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date: 28 January 2020

Conclusion: Overview, Emerging Trends, and Future Directions in Sleep Research and Practice

Abstract and Keywords

This concluding chapter presents a brief retrospective of the main content areas covered in this handbook and outlines some emerging trends and expected developments for future sleep research, clinical practice, and education. Sleep is receiving increasing recognition, both in the public eye and among health-care professionals, as an essential feature of global health and as a significant public health problem. Considerable progress has been made in the short history of sleep research with some major advances in the understanding of basic mechanisms regulating sleep–wake cycles and the impact of sleep loss, and in documenting the epidemiology, pathophysiology, and treatment of sleep disorders. There is increasing evidence showing an association between sleep disturbance and sleep loss with mental (depression) and physical health (obesity, diabetes), as well as with public safety (risk of accidents). A natural extension of this work for future research will involve investigations of whether these consequences are reversible with adequate treatment. Despite major advances in basic and clinical research, this new knowledge does not always reach those who need it most—patients, health-care providers, and policy decision makers. To bridge this gap between research and practice, it will be essential in the future to find more efficient strategies to translate new knowledge and provide additional training opportunities to health-care providers, and develop broader community-based public health education about the critical role of sleep for global health.

Keywords: sleep, behavioral sleep medicine, research, interventions, therapies, trends, public health


Sleeping is a basic need comparable to that of eating, drinking, or having sex. Quality sleep is a critical dimension of both physical and mental health. As illustrated throughout this handbook, sleep is also intimately connected to several domains of human functioning such as emotions, cognitions, vigilance, and performance. Not getting enough sleep or, conversely, getting too much of it, can be a sign of a variety of sleep disorders and produce negative consequences on social, psychological, occupational, and physical functioning. In this concluding chapter, we present a brief retrospective of the main content areas covered in this handbook, summarize recent advances and emerging trends in the sleep field, and outline expected directions for future developments regarding research, clinical practice, and education.


Sleep is a very broad and interdisciplinary field that has attracted a great deal of research interest, initially (i.e., 1950s) from psychology and the neurosciences and, more recently (i.e., since the 1980s), clinical interest has emerged from various medical and health-related disciplines (neurology, pulmonology, psychology, psychiatry, dentistry, nursing). Despite its critical importance to health, the sleep field is a relatively young discipline, and much of what we know about sleep, its regulation, functions, and disorders has been discovered in the last 50–60 years. With this handbook we have attempted (p. 865) to summarize the knowledge base in critical areas of sleep and sleep disorders. Because the boundaries of the subject matter are almost infinite, we have selected topics likely to be of particular interest to the field of psychology. The main content areas were divided into three broad sections, organized along a loosely defined conceptual framework of normal sleep, abnormal sleep, and sleep in special populations.

Section I and its first three chapters covered the basics of normal sleep, its characteristic cycles throughout the night, homeostatic and circadian mechanisms regulating sleep and wakefulness, and the functions of sleep through an evolutionary perspective. The next several chapters examined sleep in relation to early human development, the impact of sleep loss on various aspects of performance, and the relationships of sleep to emotions and cognitions. As sleep is closely related to several altered states of consciousness, three chapters described its connection with dreaming, psychopathology, and psychotropic drugs. We then took more of a sociological perspective and examined the relationship of sleep to society, gender, and public health and safety issues, and concluded that section with a chapter on sleep and the psychology curriculum.

Section II was concerned with abnormal sleep. The first few chapters summarized the epidemiology of sleep complaints and the public health and economic burden of sleep disorders. One chapter dealt with the forensic aspects of sleep disorders, two chapters summarized the main schemes for classifying sleep/wake disorders, and another outlined a typical protocol for assessing sleep–wake complaints. The next group of chapters focused on the main sleep disorders encountered in clinical practice, with a particular emphasis on those conditions most likely seen by mental-health practitioners—insomnia; sleep disorders associated with psychiatric, medical, and substance use disorders; parasomnias (nightmares, night terrors, and somnambulism); circadian rhythm disorders; and then the more medically based sleep disorders such as sleep apnea, narcolepsy, and sleep-related movement disorders. For each of these, the main clinical features were described, along with a discussion of etiology and differential diagnosis; treatment options, with an emphasis on psychological and behavioral approaches, were also described.

Section III provided a developmental perspective on sleep and sleep problems in childhood, adolescence, and late life. The nature of sleep problems in each life cycle was discussed along with an overview of prevalence, etiology, assessment, and treatment modalities specific to each population. Following a similar structure, the last three chapters described sleep disturbances in special populations—learning disability/mental retardation, brain injury, and chronic pain.

Emerging trends and recent advances

Despite its relatively short history, considerable progress has been made in the field of sleep and sleep disorders research over the past few decades. While it is beyond the scope of this concluding chapter to even attempt to summarize these advances, many of which were described in previous chapters, we will outline some emerging trends in anticipation of future developments in the field.

In terms of basic sleep needs and functions of sleep, we have a much better understanding of the profound impact of sleep loss on vigilance, mood, and performance, both in children at school and in adults on the road and in the workplace. For instance, it is now well documented that early school start times, combined with lifestyle factors such as late bedtimes, contribute to significant sleep loss in children and adolescents and impair academic functioning (see Wolfson & O’Malley, Chapter 34). The impact of cumulative sleep loss has been well documented among several groups of workers and has shown increased risks of road accidents among truck drivers, increased numbers of medical errors among hospital staff, and even increased risks of breast cancer among female shift workers (see Akerstedt & Kecklund, Chapter 12).

Major discoveries on the neurobiology of sleep have been made in the recent past, including the discovery of hypocretin/orexin and its role in sustaining wakefulness. This discovery has had direct implications for the diagnosis and treatment of a debilitating sleep disorder such as narcolepsy (Dauvilliers & Bayard, Chapter 31).

The identification of “clock genes” (Dijk, Chapter 2) is another important discovery that has improved our understanding of chronobiological mechanisms regulating sleep–wake cycles and of circadian-based disorders such as advanced sleep phase and delayed sleep phase syndromes. Basic and clinical research has also provided a better understanding of the clinical features, pathophysiology, and treatment of sleep disorders such as restless legs syndrome and REM behavior disorder. As just one example, longitudinal studies have documented the potential role of REM behavior disorder as a precursor of some neurodegenerative diseases (e.g., Parkinson’s) in late (p. 866) life (Mahowald & Schenck, 2009). The addition of these two disorders (RLS and REM behavior disorder) to the upcoming DSM-5 is a testimony of such advances (American Psychiatric Association, 2010).

There is growing evidence of an association between sleep loss/disturbance and physical and mental health. Laboratory and epidemiological studies have documented a link between short sleep and obesity and diabetes (Van Cauter, Spiegel, Tasali, & Leproult, 2008) and, possibly, with increased mortality risks (Vgontzas et al., 2010). Likewise, insomnia has been shown to increase the risk for depression (Cole & Dendukuri, 2003; Riemann & Voderholzer, 2003) and hypertension (Suka, Yoshida, & Sugimori, 2003); cumulative sleep loss has also been associated with decreased vigilance and impaired performance, as well as with increased risk for accidents on the road and at work. This research has increased awareness in the general public and in the health-care community of the importance of sleep and given some credibility to the field about the value of treating sleep disorders.

Another major step forward in the field is the recognition of the reciprocal influence between sleep disturbances and psychopathology. Whereas not too long ago, sleep disturbance was viewed strictly as a symptom of an underlying psychopathology (e.g., anxiety, depression), it is now well recognized that insomnia, for instance, can directly influence the onset and course of another psychiatric disorder such as major depression (National Institutes of Health, 2005). Combined with the evidence that sleep disturbance is a common residual symptom even after successful treatment of a coexisting depression (Nierenberg et al., 2010), and that such residual symptom can enhance the risk of relapse, these findings have led to major changes in both the conceptualization and treatment of insomnia.

There has been indeed an important change of paradigm in conceptualizing insomnia, particularly when it presents with another psychiatric or medical disorder. Given the difficulty in determining whether insomnia is the cause or consequence of a coexisting condition, and because the nature of this relationship may change over time, it is now suggested to view such condition as comorbid rather than secondary (National Institutes of Health, 2005). Taking this new conceptualization a step further, the DSM-5 work group, mandated to revise diagnostic criteria for sleep disorders, has recommended eliminating the distinction between primary and secondary insomnia (American Psychiatric Association, 2010). Accordingly, an insomnia disorder diagnosis is made once criteria are met, but the clinician no longer has to make an attribution as to whether it is primary or secondary in nature. This change in paradigm is likely to improve accuracy of insomnia diagnosis and encourage clinicians to treat insomnia directly rather than focusing exclusively on the comorbid condition. The impact of this change is already evident by the increasing number of clinical trials focusing on the treatment of comorbid insomnia in patients with various psychiatric and medical disorders (e.g., depression, anxiety, pain, cancer) (Smith, Huang, & Manber, 2005).

Significant advances were made in the treatment of sleep disorders over the last two to three decades. New medications with improved risks/benefits ratios have been developed for insomnia (e.g., zolpidem, eszopiclone), narcolepsy (e.g., modafinil), and restless legs syndrome (e.g., mirapex). With regard to insomnia, we have moved from the eras of chloral hydrate and barbiturates to benzodiazepines and benzodiazepine-receptor agonists and, more recently, to the development of new molecules with different mechanisms of actions (e.g., melatonin agonists, orexin antagonists, serotonergic agents). The design of a mechanical device such as CPAP (continuous positive airway pressure) for treating sleep apnea is probably the most important discovery in clinical sleep medicine. The advent of dental devices is another therapeutic approach that may be promising for some patients, although more randomized controlled trials are needed to document its efficacy.

The clinical management of sleep disorders with psychological and behavioral approaches has also witnessed major advances. There is solid evidence that CBT is as effective as medication and produces more durable benefits over time (National Institutes of Health, 2005). More importantly, CBT is receiving increasing recognition and acceptance as the mainstream intervention for a sleep disorder that has traditionally been treated almost exclusively with medications. In addition to insomnia, there is also increasing evidence that nightmares can be treated effectively with behavioral approaches (i.e., imagery rehearsal) (Krakow et al., 2001); this is an important advance for our field given the high prevalence of this condition, particularly in association with post-traumatic stress disorder (Germain & Nielsen, 2003). These are just a few major advances in the field in the last two decades.

Future directions

Despite significant advances in the field, there are many remaining questions and challenges about the (p. 867) functions of sleep, its mechanisms, and the treatment of sleep disorders. Several work groups and advisory committees (National Institutes of Health, 2005; Riemann et al., 2011; The National Center of Sleep Disorders Research, 2003) have proposed agendas for future research. In this concluding section, we summarize some of these recommendations and outline our own views of future developments deemed important to move the field forward.



Population-based studies are needed to build normative sleep databases for different age groups across the life span. Such databases (similar to a table of ideal body weights) would be extremely helpful for defining “normal sleep.” Having a range of normal values for sleep parameters such as total sleep time, sleep onset latency, and wake after sleep onset would provide benchmarks to define individual differences and determine when certain sleep patterns become abnormal. For example, would the standard (yet arbitrary) 30-minute criterion used to define sleep onset or sleep maintenance insomnia be supported by such normative data? Likewise, is waking up at 4:00 a.m., after 5 or 6 hours of quality sleep, “abnormal” and in need of treatment?

Longitudinal studies are also needed to document the natural history of sleep disorders, particularly insomnia, its incidence, risk factors, and rates of persistence, remission, and recurrence over time. It is also important to gain a better understanding of factors moderating the course of sleep disorders over time. This type of research is important, as it could lead to the design of more efficient prevention/intervention programs to be implemented early in the course of the disorder and hence minimize the risk of chronicity and morbidity.

Despite the growing evidence of an association between sleep disturbance with physical (obesity, diabetes) and mental health (depression), most of the evidence supporting these associations is cross-sectional. The next step will be to use a longitudinal approach to document more precisely the long-term impact of sleep loss and sleep disorders, independently of comorbid conditions, on both physical and mental health, as well as on public safety. More importantly, controlled clinical trials should also examine whether such negative health outcomes are reversible with appropriate interventions.

There is now solid evidence that sleep loss produces negative impacts on health and that sleep disturbances increase with aging. Longitudinal research to document the relationship between sleep and aging and the impact of sleep disturbances on the development of age-related neurodegenerative diseases (e.g., dementia, Parkinson’s disease) would be very informative.


As we are just beginning to unravel the causes of some sleep disorders (e.g., sleep apnea, narcolepsy, restless legs syndrome), much research still remains ahead to gain a better understanding of the etiology of most sleep disorders. For example, the pathophysiology of insomnia is still poorly understood and it remains unclear whether hyperarousal, a core feature of the disorder, is a cause, a risk factor, or an epiphenomenon of insomnia. More research is needed to disentangle the psychological and biological underpinnings of chronic insomnia and to validate current theoretical and conceptual models of insomnia. With recent advances in sleep research instrumentations and technology, future studies would also benefit from integrating modern methodological approaches (animal studies, molecular biology, neuroimaging, neurophysiology) to further investigate the etiology of insomnia (Riemann, Spiegelhalder, et al., 2010).

Genetic studies are also needed to understand risk factors and vulnerability of sleep disorders. While the genetic contribution to sleep disorders such as narcolepsy and restless legs syndrome is well documented, there is still little evidence to support the validity of current insomnia phenotypes (e.g., psychophysiological, idiopathic, paradoxical). Additional research is needed to refine and validate these phenotypes and move to the next step of genetic testing.


Despite significant advances in the management of sleep disorders and the developments of improved medications for insomnia, narcolepsy, and restless legs syndrome, the choice of pharmacological agents for any single sleep disorder remains rather limited. Continued research efforts are needed to develop new drugs with greater benefits and fewer side effects. With regard to sleep apnea treatment, the advent of CPAP is a major advance but, despite strong evidence of efficacy and reduced morbidity associated with this treatment, compliance with CPAP device remains problematic for many patients (particularly those with insomnia symptoms). Further refinements in the device will be necessary to increase acceptance and compliance with such intervention.

(p. 868) Significant progress has been made in the management of insomnia, by far the most prevalent sleep disorder and the condition most likely to be encountered by mental-health practitioners. There is good evidence that medication (i.e., benzodiazepine-receptor agonists) is effective for the short-term management of insomnia and, to a lesser extent, for chronic insomnia (Riemann & Perlis, 2009). There is also solid evidence that psychological and behavioral therapies are as effective as medication and produce more durable benefits over time (National Institutes of Health, 2005).

Despite these advances in therapeutic approaches, there is a need for further treatment outcome research addressing issues of efficacy, effectiveness, compliance, and cost benefits. For example, although psychological and pharmacological therapies benefit a large proportion of patients with insomnia, neither of these modalities is effective or acceptable for all patients. In addition to improving the effectiveness of our therapeutic approaches to managing insomnia, future research should also examine other issues of direct relevance to clinical practice. For example, when should we initiate treatment for insomnia? What should be our first-line therapy and, for those who fail to respond, what are the alternative second-stage therapies? How should we implement dual therapies for comorbid sleep disorders? For instance, when treating insomnia comorbid with major depression or with generalized anxiety disorder, should we initiate therapies for both conditions concurrently or sequentially? What is the impact of treating insomnia on the course of the comorbid condition?

There is also a need to evaluate the impact of treating sleep disorders beyond reduction of sleep symptoms. There is already strong evidence that treating a life-threatening disorder such as obstructive sleep apnea improves cardiovascular functions and reduces mortality. There is a critical need to demonstrate that treating other sleep disorders, for instance insomnia, can also have a significant impact on health-related outcomes. Equally important will be the demonstration that treating sleep disorders reduces the overall economic burden on the health-care system. For instance, population-based studies (Daley, Morin, LeBlanc, Grégoire, & Savard, 2009) have documented the high costs of insomnia in terms of burden of illness (i.e., work absenteeism, reduced productivity, accidents), expenses up to 10 times higher than the direct costs for treating insomnia (i.e., consultations, medications). The next logical step would be to demonstrate that spending x dollars (e.g., $500) for treating a sleep disorder will save y dollars ($1,000) at the end of the year in terms of reduced absenteeism, improved productivity, and decreased utilization of health-care services. Only with such demonstrations will public health officials take sleep disorders seriously when it comes to allocating resources for treatment and education. Cost-benefits and cost-effectiveness studies are clearly warranted.

Circadian-based sleep disorders have received relatively less attention than other sleep disorders, particularly with regard to interventions. Despite significant progress in understanding the basic chronobiological features of some of these disorders (e.g., advanced sleep phase and delayed sleep phase disorders), little is known about clinical management. Of course, bright light therapy and melatonin represent promising therapeutic approaches, but there is a need for clinical research examining the efficacy of these interventions, as well as behavioral approaches, for the management of these disorders, which are particularly prevalent in adolescents (delayed sleep phase) and older adults (advanced sleep phase).

Another line of research that warrants further attention is the development of behavioral strategies specifically designed to improve compliance with the different therapies prescribed for managing sleep disorders. Poor treatment adherence is not unique to the management of sleep disorders, but it is a major impediment to successful outcomes when treating sleep apnea with CPAP, circadian disorders with bright light therapy, or even when prescribing medications for insomnia.

Clinical practice

Despite considerable advances in the treatment of sleep disorders, there are still major gaps between available research evidence and current clinical practice. For instance, even with the strong evidence-based supporting psychological and behavioral approaches to treating insomnia, medication therapy is by far the most frequently used therapeutic approach in clinical practice. This gap is partly due to the fact that most people with sleep problems seek treatment from their family physicians before consulting with a mental-health provider, a practice that often dictates the first-line treatment. There is also a supply problem in that very few health-care providers, even fewer mental-health providers, have received adequate training for treating sleep disorders.

Even with the very significant increase in the number of sleep clinics in the last 20 years (p. 869) (especially in North America), very few of these clinics offer comprehensive diagnostic and treatment services for sleep disorders other than sleep apnea. Because insurance reimbursements is often restricted to services for medical conditions such as sleep apnea, most sleep clinics are in fact sleep apnea clinics, with no or minimal services for other sleep disorders.

With the high prevalence of some sleep disorders, it is unrealistic to expect that family doctors can respond adequately to this demand. Given some important barriers to treatment (e.g., limited number of health-care providers with adequate expertise), new treatment delivery models (e.g., Internet-based) are being developed and validated. While this e-health movement is becoming increasingly popular and, indeed, facilitates transfer of new knowledge to health-care providers and the general public, this is no panacea for treating all individuals with sleep disorders. Such a treatment delivery model is best seen in the context of a larger, stepped-care model (Espie, 2009) and as complementary to the more traditional face-to-face intervention. There will always be a need for well-trained, competent, and in-person therapists to conduct clinical assessment and therapy of sleep disorders. With the recent emergence of a new behavioral sleep medicine specialty (McCrae, Taylor, Smith, & Perlis, 2010; Taylor, Perlis, McCrae, & Smith, 2010), it is hoped and expected that additional educational and training opportunities will become available and increase the number of clinicians outside the traditional medical fields with expertise in the management of sleep disorders.

Education/public health

Considerable progress has been made in understanding sleep and sleep disorders, yet this new knowledge has not always reached potential users such as health-care practitioners, decision makers and employers, and the general public. With the growing evidence that sleep loss and sleep disorders are associated with negative health outcomes, one would hope to witness more concerted public health efforts and initiatives to educate major stakeholders in the benefits of good quality sleep for mental and physical health, as well as for public safety. Examples of important themes/targets for such public health education initiatives are outlined below.

Sleep In Children And Adolescents

The extent of sleep curtailment due to early start-up school times among children and adolescents is well documented, as is its impact on cognitive functioning, mood, and academic performance. Some educational initiatives (Garfield Star Sleeper) may have raised public awareness of this new knowledge in the past, but it is not entirely clear whether such programs have in fact led to changes in school schedules and policies and in parenting practices. Nonetheless, there is a critical need for further public health education programs to inform parents, teachers, and school officials of critical circadian and homeostatic principles to adhere to in order to create the best learning circumstances for children and adolescents.

Sleep In Late Life

A similar plea could be made for targeted education of caregivers at the other end of the life span. It is well recognized that sleep becomes more fragmented and of poorer quality in later life. Such changes take place gradually, even among otherwise healthy individuals, but older adults with demented illnesses are particularly vulnerable to disrupted sleep patterns. Although these sleep disruptions are directly related to the extent of the neurological degenerative process, the environment in residential care facilities, which is often not very conducive to sleep, can further deteriorate sleep quality. For instance, excessive amounts of time spent in bed interfere rather than promote sleep. Limited exposure to daylight can also worsen sleep. There is a need for clear guidelines intended for caregivers and staff of residential facilities to promote better quality sleep at night (i.e., restrict time spent in bed, minimize daytime napping, provide opportunities for exposure to daylight, exercise).

Fatigue, Sleepiness, And Drowsy Driving

Sleep has important implications for public health and safety. Fatigue and sleepiness are involved in about 20%–25% of all road accidents with injuries or deaths and, in more than half of these accidents, the driver has slept less than six hours the night before (Société de l’assurance automobile du Québec, 2010). It is estimated that with about 18 hours of sustained wakefulness, a driver’s performance is equivalent to that of someone with a 0.05 blood alcohol level. Thus, fatigue and sleepiness directly impair a driver’s attention, vigilance, and reaction time, increasing significantly the risk of road accidents. The sleep debt accumulated under such circumstances is often related to lifestyle factors such as sleep habits and work schedules. These facts underscore the need for public education about (p. 870) the critical importance of adequate sleep to reduce the risk of road accidents. Public advertisement campaigns about the risks of fatigue on the road similar to those designed to enhance awareness of the risks associated with speeding or drinking and driving are very much needed.

Sleep As A Critical Dimension Of Global Health

With increasing public awareness of the negative impact of poor sleep and insomnia on health, the time has come to take a much more proactive stance in promoting sleep as a critical determinant of health. To this end, it may be more efficient to move from a disease-focus model to a health-promotion model and emphasize how healthy sleep is an essential ingredient of a global health-promotion plan. As a first step, it would be important to provide factual information about normal sleep and about the number of hours of sleep needed to stay alert and healthy. Likewise, rather than emphasizing only the negative consequences of sleep disturbances, it may be more efficient to highlight the benefits of good sleep habits and quality sleep on health and quality of life. Large, community-based, public health education programs are needed to raise awareness of the critical importance of sleep. We may need to draw from the very efficient direct-to-consumer marketing strategies used by pharmaceutical companies in order to catch the public’s attention when preparing such sleep health-promotion campaigns. Hopefully, sleep and good sleep habits will become in the public eyes as important to a healthy lifestyle as a balanced diet and a regular exercise regimen.


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