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Journal of Clinical Sleep Medicine : JCSM : Official Publication of the American Academy of Sleep Medicine logoLink to Journal of Clinical Sleep Medicine : JCSM : Official Publication of the American Academy of Sleep Medicine
. 2022 Jul 1;18(7):1789–1795. doi: 10.5664/jcsm.9974

Negative and positive sleep state misperception in patients with insomnia: factors associated with sleep perception

Gahui Yoon 1, Mi Hyun Lee 1, Seong Min Oh 2, Jae-Won Choi 3, So Young Yoon 1, Yu Jin Lee 1,✉
PMCID: PMC9243288  PMID: 35383568

Abstract

Study Objectives:

In the present study, factors associated with sleep perception were identified by comparing clinical characteristics and polysomnographic variables between insomnia patients with negative and positive sleep state misperception (NSSM and PSSM, respectively).

Methods:

Self-reported and objective sleep measures were retrospectively collected, including the Pittsburgh Sleep Quality Index (PSQI), Beck Depression Inventory, and a questionnaire on “morning feeling” after nocturnal polysomnography in 150 patients with insomnia. Based on the misperception index (MI), participants were classified into NSSM (MI > 0, n = 115) and PSSM (MI < 0, n = 35) groups.

Results:

The PSSM group had more N3 sleep on nocturnal polysomnography than the NSSM group (P = .002). The NSSM group showed a higher PSQI score (P < .001), longer self-reported sleep-onset latency (SOL) (P = .001), and a greater SOL discrepancy (P = .001). Self-reported feelings of tiredness and morning awakenings in the morning were higher in the NSSM group (P = .029 and P = .038). The MI negatively correlated with a proportion of N3 sleep (P = .005) and positively correlated with PSQI (P < .001), morning awakenings (P = .01), self-reported SOL (P < .001), and SOL discrepancy (P < .001) in patients with insomnia. Multiple regression analysis showed that N3 sleep, PSQI, and morning awakenings were significantly associated with MI in patients with insomnia.

Conclusions:

The proportion of slow-wave sleep and self-reported measures may be associated with perception of sleep in patients with insomnia. Objective and self-reported characteristics of patients with insomnia should be carefully evaluated and managed because they may influence the perception of sleep.

Citation:

Yoon G, Lee MH, Oh SM, Choi J-W, Yoon SY, Lee YJ. Negative and positive sleep state misperception in patients with insomnia: factors associated with sleep perception. J Clin Sleep Med. 2022;18(7):1789–1795.

Keywords: insomnia, sleep state misperception, paradoxical insomnia, sleep discrepancy

BRIEF SUMMARY

Current Knowledge/Study Rationale: Sleep state misperception is common in insomnia, but comparison of negative and positive sleep state misperception using polysomnography and self-reported questionnaires on “morning feeling” are lacking. To identify factors affecting sleep perception, the polysomnography data of 150 insomnia patients who underestimated or overestimated their sleep duration were retrospectively reviewed and divided into 2 groups.

Study Impact: The proportion of slow-wave sleep, along with self-reported awakenings and usual sleep quality, may affect perception of sleep in insomnia patients. Considering their influence on sleep perception, polysomnographic variables and self-reported measures should be carefully evaluated.

INTRODUCTION

Insomnia is a common sleep disorder, affecting approximately 10% of the adult population.1 Self-reported complaints regarding the quality and quantity of sleep are crucial for diagnosing insomnia according to the Diagnostic and Statistical Manual of Mental Disorders, fifth edition, and International Classification of Sleep Disorders, third edition.2,3 Formal, objective diagnostic criteria for insomnia are lacking, and there is large variability in individual perception of self-reported sleep time; sleep misperception is essential to understand insomnia.4–6 Discrepancies between self-reported and objective sleep parameters are common in patients with insomnia, mostly due to underestimation of the total sleep time (TST) or overestimation of the sleep-onset latency (SOL) relative to objective measurements obtained using actigraphy or nocturnal polysomnography (PSG).7 In several studies, this discrepancy in patients with insomnia who reported dysfunction and distress has been investigated.8,9 In the International Classification of Sleep Disorders, first edition-revised and second edition, discrepancies between self-reported and objective sleep parameters were described as “sleep state misperception” or “paradoxical insomnia.”10,11 Although an insomnia subtype relating to this misperception was removed from the third edition, researchers are continuing to study sleep state misperception because of its commonness and clinical implications for insomnia.3,6,7

Based on the International Classification of Sleep Disorders, second edition, patients with paradoxical insomnia show a consistent and marked mismatch between self-reported and objective sleep estimations, and significant impairment in daily function.10 In a previous study on diagnostic criteria for paradoxical insomnia, a sleep time ≥ 6 hours and sleep efficiency ≥ 85% were suggested based on PSG data.12 The prevalence of sleep state misperception is 9.2–50% in patients with insomnia according to previous studies, while a systematic review reported that it varies widely, from 14% to 64%, due to the use of different criteria.6,9,13 Because of differences in definitions, it is difficult to compare the results among previous studies.6 In addition, the mechanisms underlying sleep state misperception have not yet been fully explained. In several studies, hypotheses involving specific personality traits and neurophysiological features, such as sleep microstructure, which cannot be detected using objective measures or electroencephalography (EEG), were suggested.14–16 Furthermore, the concept of “positive sleep state misperception” (PSSM) or “reverse sleep state misperception,” which refers to the tendency of patients with insomnia to overestimate their self-reported TST was suggested, while the negative sleep state misperception (NSSM) represents underestimation of self-reported TST.17,18 PSSM can be partially explained by the issues associated with mesograde amnesia and psychological distress.17,19,20

Despite heterogeneous definitions and etiologies, the concept of sleep state misperception is important for understanding insomnia, because it generally seen in individuals who complain of sleep disturbance.4,6 Furthermore, because sleep duration can be underestimated or overestimated in patients with insomnia, sleep state misperception should be conceived of as a “continuum of sleep perception,” including both negative and positive sleep state misperception. Therefore, the focus of the present study was on this “spectrum of misperception” rather than establishing cutoffs for diagnosing sleep state misperception. In addition, despite its important role in chronic insomnia,21 only few studies have investigated sleep state misperception using nocturnal PSG and self-reported measures following morning after the study. In summary, factors affecting sleep perception were investigated by comparing clinical characteristics and polysomnographic variables between NSSM and PSSM groups of patients with insomnia.

METHODS

Participants

The medical records and nocturnal polysomnographic data of patients who visited the sleep clinic of the Psychiatric Department of Seoul National University Hospital between May 2007 and July 2020 were retrospectively reviewed. All participants underwent nocturnal PSG to evaluate sleep disturbances. Participants > 18 years of age with a score ≥ 5 on the Pittsburgh Sleep Quality Index (PSQI) were enrolled in the current study. Based on the Diagnostic and Statistical Manual of Mental Disorders, fourth edition,22 participants who met the diagnostic criteria for insomnia disorder were included. Because all complaints of insomnia were > 3 months in duration, the participants also met the diagnostic criteria for insomnia disorder in the Diagnostic and Statistical Manual of Mental Disorders, fifth edition.2 Participants who had any other sleep disorder were excluded; thus, from a total of 1,085 recordings, 711 of obstructive sleep apnea (apnea-hypopnea index ≥ 5 events/h), 9 of non–rapid eye movement (NREM) parasomnia, 127 of rapid eye movement (REM) sleep behavior disorder, 61 of narcolepsy, 56 of restless legs syndrome, and 302 of patients with a periodic limb movement index score ≥ 15 on nocturnal PSG were omitted. Forty-three patients who were diagnosed with cancer or other major medical diseases (except for hypertension and diabetes mellitus), serious neurological illness such as a brain tumor or epilepsy, or serious psychiatric disorders including schizophrenia and bipolar disorder, were also excluded. Finally, the nocturnal PSG recordings of 150 patients were included in this study, which was approved by the Institutional Review Board of Seoul National University Hospital.

Polysomnography

All participants underwent nocturnal PSG (Neuvo; Compumedics, Charlotte, NC, USA) consisting of an EEG (electrodes at F3, F4, C3, C4, O1, and O2, with A1 and A2 as reference sites), electrooculogram, submental and bilateral tibialis anterior electromyogram, and single-lead electrocardiogram. A nasal sensor to measure airflow, a respiratory inductance plethysmography band to evaluate thoracic and abdominal motion, and a finger pulse oximeter for monitoring oxygen saturation were also used. All data were assessed by qualified technicians and physicians according to the manual of the American Academy of Sleep Medicine.23 Sleep parameters were calculated, including time in bed; TST; SOL; REM sleep latency; sleep efficiency; percentage of N1, N2, N3, and REM sleep stages; the apnea-hypopnea index; and the periodic limb movement index.

Self-reported measures

All participants were asked to complete self-report questionnaires that captured demographic information (age, sex, weight, and height), medical history, and current medications (before nocturnal PSG). The Korean version of the PSQI24 was used to evaluate quality of sleep over the past month, and depressive symptoms were assessed using the Korean version of the Beck Depression Inventory (BDI).25 Daytime sleepiness was measured using the Korean version of the Epworth Sleepiness Scale (ESS).26

Self-report questionnaires on sleep quality were completed by all participants on the morning after the nocturnal PSG, including self-reported TST, self-reported SOL, morning awakenings, and “morning feeling.” Participants were asked to report the number of morning awakenings. Morning feeling was assessed using a 4-point Likert scale; higher values indicate feeling more refreshed.

The misperception index and SOL discrepancy calculation

The participants were divided into 2 groups based on the misperception index (MI), which quantifies the discrepancy between self-reported TST and objective TST based on the nocturnal PSG, as used in a previous study (MI = [objective TST − self-reported TST]/objective TST).27 A positive MI value (MI > 0) indicates underestimation of sleep duration and a negative MI value (MI < 0) indicates overestimation. Participants who had a positive MI value were classified into the NSSM group and those with a negative MI value were classified into the PSSM group. To evaluate sleep misperception, the TST and SOL discrepancy was calculated by subtracting the objective nocturnal PSG variables from the self-reported sleep duration variables.

Statistical analysis

All statistical analyses were performed with SPSS software (version 23.0; SPSS Inc, Chicago, IL, USA) and a P value < .05 was considered statistically significant. The t test for independent groups and chi-square test were used for analyzing the demographic data, including age, body mass index, and sex. Analysis of covariance (ANCOVA) was used to evaluate significant differences in polysomnographic variables, PSQI and ESS scores, BDI, and morning questionnaires between the NSSM and PSSM groups, after controlling for age and sex. In addition, a partial correlation analysis was conducted after controlling for age and sex to assess the associations of the MI with polysomnographic variables, PSQI and ESS scores, BDI, and self-reported questionnaires in all participants. To identify factors significantly associated with the MI in patients with insomnia, multiple regression analysis was performed in all participants. The independent variable was MI.

RESULTS

Demographic data

Among the 150 patients with insomnia, 115 (76.7%) were classified into the NSSM group and 35 (23.3%) into the PSSM group. The demographic characteristics of the NSSM and PSSM groups are listed in Table 1. The mean age of all participants was 46.63 ± 14.67 years and 40% were men (n = 60). The patients in the NSSM group were significantly older than patients in the PSSM group (48.21 ± 14.44 vs 41.43 ± 14.43 years, P = .016).

Table 1.

Demographic characteristics and polysomnographic variables of the NSSM and PSSM groups.

Variables Total (n = 150) NSSM (MI > 0, n = 115) PSSM (MI < 0, n = 35) P
Age (years) 46.63 ± 14.67 48.21 ± 14.44 41.43 ± 14.43 .016a
Sex, male (n, %) 60, 40 47, 40.9 13, 37.1 .694b
BMI (kg/m2) 24.34 ± 10.58 24.33 ± 11.89 24.37 ± 3.97 .985a
TIB (min) 490.65 ± 33.62 489.84 ± 34.27 493.30 ± 31.73 .543c
TST (min) 399.08 ± 58.31 396.14 ± 58.42 408.71 ± 57.76 .587c
SOL (min) 18.27 ± 22.10 18.19 ± 22.55 18.56 ± 20.87 .776c
REML (min) 122.01 ± 75.65 123.10 ± 78.07 118.41 ± 67.99 .861c
SE (%) 81.78 ± 12.01 81.33 ± 11.90 83.2 ± 12.41 .791c
N1 sleep (%) 14.03 ± 8.27 14.13 ± 7.10 13.71 ± 11.44 .745c
N2 sleep (%) 50.56 ± 13.38 51.24 ± 12.00 48.31 ± 17.19 .353c
N3 sleep (%) 8.41 ± 13.09 6.42 ± 10.31 14.94 ± 18.38 .002c
REM (%) 18.65 ± 7.88 18.86 ± 8.33 17.96 ± 6.22 .349c
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at Test for independent groups. bChi-square test. cANCOVA adjusted for age and sex. ANCOVA = analysis of covariance, BMI = body mass index, MI = misperception index, NSSM = negative sleep state misperception, PSSM = positive sleep state misperception, REM = rapid eye movement sleep, REML = rapid eye movement sleep latency, SE = sleep efficiency, SOL = sleep-onset latency, TIB = time in bed, TST = total sleep time.

Polysomnographic variables

ANCOVA was adjusted for age and sex to compare the polysomnographic variables between the 2 groups (Table 1). Significant differences were not observed in TST (396.14 ± 58.42 vs 408.71 ± 57.76 minutes, P = .587), SOL (18.19 ± 22.55 vs 18.56 ± 20.87 minutes, P = .776), REM sleep latency (123.10 ± 78.07 vs 118.41 ± 67.99 minutes, P = .861), or sleep efficiency (81.33 ± 11.90% vs 83.27 ± 12.41%, P = .791) between the NSSM and PSSM groups. The proportion of N3 sleep was significantly higher in the PSSM group than in the NSSM group (14.94 ± 18.38% vs 6.42 ± 10.31%, P = .002). However, significant differences were not observed in the proportion of N1 (14.13 ± 7.10% vs 13.71 ± 11.44%, P = .745), N2 (51.24 ± 12.00% vs 48.31 ± 17.19%, P = .353), or REM sleep (18.86 ± 8.33% vs 17.96 ± 6.22%, P = .349) between the 2 groups.

Self-reported measures

The PSQI, ESS scores, BDI, and self-reported questionnaire data are shown in Table 2. ANCOVA (adjusted for age and sex) showed the NSSM group had a significantly higher PSQI score than the PSSM group (14.15 ± 3.54 vs 10.83 ± 4.20, P < .001). However, the BDI and ESS scores were not different between the 2 groups (16.75 ± 10.47 vs 16.40 ± 13.04, P = .792; 6.12 ± 4.69 vs 7.97 ± 4.83, P = .143, respectively). After adjusting for age and sex, all sleep questionnaire measures were significantly different between the 2 groups. Self-reported morning awakening was significantly more frequent in the NSSM group (3.65 ± 2.25 vs 2.89 ± 2.11, P = .038). Furthermore, the PSSM group felt significantly more refreshed after sleep (morning feeling; 2.32 ± 0.77 vs 2.06 ± 0.72, P = .029). The NSSM group had significantly longer self-reported SOL than the PSSM group (77.79 ± 86.42 vs 30.00 ± 19.06 minutes, P = .001). The SOL discrepancy was also significantly greater in the NSSM than PSSM group (59.50 ± 78.25 vs 11.44 ± 18.63 minutes, P = .001).

Table 2.

Clinical data of the NSSM and PSSM groups.

Variables Total (n = 150) NSSM (MI > 0, n = 115) PSSM (MI < 0, n = 35) P
PSQI score 13.37 ± 3.95 14.15 ± 3.54 10.83 ± 4.20 < .001
BDI 16.67 ± 11.08 16.75 ± 10.47 16.40 ± 13.04 .792
ESS score 6.54 ± 4.77 6.12 ± 4.69 7.97 ± 4.83 .143
Morning awakenings (n) 3.46 ± 2.23 3.65 ± 2.25 2.89 ± 2.11 .038
Morning feeling score 2.12 ± 0.74 2.06 ± 0.72 2.32 ± 0.77 .029
Self-reported SOL (min) 66.49 ± 78.67 77.79 ± 86.42 30.00 ± 19.06 .001
Self-reported TST (min) 303.16 ± 128.94 255.34 ± 103.86 460.29 ± 59.53 < .001
SOL discrepancy 48.14 ± 71.87 59.50 ± 78.25 11.44 ± 18.63 .001
TST discrepancy −95.92 ± 116.83 −140.00 ± 87.12 51.57 ± 71.85
Misperception index 0.24 ± 0.33 0.36 ± 0.24 −0.15 ± 0.28
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Data are from ANCOVA adjusted for age and sex. ANCOVA = analysis of covariance, BDI = Beck Depression Inventory, ESS = Epworth Sleepiness Scale, MI = misperception index, NSSM = negative sleep state misperception, PSQI = Pittsburgh Sleep Quality Index, PSSM = positive sleep state misperception, SOL = sleep-onset latency, TST = total sleep time.

Partial correlation of the MI with polysomnographic variables and self-reported measures

The partial correlations of the MI with the polysomnographic variables and self-reported measures are listed in Table 3 after controlling for age and sex. The MI was negatively correlated with N3 sleep (r = −.227, P = .005) based on nocturnal PSG, and positively correlated with PSQI (r = .311, P < .001), morning awakenings (r = .219, P = .01), self-reported SOL (r = .412, P < .001), and SOL discrepancy (r = .439, P < .001) across all participants.

Table 3.

Results of the partial correlation analysis of MI with polysomnographic variables and self-reported measures.

Variables N3 Sleep (%) PSQI BDI Morning Awakenings (n) Self-Reported SOL SOL Discrepancy
All (n = 150)
MI −0.227** 0.311** 0.083 0.219* 0.412** 0.439**
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*P < .05, **P < .01. BDI = Beck Depression Inventory, MI = misperception index, PSQI = Pittsburgh Sleep Quality Index, SOL = sleep-onset latency.

Multiple regression analysis

Multiple regression analysis was used to determine the variables associated with MI in all participants (Table 4). Significant variables in the partial correlation analysis (N3 sleep, PSQI, morning awakenings, self-reported SOL, and SOL discrepancy) were included. We selected the independent variables included in the multiple linear regression model considering their correlation with the dependent variable, their collinearity, and their clinical significance reported in other studies. Self-reported SOL and SOL discrepancy were subsequently omitted due to their similarity with MI. BDI was added to the regression model because depression was reported to influence sleep perception in several studies.28,29 Therefore, the independent variables in the multiple linear regression model were N3, PSQI, morning awakening, and BDI. The analysis showed that a low proportion of N3 sleep (P < .001), high PSQI score (P < .001), and more morning awakenings (P = .029) were significantly associated with the degree of MI.

Table 4.

Results of the multiple regression analyses: variables associated with the MI of all participants.

Dependent Variable Independent Variables B SE β t P
All (n = 150)
MI Constant −0.116 0.119 −0.974 .332
Age < 0.001 0.002 0.015 0.196 .845
Sex −0.028 0.048 −0.046 −0.596 .552
N3 sleep (%) −0.008 0.002 −0.309 −4.037 < .001
PSQI 0.025 0.007 0.320 3.767 < .001
BDI −0.001 0.002 −0.040 −0.476 .635
Morning awakenings 0.023 0.011 0.170 2.203 .029
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BDI = Beck Depression Inventory, MI = misperception index, PSQI = Pittsburgh Sleep Quality Index.

DISCUSSION

In the present study, clinical characteristics and polysomnographic variables were compared between NSSM and PSSM groups to identify factors affecting sleep perception in patients with insomnia. To the best of our knowledge, this is the first study in which PSSM and NSSM were compared within a cohort of patients with insomnia.

In the current study, slow-wave sleep was more prominent in the PSSM group. Other polysomnographic variables did not differ between the NSSM and PSSM groups, except for the proportion of N3 sleep. Furthermore, a low proportion of N3 sleep was associated with negative misperception of sleep duration in all patients, indicating that more N3 sleep is related to longer self-reported sleep duration. In previous PSG studies, the slow-wave sleep of insomnia patients with NSSM did not differ from normal controls or patients with “objective insomnia.”16,30 In a recent study, EEG changes in members of the general population who under- and overestimate sleep duration were investigated.31 Underestimators showed shorter-duration slow-wave sleep based on PSG, in agreement with our study.31 Increased EEG activation, in association with increased arousal, may reduce the amount of slow-wave sleep.31 This indicates that slow-wave sleep is associated with the perception of sufficient sleep duration. Long-duration slow-wave sleep was associated with more accurate sleep time estimates.32 Therefore, although several self-reported factors could affect sleep perception, clinicians should consider the possibility that patients with insomnia may underestimate their sleep duration due to slow-wave sleep (ie, the proportion of slow-wave sleep in insomnia patients may affect their perception of sleep duration).

The degree of misperception of sleep duration in our patients with insomnia was associated with self-reported sleep quality. The PSQI assesses self-reported sleep quality and disturbances in the past month.33 Because a high PSQI was associated with increased MI in our patients with insomnia, the discrepancy between self-measured sleep duration in the morning and sleep duration measured objectively using nocturnal PSG likely reflects self-reported sleep quality over the previous month. Perceived sleep in the morning could be associated with the usual quality of sleep of patients with insomnia. Depressed mood and sleep discrepancies reportedly affect each other.28,29 Thus, the BDI was included in our regression model. However, it exhibited no significant partial correlations, and no significant associations in the multiple regression analysis. This may be explained by reference to the inconsistent results of other studies of sleep discrepancies in depressed patients. In contrast to the known relationship of depression with underestimation of sleep duration, depressed patients overestimated their sleep duration in some studies.5,34 In addition, the small number of patients in our PSSM group may have lowered the statistical power of the analysis. Thus, further studies with more participants are needed to investigate the association between self-reported sleep perception and depression.

In the current study, self-reported SOL was associated with sleep perception; patients with PSSM had a shorter self-reported SOL and smaller SOL discrepancy than the NSSM patients. Patients with insomnia often overestimate their SOL.35 Although self-reported SOL cannot be completely independent of self-reported TST, the discrepancy between self-reported and objective SOL could be clinically meaningful because objective SOL showed no significant difference between the 2 groups in this study according to nocturnal PSG, contrary to the significantly longer self-reported SOL seen in the patients with insomnia who underestimated their sleep. Moreover, the more self-reported awakenings associated with negative sleep state misperception seen in this study are in agreement with a previous study, in which sleep fragmentation affected SOL discrepancy.36 In addition to frequent arousal, individuals with misperception of SOL showed a bias toward sleep-related cognitions and “pre-sleep worry” in another study; this may partly explain misperception of sleep duration.37 Thus, perception of SOL and TST should be considered when evaluating patients with insomnia.

The self-reported number of awakenings and tiredness in the morning is associated with perception of sleep quality. In the current study, patients with PSSM had fewer self-reported awakenings and felt more refreshed in the morning. The number of self-reported awakenings during the night was a good predictor of perceived sleep quality in a previous study, which supports our results.38 Self-reported sleep quality is usually indexed by tiredness upon waking and the number of awakenings, in both control patients and patients with insomnia.39 Perception of inadequate sleep in patients with insomnia can impair daytime functioning.40 Similarly, people with insomnia experienced worse self-reported cognitive functioning in several studies, albeit not based on objective measures,41,42 and tend to report that they are sleep deficient.8 The impaired cognition and daytime functioning of patients with insomnia may be attributed to neuropsychological deficits.

Our NSSM patients were older than those with PSSM. In a previous study, participants in a general population–based cohort who overestimated their self-reported TST were significantly older than those with normal estimates.31 In a study of patients undergoing PSG, sleep-disordered NSSM and PSSM patients were similar in age.18 The association of age with sleep state misperception has been inconsistent among studies.30,43 However, our findings are in agreement with others in which the sleep quality of older people was poorer when self-measured rather than objectively.44,45 Age-related sleep changes are evident regardless of whether the measurements are self-reported or objective46; further study is needed to explore the relevance of age to sleep state misperception.

Harvey and Tang35 suggested that the concept of misperception of sleep may contribute to trivialization of insomnia in the clinical setting. As discussed in this study, self-reported quality of sleep and tiredness is associated with misperception of sleep; addressing these misperceptions may improve the treatment outcomes of patients with insomnia. Clear guidelines for addressing sleep misperception do not exist, although some pharmacological and nonpharmacological treatments are used in practice.7 A cognitive approach would be beneficial for patients with insomnia to correct dysfunctional beliefs about sleep.35 Positive effects of cognitive behavioral therapy on reduction in misperception of sleep have been documented in several studies.47,48 Interventions targeting putative factors underlying sleep misperception, such as anxiety and selective attention, should be considered.35

The present study had several limitations. First, there was no control group and a relatively small number of participants. Although in most previous studies, normal or “objective insomnia” participants were compared with NSSM patients, NSSM and PSSM groups were compared in the present study. Studies with larger cohorts are needed. Second, nocturnal PSG was performed on only 1 night. We aimed to accurately quantify the degree of misperception by collecting self-reported measures immediately after the nocturnal PSG, from which the objective measures are derived. Studies conducted over several nights are needed to exclude the possibility of a “first-night effect.” In addition to studies conducting PSG over more nights, prospective studies should be performed controlling for exogenous factors affecting self-reported sleep perception. Third, the exact disease duration of the patients with insomnia could not be determined as their medical records were retrospectively collected. Although all of the participants met the Diagnostic and Statistical Manual of Mental Disorders, fifth edition diagnostic criteria for insomnia disorder, the association of the disease duration and the self-reported sleep perception could not be analyzed. It would be helpful for future studies to include such factors in their analysis. Fourth, the neurophysiological examination was limited. The putative mechanisms of self-reported sleep perception have been discussed in several studies. A relationship between SOL discrepancy and glucose metabolism in specific brain regions associated with conscious awareness was reported.49 In another study, increased insomnia-related activation of certain brain regions in patients with sleep state misperception was suggested to reflect heightened sensitivity and cognitive distortions.50 Furthermore, increased EEG activity during NREM sleep in “sleep underestimators” and decreased EEG activity during REM sleep in “sleep overestimators” were reported.31 The associations of these patient characteristics with positive and negative sleep misperception and pathological sleep neurophysiology should be investigated in future studies.

CONCLUSIONS

This study identified factors associated with sleep perception in patients with insomnia by comparing clinical characteristics and polysomnographic variables between NSSM and PSSM groups. Polysomnographic variables, such as the proportion of slow-wave sleep, and self-reported measures including self-reported SOL, usual self-reported sleep quality, morning awakenings, and feeling refreshed after sleep, were associated with perception of sleep. Objective and self-reported characteristics of patients with insomnia should be properly evaluated and managed, as they affect perception of sleep.

ACKNOWLEDGMENTS

The authors thank all participants of this study.

ABBREVIATIONS

ANCOVA,

analysis of covariance

BDI,

Beck Depression Inventory

EEG,

electroencephalogram

ESS,

Epworth Sleepiness Scale

MI,

misperception index

PSG,

polysomnography

PSQI,

Pittsburgh Sleep Quality Index

PSSM,

positive sleep state misperception

SOL,

sleep-onset latency

TST,

total sleep time

DISCLOSURE STATEMENT

All authors have seen and approved the manuscript. Work for this study was performed at the Department of Psychiatry and Center for Sleep and Chronobiology, Seoul National University, College of Medicine and Hospital. The authors report no conflicts of interest

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