanation for the better BT performance of SD children; the fact that the child wakes up many times at night or has a poor quality of sleep may indirectly stimulate other neural pathways that can be used in cognitive functions, giving an impression of learning when there is only training or an adaptation to determined functions21-23. Phenomena such as the excessive number of arousals, anxiety, concern with experiences and a search for external references1 can be associated with functional activities predominantly depending on the right cerebral hemisphere, indirectly promoting a training for functions detected in the BT, masking the cognitive deficiency dependent on visuo-motor functions.
Literature studies on 7-to 10-year-old children suggest that these children present equal physical and psychological characteristics but, in some studies, the 8- year-old children presented different behaviors sometimes even opposite to the pattern of expected for this age24-26. In our study, 7- to 8-year-old children differed amongst themselves and in relation to the other ages, and 9- to 10-year-old children showed a similar pattern of sleep and cognition.
It has also been shown that 8-year-old children present increased slow wave sleep, increased REM27 and many nightmares28, findings that have not yet been been associated with any specific etiology, and that do not reveal associated physical or psychological disorders, although the excessive number of arousals causes irregular secretion of growth hormone29.
With respect to cognitive development, we know that 8-year-old children differ from younger ones by being in the concrete operation period, i.e., they use egocentrism to understand relations and symbols, taking into account all the aspects of a situation, putting themselves in the place of others, perceiving the logic of the facts, but without the capacity to abstract ideas, which will only appear at about 12 years of age. They can, for example, perceive that dreams are inside their head and not actually present in the room; they know that dreams are unreal, but do not understand what they are, what they do and how they arrived there; they dominate the language and use it in the formation of groups, comparing themselves with their friends in terms of creativity and productivity. Sexuality is in the latency phase, although the children talk much about it and use it in their games as a determinant factor in the formation of rival groups1.
These physical, cognitive, psychological, and adaptive characteristics of 8-year-old children indicate that these children are passing through a phase of many changes and with special patterns specific for this age. Further separate investigation of this age is needed for a better understanding of the causes and consequences of this differentiation. As a whole, from 7- to 10-year-old children do not present cognitive dysfunction associated with sleep disorders.
Acknowledgements - Mrs Elletra Greene for the review translation and the Psychologist team: KV Serrano, AQM Alves, PHM Carneiro, MV Chucre, WH Oliveira, MI Bonavito, EL Mat e VC Ronque.
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Received 1 April 2003, received in final form 17 September 2003.
Accepted 4 November 2003.
Supported by FAPESP 00/075133.
Dr. Gilmar Fernandes do Prado - Rua Claudio Rossi 394 - 01547-000 São Paulo - SP - Brazil. E-mail: email@example.com