This large, population-based study demonstrates that sleep misperception is prevalent in chronic insomniacs with objectively measured normal sleep duration but not in those with short sleep duration. Furthermore, sleep misperception is associated with depressive, anxious-ruminative personality traits and poor coping resources. These findings are independent of other factors frequently associated with insomnia or objective sleep duration, such as gender, age, race, education, obesity, SDB, hypertension, or depression.
Early studies of sleep misperception suggested that underestimation of sleep duration was a generic trait in insomnia (27
). This view is reflected in the DSM-IV text of the diagnosis of “primary insomnia” (3
). In contrast, the ICSD-2 states that “paradoxical insomnia” (i.e., “sleep state misperception” or “subjective insomnia”) is a rare condition accounting for fewer than 5% of all insomnia patients (6
). In the present study, only insomniacs with normal sleep duration showed a significant underestimation of sleep duration. A recent review by Edinger and Krystal (5
) showed that the relative prevalence of “subjective insomnia/sleep state misperception” in clinical and research samples varies between 9.2% and 50%. The present study suggests that insomnia with normal sleep duration, which accounts for about fifty percent of all chronic insomniacs in the general population, is strongly associated with sleep misperception.
The factors implicated in sleep misperception among insomniacs remain unknown. For example, several studies have failed to show an altered perception of time in insomniacs (30
), suggesting that factors other than deficits in perceptual processing of time might be involved in sleep misperception. Personality traits, anxiety, rumination, pre-sleep worry (23
), and their physiological correlates (40
), have also been suggested to play a role in the underestimation of sleep duration in insomnia. The present study is the first to show that in a general population sample of chronic insomniacs sleep misperception is associated with MMPI-2 personality profiles characterized by “depressive mood, rumination, anxiety, intrusive thoughts, and poor resources for coping with stress” (22
). These personality characteristics in a discriminant analysis differentiated with a sensitivity of approximately 84% the insomniacs with sleep misperception vs. insomniacs without.
Insomniacs with short sleep duration, similarly to their respective controls, significantly overestimated their sleep duration, a finding that is consistent with previous reports where insomniacs with objectively measured short sleep displayed overestimates of sleep duration (35
). This group of insomniacs was associated with MMPI-2 profiles that reflect “depressive mood, fatigue, concerns about health and physical functioning, somatically focused anxiety, and poor health status” (22
), which is a psychological profile typical of outpatients with a medical disorder (23
). Previous reports have shown that insomnia with short sleep duration is associated with hypercortisolemia (7
), increased catecholaminergic activity (54
), sympathetic activity (55
), and medical morbidity (12
). It is very likely that the “somatic preoccupation” of these insomniacs is not “hypochondriac” in its nature, but reflects true physiological and physical changes as a result of chronic activation of the stress system. Alternatively, the activation of the stress system can be the result of physical and/or physiological sleep changes in insomnia subjects.
The distinct psychological profiles between insomnia subtypes based on objective sleep duration are consistent with previous studies in clinical samples which showed that “subjective insomniacs” have higher neuroticism (58
), higher scores on psychasthenia (7-PT) and schizophrenia (8-SC) scales (42
), higher anxiety, lower mood, more dysfunctional sleep-related cognitions (59
), and fewer somatic complaints (11
) when compared to “objective insomniacs”. Moreover, a previous cluster analytic study (38
) found 2 insomnia subtypes based only on MMPI scores: an “anxious, ruminative, cognitively disorganized” group with a predominant 273/237 code-type, fewer somatic concerns (lower hypochondriasis -1-HS- scores), more worry and intrusive thoughts, and greater concern about not sleeping, and a 231/312 code-type group with “less anxiety and cognitive turmoil”. In the present study, the differences in anxiety and ego strength between the two insomnia subgroups were modest in terms of absolute values. Nevertheless, the present study suggests that objective sleep duration is a useful marker in separating insomniacs with and without sleep misperception and their associated psychological characteristics.
In the present population-based study, controls overestimated their sleep duration. This finding is consistent with epidemiological studies showing that individuals in the general population typically overestimate sleep time (60
). The factors underlying the marked overestimation of sleep duration in controls with short sleep duration are not known or apparent and further investigation is needed.
The objective sleep duration in this study was based on one night of polysomnography, which may not be representative of the subjects’ typical objective sleep duration. However, in our previous studies, the association between objective short sleep duration and hyperactivity of the stress system in insomniacs was based on a 4 consecutive night sleep laboratory protocol, which should better represent the typical sleep profile of the subjects (7
). The consistency of the findings on the role of objective short sleep duration in predicting insomnia severity between the physiological studies with multiple night recordings (7
) and our previous epidemiological studies based on a single night recording (12
) increases our confidence about the replicability and generalizability of the present findings. In large epidemiologic studies the average objective sleep duration is about 6 hours, which is independent of whether sleep is recorded at home with polysomnography, i.e., Sleep Heart Health Study (61
), or for 3 consecutive nights with actigraphy, i.e., CARDIA study (60
), or in the sleep laboratory, i.e., Penn State Cohort (12
). Furthermore, the SHHS and CARDIA studies reported that in general population samples objective sleep duration is usually shorter by 1 hour (60
) and by 18 minutes (61
) than habitual and next-morning subjective sleep duration, respectively, which is very consistent with our findings, i.e., in the total sample mean discrepancy in habitual sleep duration was of 1.0 hours and next-morning sleep duration of 20 minutes. Thus, the consistency among these three large epidemiological studies in terms of objective sleep duration, subjective sleep duration and their discrepancy reinforces our belief that the inherent limitations of 1-night recording in large samples do not compromise the validity of the findings. In support of this view, in a recent study of clinical insomniacs based on 2-nights recording the frequency of insomniacs with sleep misperception was very similar to ours (45
). From our study, we cannot exclude the possibility that the subjective-objective discrepancy may in part reflect the response of these individuals to sleeping in an unfamiliar environment (i.e., the sleep lab vs. their home environment). Future studies should explore the association between insomnia, objective sleep duration and sleep misperception using multiple night recordings obtained in the sleep laboratory or with easier-to-use methods, i.e., actigraphy.
The field of sleep disorders medicine has attempted to define subgroups within insomnia based on etiology (i.e., primary vs. secondary), age of onset (i.e., childhood vs
. adult), and objective sleep findings (6
). Although for years sleep specialists suggested that the sleep lab was of no use in the evaluation of insomnia (1
), the previously published data on the association of insomnia combined with objective short sleep duration with the stress system (7
), the autonomic system (44
), and with medical morbidity (12
), have led us to suggest two phenotypes of chronic insomnia. The first phenotype is associated with physiological hyperarousal, i.e., short sleep duration, activation of the stress system, and significant medical sequelae, e.g., hypertension, diabetes, neurocognitive deficits and increased mortality. The second phenotype is not associated with physiological hyperarousal, i.e., normal sleep duration, normal activity of the stress system, and lack of significant medical sequelae. The present study expands on the differential characteristics of these two phenotypes. The first one is associated with a psychological profile typical of medical outpatients, whereas the second one is associated with sleep misperception and an anxious-ruminative, poor coping skills profile.
Our findings on these proposed phenotypes may have a significant impact on how we diagnose and treat insomnia. Currently, the diagnosis of insomnia is based on subjective complaints. The introduction of objective measures of sleep in the evaluation of insomnia may be of relevance for the practicing physician in terms of prioritizing intervention based on severity. Furthermore, these 2 phenotypes may respond differentially to treatment approaches. The first phenotype may respond better to treatments that primarily aim at decreasing physiological hyperarousal (e.g., cortisol) and increasing sleep duration, such as medication or other biological treatments (9
), whereas the second phenotype may respond better to treatments that primarily aim at decreasing cognitive-emotional hyperarousal (e.g., rumination) and altering sleep misperception (63
), such as sleep scheduling, behavioral experiments, cognitive restructuring, or emotion regulation techniques.
In conclusion, the present study delineates even further these two chronic insomnia phenotypes based on objective sleep duration and provides further support for their potential clinical validity and usefulness. The diagnostic validity and clinical utility of this phenotyping should be tested in prospective studies and/or with treatment interventions in chronic insomniacs.