Prelims.qxd 1/25/05 3:03 AM Page ii PRINCIPLES AND PRACTICE OF PEDIATRIC SLEEP MEDICINE ISBN 0–7216–9458–6 Copyright © 2005 by Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher. Notice Medicine is an ever-changing field. Standard safety precautions must be followed, but as new research and clinical experience broaden our knowledge, changes in treatment and drug therapy may become nec- essary or appropriate. Readers are advised to check the most current product information provided by the manufacturer of each drug to be administered to verify the recommended dose, the method and dura- tion of administration, and contraindications. It is the responsibility of the treating physician, relying on experience and knowledge of the patient, to determine dosages and the best treatment for each individ- ual patient. Neither the Publisher nor the editor assumes any liability for any injury and/or damage to persons or property arising from this publication. The Publisher Library of Congress Cataloging-in-Publication Data Principles and practice of pediatric sleep medicine/Stephen H. Sheldon...[et al.].– 1st ed. p. cm. Includes bibliographical references. ISBN 0-7216-9458-6 1. Sleep disorders in children. 2. Children–Sleep. I. Sheldon, Stephen H. RJ506.S55P746 2005 618.92′8498–dc22 2004066249 Acquisitions Editor: Dolores Meloni Project Manager: Joan Nikelsky Design Coordinator: Ellen Zanolle Printed in the United States of America. Last digit is the print number: 9 8 7 6 5 4 3 2 1 Prelims.qxd 1/25/05 3:03 AM Page iii We dedicate this book, first to our families and, second, to all of the children and their families who have hadthe courage to work with us and help us achieve a better understanding of how to recognize and treat sleep problems in the child. Prelims.qxd 1/25/05 3:03 AM Page v Contributors Roberto L. Barretto, MD Center; Medical Director, The Methodist Hospital Clinical Assistant Professor, Department of Sleep Disorders Center, Houston, Texas Otolaryngology—Head and Neck Surgery, Sleep in Neurologic Disorders University of California, Irvine, School of Medicine, Irvine; Attending Pediatric David Gozal, MD Otolaryngologist, Children’s Hospital of Orange Children’s Foundation Chair of Pediatric Research County, Orange, California and Professor of Pediatrics, Pharmacology and Otolaryngologic Management of Sleep-Related Breathing Toxicology, and Psychology and Brain Science, Disorders University of Louisville School of Medicine; Director, Comprehensive Sleep Medicine and Lee J. Brooks, MD Apnea Center, Kosair Children’s Hospital; Vice Clinical Associate Professor of Pediatrics, Chairman for Research and Director, Kosair University of Pennsylvania School of Medicine; Children’s Hospital Research Institute, Louisville, Attending Physician, Pulmonary Division, The Kentucky Children’s Hospital of Philadelphia, Philadelphia, Consequences of Obstructive Sleep Apnea Syndrome Pennsylvania Obstructive Sleep Apnea Syndrome in Infants and Children: John H. Herman, PhD, FCCP, Dipl ABSM Clinical Features and Pathophysiology; Enuresis in Professor of Psychiatry and Director, Sleep Children with Sleep Apnea Medicine Fellowship Program, UTSouthwestern Medical Center School of Medicine; Director, Ronald D. Chervin, MD, MS Sleep Disorders Center for Children, Children’s Associate Professor of Neurology, University of Medical Center of Dallas, Dallas, Texas Michigan Medical School; Director, Sleep Chronobiology of Sleep in Children; Circadian Rhythm Disorders Center/Michael S. Aldrich Sleep Disorders: Diagnosis and Treatment; Pharmacology of Disorders Laboratory, Department of Neurology, Sleep Disorders in Children University Hospital, Ann Arbor, Michigan Attention Deficit, Hyperactivity, and Sleep Disorders Eliot S. Katz, MD Instructor, Harvard Medical School; Attending, Richard Ferber, MD Division of Respiratory Diseases, Children’s Associate Professor of Neurology, Harvard Hospital Boston, Boston, Massachusetts Medical School; Director, Center for Pediatric Diagnosis of Obstructive Sleep Apnea Syndrome in Infants Sleep Disorders, Children’s Hospital Boston, and Children Boston, Massachusetts Michael Kohrman, MD Mark E. Gerber, MD, FACS, FAAP Associate Professor of Pediatrics and Neurology, Assistant Professor, Department of University of Chicago Pritzker School of Otolaryngology—Head and Neck Surgery, Medicine; Director, Pediatric Clinical Northwestern University Feinberg School of Neurophysiology, University of Chicago Medicine, Chicago; Attending, Children’s Children’s Hospital, Chicago, Illinois Memorial Hospital, Chicago, and Evanston Idiopathic Hypersomnia Northwestern Healthcare (Evanston, Glenbrook, and Highland Park Hospitals), Evanston, Illinois Suresh Kotagal, MD Otolaryngologic Management of Sleep-Related Breathing Disorders Professor and Chair, Division of Child and Adolescent Neurology, Department of Neurology, Daniel G. Glaze, MD Mayo Medical School; Consultant, Sleep Disorders Center, Mayo Clinic, Rochester, Associate Professor of Pediatrics and Neurology, Minnesota Baylor College of Medicine; Medical Director, The Texas Children’s Hospital, the Children’s Sleep Narcolepsy in Childhood v Prelims.qxd 1/25/05 3:03 AM Page vi vi Contributors Meir H. Kryger, MD, FRCPC Gerald M. Rosen, MD, MPH Professor of Medicine, University of Manitoba Associate Professor, Department of Pediatrics, Faculty of Medicine; Director, Sleep Disorders University of Minnesota School of Medicine; Centre, St. Boniface Hospital Research Center, St. Medical Director, Pediatric Sleep Center, Boniface General Hospital, Winnipeg, Manitoba, Children’s Hospitals and Clinics, St. Paul, Canada Minnesota; Pediatric Sleep Specialist, Minnesota Differential Diagnosis of Pediatric Sleep Disorders Regional Sleep Disorders Center, Hennepin County Medical Center, Minneapolis, Minnesota Mark W. Mahowald, MD Case-Based Analysis of Sleep Problems in Children; Disorders of Arousal in Children Professor of Neurology, University of Minnesota School of Medicine; Director, Minnesota Regional Sleep Disorders Center, Department of Neurology, Stephen H. Sheldon, DO, FAAP Hennepin County Medical Center, Minneapolis, Associate Professor of Pediatrics, Northwestern Minnesota University, Feinberg School of Medicine; Disorders of Arousal in Children Director,Sleep Medicine Center, Children’s Memorial Hospital, Chicago, Illinois Carole L. Marcus, MBBCh Introduction to Pediatric Sleep Medicine; Anatomy of Sleep;Polysomnography in Infants and Children; Professor of Pediatrics, University of Pennsylvania Physiologic Variations during Sleep in Children; School of Medicine; Director, Pediatric Sleep Disordersof Initiating and Maintaining Sleep; Post- Center, The Children’s Hospital of Philadelphia, Traumatic Hypersomnia; Kleine-Levin Syndrome and Philadelphia, Pennsylvania Recurrent Hypersomnias; Sleep in Neurologic Diagnosis of Obstructive Sleep Apnea Syndrome in Infants Disorders;The Parasomnias; Sleep-Related Enuresis; and Children; Treatment of Obstructive Sleep Apnea Pharmacology of Sleep Disorders in Children Syndrome inChildren Julie L. Wei, MD Susanna A. McColley, MD Assistant Professor, Department of Associate Professor of Pediatrics, Department of Otolaryngology—Head and Neck Surgery, Pediatrics, Northwestern University Feinberg University of Kansas School of Medicine, Kansas School of Medicine; Division Head, Pulmonary City, Kansas; Attending Physician, Pediatric Medicine, Children’s Memorial Hospital, Chicago, Otolaryngology, Children’s Mercy Hospital, Illinois Kansas City, Missouri Primary Snoring in Children Otolaryngologic Management of Sleep-Related Breathing Disorders Louise Margaret O’Brien, PhD Research Fellow, Department of Pediatrics, Marc Weissbluth, MD University of Louisville School of Medicine, Professor of Clinical Pediatrics, Northwestern Louisville, Kentucky University Feinberg School of Medicine; Active Consequences of Obstructive Sleep Apnea Syndrome Attending, Children’s Memorial Hospital, Chicago, Illinois Judith Owens, MD, MPH Sleep and Colic Associate Professor of Pediatrics, Division of Ambulatory Pediatrics, Brown Medical School; Director, Pediatric Sleep Disorders Clinic, Hasbro Children’s Hospital, Providence, Rhode Island Epidemiology of Sleep Disorders during Childhood Prelims.qxd 1/25/05 3:03 AM Page vii Preface Sleep medicine is a unique medical discipline, 1. Primary sleep-related pathology may directly the one area of specialization that focuses on cause daytime symptoms, and only through patients’ health and disease during the hours of treatment of the sleep disorder is resolution sleep. Pediatric sleep medicine holds special sig- possible. nificance in that it is concerned with about half 2. Sleep-related pathology may be a co-morbid of the child’s life during the important early condition contributing to daytime symptoma- years of development. Because sleep constitutes tology, and through treatment of the sleep- such a large proportion of the child’s day, and related pathology, the patient becomes more because the development of the neurologic responsive to treatment of the co-existing dis- structures responsible for sleep, in patterns of orders. increasing complexity and predictability, occurs 3. A child’s sleep difficulties may have greater so rapidly during the early months and years of impact on other family members than on the life, the maturation of these systems is clearly affected child, causing a caretaker, for exam- among the most important of neurodevelopmen- ple, to be sleep deprived, with medical and tal milestones to be met. Early disruption of emotional compromises (including impaired these vital processes has major cognitive and ability to care for the child). Treating these possibly emotional consequences that are only problems can improve the lives of child and recently becoming clear. Studies have repeatedly family members alike. confirmed the importance of sleep for the acqui- As we continue to gain better understanding of sition of new knowledge and for processing and the effect of sleep disorders on children, major maintaining information previously gained. advances will be made, with great significance Knowledge of primary and secondary sleep- for all three of these scenarios, including insight related disorders also has been shown to be into the often unclear area of cause and effect— essential to the understanding of many other namely, whether disordered sleep is a cause or a childhood disorders and in the development of result of a specific disease or disorder. proper treatment. Sleep disorders in infants and children reflect Principles and Practice of Sleep Medicine in the an interplay among many factors, including Child, first published as a separate volume from central nervous system function, parental-child Principles and Practice of Sleep Medicine(2nd edi- interaction, social stress, patient needs, and tion) in 1995, helped move the practice of pedi- other medical conditions. Comprehensive atric sleep medicine from the sphere of adult knowledge of these interactions is essential for medicine to one that is overseen by professionals all child-care professionals who want to deliver who have dedicated their careers to the health optimal management. This book provides and well-being of the pediatric patient. As stated resources for sleep medicine specialists as well as in the Preface to that volume, “In recent years, a primary care practitioners to use to deliver the robust scientifically based body of knowledge best possible care to their pediatric patients has emerged, and the tools to diagnose and effec- throughout the 24-hour day. tively treat children with sleep disorders are now available.” Principles and Practice of Pediatric Stephen H. Sheldon, Chicago Sleep Medicine represents another step in the development of pediatric sleep medicine as a dis- Richard Ferber, Boston tinct discipline. Meir Kryger, Winnipeg Diagnosis and management of sleep disorders in children may hold unique significance in at least three very important ways: vii Prelims.qxd 1/25/05 3:03 AM Page ix Acknowledgments The editors wish to thank the entire editorial staff foresight to understand the importance of sleep in at Saunders/Elsevier for their outstanding efforts health and disease in the pediatric patient. in the creation of this book. Specifically, we wish Beginning with the scientific foundation laid by to single out Joan Nikelsky and Delores Meloni pioneers Nathaniel Kleitman, Arthur Parmelee, for their patience and persistence, without which Jr., and Heinz F.R. Prechtl, many other child this project could have never been completed. health care practitioners have begun to follow in We also would like to thank all of the coura- their footsteps, delving into the life of children at geous health care professionals who care for chil- night. These researchers and practitioners of pedi- dren during sleep—for their dedication and atric sleep medicine truly are leading the way. ix Ch01.qxd 1/25/05 3:05 AM Page 1 Introduction to Pediatric Sleep 1 Medicine Stephen H. Sheldon FUNCTION OF SLEEP repair.5 This hypothesis proposes that certain somatic and/or cerebral deficits occur as a result Although sleep has been studied subjectively and of wakefulness, and sleep allows or promotes objectively for more than 100 years, the exact physiologic processes to repair or restore these function of sleep and its components remains deficits thereby assuring normal daytime func- elusive. Historically, physicians have recom- tioning.6-8Special focus has been placed on both mended sleep for the treatment of many disor- restoration of somatic function and the central ders. This prescription has been based on the nervous system (CNS) function. Non–rapid eye assumption that sleep provides a unique restora- movement (NREM) sleep is thought to function tive purpose. Although the relationship between in reparation of body tissue and REM sleep in the immune system and sleep may be important restoration of brain tissue. Supporting evidence, with many clinical implications, no study has however, is indirect. Napping, when its timing documented that sleep cures anything.1 and duration are designed properly, has the Circadian rhythms of various biologic processes, potential to improve waking function. Even brief for example the immune system, appear to be napping of less than 30 minutes in duration modulated by sleep, and lymphocyte functions counteracts decreased alertness and performance are dramatically altered at sleep onset and during under conditions of sleep deprivation.8a The sleep.2 Specific pokeweed mitogen response and role of NREM sleep in repair of somatic tissue natural killer cell activity are altered by sleep in comes from investigations that have shown the healthy young men. Interleukin-1–like activities following: are followed by interleukin 2–like activities dur- ing sleep, and interleukins-1 and -2 are disrupted 1. Slow-wave sleep (SWS) increases following by sleep deprivation.3 Insomnia has been shown sleep deprivation.9 to be associated with nocturnal sympathetic 2. The percentage of SWS is increased during arousal and declines in natural immunity, includ- the developmental years.10 ing a decrease in natural killer cell response.3a 3. Total sleep duration increases with body Narcoleptic patients present disordered diurnal mass.11 patterns of immune function;4however, the clin- 4. Release of growth hormone occurs at sleep ical effects that these changes produce or how onset and peak levels occur during SWS in they may be therapeutically modified are prepubertal children.12 unknown. 5. The release of many endogenous anabolic Theories of sleep function fall into several steroids (prolactin, testosterone, and luteiniz- major categories, with many overlaps. An under- ing hormone) occurs in relation to a sleep- standing of these hypotheses provides a basis for dependent cycle.13,14 comprehension of the varied effects that disor- 6. The nadir of catabolic steroid release, such as dered sleep may have on health and disease. corticosteroids, occurs during the first hours of sleep, coincident with the largest percent- age of SWS.15 Restoration Theory 7. Increased mitosis of lymphocytes and In 1946 Sherington suggested that sleep was a increased rate of bone growth occur during state required for enhanced tissue growth and sleep.16 1 Ch01.qxd 1/25/05 3:05 AM Page 2 2 Chapter 1 Introduction to Pediatric Sleep Medicine 8. There is a gradual increase in SWS percentage dolphins appear to sleep, slow-wave patterns are of total sleep time in response to a graded seen over a single hemisphere at a time, while increase in physical exercise.17 the other hemisphere shows waking rhythm.24If the evolutionary theory of sleep is true, animals However, other observations might suggest with highly complex CNS function, such as the an influence of sleep on a physiologic process dolphin, should follow this pattern. It stands to rather than a direct effect. For example, while reason that if the dolphin slept in the same man- peak rates of cell division occur during sleep, ner as the dog, cat, and human, survival in its they do not appear to be due to sleep itself. aquatic environment would be impossible. Increased mitosis is demonstrable after a night Skeletal muscle atonia during REM sleep (as cur- without sleep and is positively influenced by oral rently understood) would result in drowning. glucose load and negatively influenced by corti- Therefore, the lifestyle and environment of the sol secretion.18 Similarly, in adolescents and dolphin play a much more significant role in the adults, somatomedin levels are the highest dur- pattern of sleep development in these species ing wakefulness, not during sleep as it is in pre- than phylogeny. pubertal children.19 In some species, sleep may function to On the other hand, REM sleep—characterized enhance survival. Animals that graze for food by intense CNS activation—has been thought to tend to sleep in bursts over a short period of function in the restoration of CNS function. It time, a behavior that may provide the time may have evolved in order to “reprogram” innate needed for sufficient food-seeking while protect- behaviors and to incorporate learned behaviors ing the animal from predators.25 Carnivorous and knowledge acquired during wakefulness.20 animals who do not require large amounts of The synthesis of CNS proteins is increased during time for foraging and who are relatively safe from REM sleep.21This sleep state also appears in sig- predation tend to sleep for long periods of time. nificantly higher proportions in the fetus and Sleep may also be an instinctive behavior, a newborn, gradually decreasing over the first few patterned response to stimuli that conserves years of life. Increased protein synthesis during energy, prevents maladaptive behaviors, and pro- REM sleep may be critical in the development of motes survival.26 According to the evolutionary the CNS. theory of sleep, cortical activation in REM sleep may perform additional survival functions.27 Evolutionary and Adaptive Theories Energy Conservation Theory Development of many physiologic functions fol- Sleep may function to conserve energy. In fact, lows an orderly progression that mirrors phylo- mammalian species exhibit a high correlation genetic development. It has been suggested that between metabolic rate and total sleep time.28 the development of sleep in the human organism This view states that energy reduction is greater also follows this same phylogenetic pattern. during sleep than during periods of quiet wake- Evidence for this theory is scant. Animals sleep fulness and that sleep provides periods of in many different ways, often influenced more enforced rest, barring the animal from activity by the environment and lifestyle than by evolu- for extended periods of time. Endothermic ani- tion of the species.22 SWS and REM sleep mals exhibit SWS. During NREM sleep, endoge- rebound are characteristic features seen after nous thermoregulation continues, though sleep deprivation in the dog, cat, rabbit, and functioning at levels below those of wakefulness. human.23 Definitive REM sleep, however, has Poikilothermic species, on the other hand, do never been documented in the dolphin. not exhibit clear SWS patterns. It is doubtful, Dolphins do not have a pulmonary reflex to however, that this theory explains the function hypoxemia; therefore, they have complete, vol- of sleep in humans. Reduction in metabolism untary control of breathing, and sleep would that occurs during sleep is minimal. Although presumably be associated with impaired neu- the hypothesis is intriguing, energy conservation rorespiratory control. Actually, dolphins appear theory has been disputed and evidence exists to exhibit hemispheric sleep. That is to say, when that an increase in sleep time does not correlate Ch01.qxd 1/25/05 3:05 AM Page 3 Introduction to Pediatric Sleep Medicine Chapter 1 3 with increased metabolic rate.29,30 It has been Theories on the function of REM sleep and shown that there is only an approximately 8 to dreaming, with which it has a contingent rela- 10% reduction in metabolic rate during sleep tionship, remain diverse. Facilitation of memory when compared with relaxed wakefulness. This storage, reverse learning, anatomic and func- would be insignificant when considering an tional brain maturation, catecholamine restora- adult human’s basal metabolic expenditure. tion, and others have been postulated.35 Growing evidence supports the idea that sleep following a learning experience is critical to Learning Theory memory formation. Studies suggest that infor- A particularly interesting theory of the function mation acquired during wakefulness is reacti- of sleep centers on the role of sleep in the process vated and possibly consolidated during of learning and memory. A significant body of subsequent REM sleep.36 Several brain areas knowledge exists which suggests that retention have been shown to be activated during of new information depends on activation of sequence learning when awake and during sub- some brain function that occurs at a critical sequent REM sleep.37 This activation suggests period after the registration of this informa- that REM sleep participates in the reprocessing tion.31,32Two pivotal phases appear to exist. The of recent memory traces.38 Regional cerebral first one is “consolidation.” Medication that reactivation during post-training REM sleep is causes stimulation of the reticular activating sys- not related simply to the acquisition of basic tem and cortical excitation during the first 90 visuomotor skills during prior practice of a serial seconds after acquisition of new information reaction time task but rather to the implicit appears to enhance memory and increase reten- acquisition of the stimulus sequence. REM sleep tion. Although the consolidation phase of learn- is deeply involved in the reprocessing and opti- ing is important, it cannot be considered mization of high-order information contained in definitive for fixation of information, since pro- the material to be learned. Additionally, the level cessing continues for a long period of time. of acquisition of probabilistic rules attained The second critical phase of information pro- before sleep correlates with an increase in cessing seems to occur during sleep, specifically regional cerebral blood flow during subsequent REM sleep. Two theories have been proposed, REM sleep. This suggests that post-training cere- one based on the passivehypothesis (unlearning bral reactivation is modulated by the strength of theory) and the other on the active hypothesis, the memory traces developed during the learn- which suggests that there are active consolida- ing episode.38 tion mechanisms. An active process is supported Interestingly, learning of some perceptual by the following facts: Considerable brain activ- skills has been shown to depend on the plasticity ity occurs during this phase of sleep, in which of the visual cortex and to require post-training brain oxygen consumption increases, there is an nocturnal sleep.39Sleep-dependent learning of a increase in cerebral blood flow, and there is texture discrimination task can be accomplished intense activity of cortical and reticular neurons in human subjects having only brief (60- to 90- indicating an active, functional process. minute) naps containing both NREM sleep and Over the past 50 years, the beneficial effects REM sleep. of sleep on the retention of memories acquired Newborn infants preferentially orient to face- during wakefulness have been documented.33,34 like patterns at birth, but months of experience REM sleep appears to have special significance. with facial observations are required for full face- Despite evidence from animal and human stud- processing abilities to develop.40 Models gener- ies, the exact function of REM sleep in child- ally assume that the brain areas responsible for hood development and learning remains newborn orienting responses are not capable of unknown. Diverse reasons have been proposed learning and are physically separate from those for children’s learning difficulties, but no single that later learn from real faces. Newborn face- factor appears to be consistent for all individu- orienting may be the result of prenatal exposure als. Most diagnostic and treatment protocols of a learning system to internally generated have empirically focused on the child’s daytime input patterns, such as those found in ponto- capabilities. geniculo-occipital (PGO) waves during active Ch01.qxd 1/25/05 3:05 AM Page 4 4 Chapter 1 Introduction to Pediatric Sleep Medicine (REM) sleep. Neonates spend about 18 hours Flexible cognitive processes are regarded as asleep per day, at term, and about 50% of this fundamental to problem solving and creativity. time is spent in active/REM sleep. Preterm REM sleep has been shown to be associated with infants spend considerably more time in active creative processes and abstract reasoning, with sleep. A combination of learning and internal increased strength of weak associations in cogni- patterns is an efficient way to specify and tive networks.43 When early and late REM and develop circuitry for facial perceptions.40 This NREM awakenings are assessed, a dissociation prenatal learning can account for the newborn becomes evident, with NREM-awakening task preferences for schematic and photographic performance becoming more REM-like later in images of faces, providing a computational the night but REM-awakening performance explanation for how genetic influences interact remaining constant. The neurophysiology of REM with experiences to construct a complex adap- sleep, therefore, represents a brain state more tive system. amenable to flexible cognitive processing than Sleep loss adversely affects certain types of that of NREM sleep. cognitive processing, particularly associative The role of sleep in the development of the memory.41 Long-term potentiation represents a CNS and neural circuitry may be extremely putative cellular basis for learning and memory important. Kisley and colleagues showed that consolidation. The influence of sleep depriva- normal, young infants exhibited significant tion has been shown to result in the delay of response suppression.45 A correlation between maximal induction, and the degradation of the increasing age and stronger response suppres- maintenance phase of long-term potentiation sion was also uncovered, even within an age may represent the sleep deprivation–induced range restricted to 1 to 4 months. These data impairment of the underlying neurochemical suggest that neuronal circuits underlying sen- mechanisms normally responsible for memory sory gating are functional during very early post- acquisition. natal development. Studies relating sleep states to memory Minor neurologic and EEG abnormalities have processes typically present learning material to been described in children with “hyperactivity” participants and then examine recall ability syndrome.46These abnormalities have been asso- after intervening sleep or sleep deprivation.42 ciated with specific or global learning difficulties, Most studies have utilized either sleep record- and the syndrome has previously been described ings or sleep deprivation after a learning task. as “minimal cerebral dysfunction.” However, neu- Cueing and positron emission tomography have rologic and EEG abnormalities associated with also been utilized. Data strongly suggest that this hyperactivity syndrome have been shown to REM sleep is involved in the efficient memory be nonspecific and variable,47resulting in a change processing of cognitive procedural material but of the name of the syndrome to attention deficit not declarative material. There are some data, hyperactivity disorder (ADHD). however, which support the contention that It is noteworthy that of the 15 reading-dis- SWS or NREM sleep is necessary for declarative abled (dyslexic) children studied by Levinson, memory consolidation. Additionally, the length 97% revealed evidence of cerebellar-vestibular of the NREM-REM cycle may also be important (C-V) dysfunction. Ninety-six percent of 22 for declarative memory. Stage 2 NREM sleep blinded neurologic examinations and 90% of 70 may also be involved in memory for motor pro- completed electronystagmograms indicated sim- cedural but not cognitive procedural tasks.42 ilar C-V dysfunction.48 Ottenbacher and associ- After declarative learning tasks, the density of ates explored the relationship between vestibular sleep spindles is significantly higher than that function, as measured by duration of postrota- with a nonlearning control task and is greatest tory nystagmus, and human figure–drawing abil- during the first 90 minutes of sleep.43 Spindle ity in 40 children labeled as learning disabled.49 density also correlates with recall performance Chronologic age and postrotatory nystagmus both before and after sleep. These findings indi- durations shared significant amounts of variance cate that spindle activity during NREM sleep is with human figure–drawing. The variables of IQ quite sensitive to previous learning experi- and sex were not significant. DeQuiros and ences.44 Schrager have also identified vestibular dysfunc-