A new study conducted by researchers at Washington State University shows that individuals with chronic sleep-onset insomnia who pulled an all-nighter performed up to twice as bad on a reaction time task as healthy normal sleepers.
Their findings were published today in the online journal Nature and Science of Sleep.
Poor daytime functioning is a frequent complaint among those suffering from insomnia, said lead author Devon Hansen, an assistant professor in the Elson S. Floyd College of Medicine and a researcher in the WSU Sleep and Performance Research Center.
However, previous studies have found that their daytime cognitive performance is not significantly degraded, seemingly suggesting that it is a perceived issue that does not reflect a real impairment.
The WSU study of individuals with sleep-onset insomnia revealed that the impairment may in fact be real but hidden during the normal day–yet exposed after pulling an all-nighter, which impacted them much more than age-matched control subjects.
The finding caught the WSU research team by surprise.
“There has been a theory about what perpetuates insomnia that focuses on hyperarousal, an activation in their system that keeps those with insomnia from being able to wind down when they go to bed,” Hansen said.
“We thought that this hyperarousal would protect them to some extent and had hypothesized that their performance after a night of total sleep deprivation would be better than normal healthy sleepers. Instead, we found the exact opposite.”
Hansen, who in a previous career worked as a therapist in a sleep clinic, said the study adds credibility to insomnia patients’ experiences.
She also said it serves as a warning to poor sleepers that they should try to maintain a regular sleep schedule and avoid pushing their limits by staying up all night.
The research team studied 14 volunteer participants. Half of the group consisted of individuals who had chronic sleep-onset insomnia, the inability to fall asleep within 30 minutes for at least three nights a week for more than three months.
The other half were healthy normal sleepers who served as controls. The two groups of participants were matched in age, with all participants aged between 22 and 40 and an average age of 29 for both groups.
Participants spent a total of five days and four nights in the sleep laboratory. They were allowed to sleep normally during the first two nights.
They were kept awake the next night and following day–totaling 38 hours of total sleep deprivation–followed by a night of recovery sleep.
During their time awake, participants completed a series of performance tasks every three hours.
This included a widely used alertness test known as the psychomotor vigilance test (PVT), which measures participants’ response times to visual stimuli that appear on a screen at random intervals.
The researchers analyzed PVT data for lapses of attention (i.e., slow reaction times) and false starts (i.e., responses that occur before the stimulus appears), comparing the findings between the two groups both before and during sleep deprivation.
Before sleep deprivation, the insomnia group’s performance on the PVT looked very similar to that of the control group. However, as soon as sleep deprivation started the researchers began to see a dramatic increase in lapses of attention and false starts in the insomnia group. At one point during the night, their performance was twice as bad as that of the healthy normal sleepers.
At one point during the night, their performance was twice as bad as that of the healthy normal sleepers.
“Our study suggests that even with a few hours of sleep deprivation–which people routinely experience for work or family reasons–those with sleep-onset insomnia may be much more impaired than those who normally sleep well at night,” Hansen said.
“This may increase their risk of errors and accidents whenever time-sensitive performance is required, such as while driving or when focused on a safety-critical task.”
Hansen cautioned that since their study looked specifically at individuals with sleep-onset insomnia, their findings may not hold up in other insomnia subtypes, such as sleep-maintenance insomnia–which is characterized by difficulty staying asleep–and terminal insomnia–which involves early-morning awakenings. She plans to repeat the study in those groups to find out.
Funding: Funding support for this study came from the Office of Naval Research through Pulsar Informatics, LLC.
Delayed sleep–wake phase disorder (DSWPD) is a circadian rhythm sleep–wake disorder where the sleep–wake rhythm is significantly delayed in relation to external demands, resulting in inability to fall asleep and difficulty awakening at socially acceptable times (American Academy of Sleep Medicine, 2014).
The sleep–wake phase delay generally reflects a delay in the circadian time keeping system (American Academy of Sleep Medicine, 2014), possibly due to abnormal circadian processes [e.g., particularly long intrinsic circadian periods and/or altered light sensitivity (Aoki et al., 2001; Campbell and Murphy, 2007; Micic et al., 2013; Watson et al., 2018)], abnormal homeostatic processes [e.g., slow homeostatic accumulation of sleep drive (Uchiyama et al., 1999, 2000)], or abnormal interactions between these two processes (American Academy of Sleep Medicine, 2014).
Also environmental, social, and behavioral factors are involved in sleep regulation and likely play important roles in the development and maintenance of the disorder [e.g., inadequate light exposure or timing of light exposure, irregular work schedules, family dysfunction, and poor sleep habits (Kalak et al., 2012; American Academy of Sleep Medicine, 2014; Micic et al., 2016)]. When allowed to sleep at preferred times, sleep in individuals with DSWPD is essentially normal for age (Saxvig et al., 2013; American Academy of Sleep Medicine, 2014) possibly with the exception of sleep onset latency (SOL) which appears to be prolonged even on self-chosen sleep schedules (Watanabe et al., 2003; Saxvig et al., 2013).
Some researchers have suggested that cognitive processes usually associated with sleep onset insomnia (e.g., worry, conditioning) may be involved in DSWPD (Lack and Wright, 2007; Gradisar and Crowley, 2013; Richardson et al., 2016). Finally, it has been shown that cognitive-emotional processes may affect physiological sleep processes (Born et al., 1999), and it is possible that such factors may contribute to the development of DSWPD.
Most people, also those without DSWPD, have intrinsic periods slightly longer than the 24 h light/dark cycle (Czeisler et al., 1999; Herman, 2011) and hence have a tendency to delay their sleep/wake pattern in absence of proper zeitgeber exposure (e.g., during weekends). On weekdays, however, they may be required to rise early due to external demands, producing a discrepancy between weekend and weekday sleep in terms of timing and duration. This discrepancy is referred to as a social jetlag, often operationalized as the difference between midsleep on weekdays and free days (Wittmann et al., 2006).
Most individuals with DSWPD are extreme evening types (Abe et al., 2011) and in general, evening types have larger social jetlag than morning or intermediate types (Wittmann et al., 2006). To our knowledge, only one previous study has investigated social jetlag in individuals with DSWPD, but that study did not include a control group of normal sleepers (Kayaba et al., 2018).
A large misalignment between the delayed intrinsic rhythm and external demands can make it hard for individuals with DSWPD to comply with commonly accepted time schedules, which ultimately may result in school/work non-attendance rather than social jetlag. On that account, Mongrain et al. (2004) have suggested that whereas evening persons often will try to adhere to socially accepted demands, individuals with DSWPD may more often have “given up” and therefore to a larger degree sleep at their preferred time.
According to such notions, the degree of social jetlag would be a distinguishing factor between eveningness and DSWPD. Hence, further exploration of the habitual sleep patterns in individuals with DSWPD with a particular focus on social jetlag is warranted.
Epidemiological studies indicate that symptoms consistent with DSWPD are associated with poor academic performance, non-attendance at school, poor health behaviors, and mental health problems (Saxvig et al., 2012; Sivertsen et al., 2013, 2015a,b). These associations may in part reflect characteristics inherent to individuals with DSWPD [e.g., personality traits (Wilhelmsen-Langeland et al., 2014; Micic et al., 2017)], psychosocial consequences of being out of sync with society [e.g., heightened conflict levels in school or at home (Wilhelmsen-Langeland et al., 2012)], or cognitive-emotional processes associated with DSWPD [e.g., worry, rumination (Richardson et al., 2019)].
In addition, the physiological consequences of social jetlag may affect daytime functioning and mental health in a negative manner. Social jetlag implies chronic weekday sleep curtailment, which causes sleepiness as well as impaired physiological and neurobehavioral functioning (Van Dongen et al., 2003; Banks and Dinges, 2007).
Moreover, due to the synchrony effect (circadian variations in performance and alertness), early work/school hours appear to be sub-optimal for performance in late chronotypes, who tend to perform better later in the day compared to earlier chronotypes (Carrier and Monk, 2000; Goldstein et al., 2007). Few studies have investigated such time of day variations in performance in individuals with DSWPD by objectively measuring performance at different times of day in experimental, controlled settings. In a recent study, Solheim et al. (2018) showed impaired morning performance on a sustained reaction time task in individuals with DSWPD, particularly following forced awakenings.
However, since the participants in that study were tested immediately after awakening, the authors attributed the findings to sleep inertia, a transient period of confusion and reduced alertness following forced awakenings (Tassi and Muzet, 2000), rather than to the synchrony effect or effects of sleep curtailment. Sleep inertia is usually of short duration, although in some cases it has been reported to last for a few hours; among others depending on prior sleep history, time of day, and the sleep stage awaken from (Tassi and Muzet, 2000).
Complimentary studies where performance is investigated a few hours after awakening to eliminate the effects of sleep inertia should thus be performed to further elucidate possible impairments in daytime performance in individuals with DSWPD.
The aim of the present study was to explore habitual sleep as well as social jetlag and day-to-day variations in sleep in youths with DSWPD, compared to healthy controls, by means of sleep diaries and actigraphy monitoring. We also aimed to investigate evening and morning performance in participants with DSWPD compared to controls, by means of a simple, sustained reaction time task.
We hypothesized that
(H1): Participants with DSWPD have later sleep timing than controls. Moreover, since all recruited participants attended school/work, and hence, adhered to social requirements, we hypothesized that
(H2): Participants with DSWPD have a larger social jetlag, shorter weekday sleep, longer weekend sleep, and more day-to-day variation in sleep than controls.
Based on previous research we expected that
(H3): Participants with DSWPD have longer SOL, particularly on weekdays, but otherwise similar sleep as controls.
We also hypothesized that
(H4): Participants with DSWPD perform better (faster with fewer lapses) when sustained reaction is measured in the evening than when measured in the morning, whereas controls perform better in the morning than in the evening.
Discussion
In accordance with the diagnostic criteria for DSWPD (American Academy of Sleep Medicine, 2014), and in support of hypothesis H1, results from the sleep diaries showed later sleep timing in the DSWPD group compared to the control group. Both groups slept later during weekends compared to weekdays, but there were no differences between the groups in terms of weekday vs. weekend sleep (no interaction effect), no difference in social jetlag, and no difference in ISD with respect to sleep timing, refuting hypothesis H2. Hypothesis H3 was also contradicted, as the DSWPD group reported longer SOL, poorer SE, and poorer daytime functioning than the control group both on weekdays and during weekends. Moreover, the DSWPD group had higher ISD in SOL, TST, and SE than the control group.
The groups had similar performances on the evening administration of the RTT, whereas the control group performed clearly better (faster with fewer lapses) than the DSWPD group on the morning administration of the test (interaction effect), lending support to hypothesis H4.
To our knowledge, no previous study has addressed social jetlag in individuals with DSWPD compared to a control group of normal sleepers. Previous studies have shown that late chronotypes have larger social jetlag than early or intermediate chronotypes (Wittmann et al., 2006). Given the association between DSWPD and eveningness it was reasonable to assume a large social jetlag also in youths with DSWPD.
However, Mongrain et al. (2004) have suggested that external constraints may affect the sleep habits of evening types more than individuals with DSWPD, since the former group is expected to be better able to adhere to accepted social demands than the latter group. In the present study, all participants had daytime obligations in that all but one (who was employed) attended high school, college, or university. The DSWPD group still had rise time as late as 10:31 on weekdays.
Schedules in Norwegian colleges and universities tend to vary and are often flexible. Since most of the participants in the present study were college/university students (57.5% in the DSWPD group and 81.0% in the control group) it is likely that flexible school schedules allowed them to minimize social jetlag and yet adhere to school obligations.
Since the degree of social jetlag is largely dependent on the time schedule of social obligations, we expect that the degree of social jetlag may be different in different populations of individuals with DSWPD. In the present study, we did not demonstrate differences in social jetlag between high school students and college/university students with DSWPD.
Previous studies have indicated that individuals with DSWPD generally have more irregular sleep patterns than normal sleepers (Gradisar et al., 2011) which also is in line with our clinical impression. A patient with DSWPD may typically manage to rise early one morning, oversleep by several hours the next morning, and then spend the next night fully awake. Hence, we considered it plausible that sleep patterns in students with DSWPD would be characterized by large day-to-day variations in sleep (i.e., higher ISD), depending on daily obligations and prior night sleep durations, rather than the weekday–weekend discrepancy usually characterizing a social jetlag.
On such grounds, we compared the 7-day ISD (Sanchez-Ortuno and Edinger, 2012; Bei et al., 2016) for the sleep diary parameters bedtime, rise time, SOL, TST, and SE (Sanchez-Ortuno and Edinger, 2012). Results showed that the ISD in sleep timing actually was similar in the two groups. However, the sleep diary data revealed larger ISD in SOL, TST, and SE in the DSWPD group than in the control group.
Compared to bedtime and rise time, SOL, TST, and SE are to a lesser degree will-controlled. Hence, it may seem that the participants with DSWPD managed to adhere to a relatively regular (yet late) sleep schedule, but at the cost of sleep quality.
Sleep duration did not differ between the groups. However, the DSWPD group reported longer SOL, poorer SE, poorer sleep quality, and poorer daytime functioning than controls both on weekdays and during weekends. The SOL week average was 44 min in the DSWPD group, which is substantially longer than the ≤30 min that is considered normal (American Academy of Sleep Medicine, 2014). The finding of longer SOL in individuals with DSWPD is in line with previous studies (Campbell and Murphy, 2007; Saxvig et al., 2013; Watanabe et al., 2003), and has commonly been attributed to attempts to fall asleep at circadian phases not optimal for sleep initiation (American Academy of Sleep Medicine, 2014).
It has been suggested that individuals with DSWPD may make an effort to adhere to socially acceptable sleep schedules even on free days (de Souza and Hidalgo, 2014), explaining the finding of prolonged SOL also during weekends. Another possibility, which has been advocated by for example Lack and Wright (2007), is that individuals with DSWPD may develop conditioned sleep onset insomnia due to numerous experiences of unsuccessful attempts to fall asleep in the evening.
A previous study has shown that similar to individuals with insomnia, individuals with DSWPD display an attentional bias for sleep-related stimuli (Marchetti et al., 2006), providing evidence that psychological mechanisms may play a role in the development and/or maintenance of DSWPD. This notion was recently reviewed and supported by Richardson et al. (2016, 2019). SE was approximately 85% in the DSWPD group, which is in the lower end of what is considered normal (≥85%) (American Academy of Sleep Medicine, 2014).
Poorer SE normally reflects more wake time during the night which may lead to poorer ratings of sleep quality, which may explain why the participants with DSWPD rated their sleep quality and daytime functioning poorer than did the healthy controls, despite similar sleep durations.
Lower ratings of sleep quality and daytime functioning may also result from reporting bias, either in relation to psychological mechanisms found in insomnia or in relation to circadian variations in alertness. Evening chronotypes tend to feel sleepy in the morning and may thus be more likely to report dissatisfaction with sleep and daytime functioning when completing the sleep diary at that time, which would be in line with the instructions.
The fact that the actigraphy recordings did not show group differences in SOL, TST, and SE seems to support the notion of a reporting bias influencing the sleep diary data.
However, although actigraphy is a recommended method for measuring sleep patterns over time (Ancoli-Israel et al., 2003; Morgenthaler et al., 2007) with high sensitivity (ability to identify sleep as sleep) and accuracy (ability to correctly identify the right state), actigraphy monitoring has low specificity (ability to identify wake as wake) (Marino et al., 2013). Hence, measures of wake TIB (e.g., SOL) obtained by actigraphy monitoring should be interpreted with caution.
Results from the RTT showed similar group performances in the evening. However, whereas the controls performed better (faster with fewer lapses) in the morning, the DSWPD group performed poorer. The fact that the morning RTT was administered several hours after awakening (rise time at 07:00 h, testing at 10:00 h), suggests that the poor morning performance in the participants with DSWPD was not merely a transient effect of sleep inertia as has been suggested by Solheim et al. (2018).
These performance decrements are thus likely to be present throughout a school or workday of individuals with DSWPD, significantly affecting their daytime functioning. These results support the presence of a synchrony effect in individuals with DSWPD, with optimal performance at a late time of day.
It is, however, plausible that sleep curtailment on the night between the test sessions significantly affected morning performance in the DSWPD group. Sleep duration was not recorded on this particular night, but PSG recordings from the previous night [data published elsewhere (Saxvig et al., 2013)] show a SP from 00:07 to 08:55 in the control group and from 03:08 to 12:44 in the DSWPD group. Hence, it is probably safe to assume that participants in the DSWPD group obtained less sleep than the control group before the required rise time at 07:00 h.
The design of the present study does not allow for a distinction between the effects of sleep curtailment and the synchrony effect. However, we argue that the results importantly illustrate the likely performance decrements individuals with DSWPD experience when trying to adhere to early morning obligations, such as school or work.
Strengths and Limitations
An asset of the present study was that sleep was recorded both subjectively and objectively using validated instruments, and reaction time was measured using a validated objective test. Another strength relates to the timing of the morning reaction time testing (3 h after rise time), which eliminated confounding effects of sleep inertia.
Being part of a larger clinical trial, inclusion criteria in the study were strict and all participants were thoroughly diagnosed and screened for comorbidity, yielding a rather homogenous group with respect to age and occupation (young students). DSWPD is assumed to be especially common in this particular population (Saxvig et al., 2012; Lovato et al., 2013; Sivertsen et al., 2013); hence, findings in the present study are likely highly illustrative for many youths with DSWPD.
Likewise, it should be noted that the findings may not be representative for other populations of DSWPD, in particular since social jetlag reflects the impact of social obligations on sleep, and since the nature of social obligations may vary depending on age and occupation. Hence, future studies should address social jetlag also in other populations of DSPWD. In the present study, we did not have in depth information about the physical and social environment of each participant (e.g., school schedules). Since social jetlag reflects the interaction between internal (physiological and psychological) and external (physical and social) factors, it seems important to address such factors in future studies on social jetlag in DSWPD.
The present study has some limitations with respect to the RTT protocol. With only two assessments points for performance it was not possible to assess curvilinear time of day effects. Moreover, there was no temporal relationship between the sleep diary/actigraphy recording and the reaction time testing; hence, it is not possible to know whether the morning decrements in performance in the DSWPD group was related to the synchrony effect or to sleep curtailment.
Another limitation related to the protocol was the use of light blocking sunglasses prior to reaction time testing. Both groups followed the same protocol and wore sunglasses at the same time of day, still it is possible that the groups were differentially affected by this procedure. The effect of light depends on the time of exposure in relation to the endogenous circadian rhythm, and since DSWPD is usually characterized by a circadian delay (Chang et al., 2009; Micic et al., 2013, 2016; Saxvig et al., 2013), the groups may have worn sunglasses at different circadian times. Moreover, some studies suggest that individuals with DSWPD may have altered sensitivity to light (Aoki et al., 2001; Watson et al., 2018).
Finally, due to a high level of dependency between the variables we did not control for the number of analyses conducted in the present study, as it would greatly have reduced power and increased the risk for type 1 errors. However, the risk for type 2 errors should be kept in mind when interpreting the results.
It should also be noted that the sample size in the present study was relatively small, in particular the control group, hence some of the within-group sub-analyses may have been be slightly underpowered (e.g., comparing social jetlag between high school students and college/university students within the DSWPD group, and comparing evening and morning performance on the RTT within the control group).
Conclusion
In conclusion, participants with DSWPD had later timing of sleep compared to controls, but sleep duration, the degree of social jetlag, and ISD in sleep timing did not differ between the groups.
The participants with DSWPD generally reported longer SOL, poorer SE, poorer sleep quality, and poorer daytime functioning than the controls, despite similar sleep durations, and they had larger ISD in SOL, sleep duration, and SE. Hence, youths with DSWPD may be able to maintain a regular (yet late) sleep schedule, but subjective sleep may be of poorer and more variable quality compared to normal sleepers.
Reaction time performance in the DSWPD group was poorer (slower with more lapses) in the morning than in the evening, whereas the control group performed better (faster with fewer lapses) in the morning than in the evening. The poor morning performance in the DSWPD group in relation to the controls likely represents the combined impact of sleep curtailment and the synchrony effect, and importantly illustrates the challenges youths with DSWPD face when trying to adhere to early morning obligations.
Source:
Washington State University
Media Contacts:
Devon Hansen – Washington State University
Image Source:
The image is in the public domain.
Original Research: Closed access
“Psychomotor Vigilance Impairment During Total Sleep Deprivation Is Exacerbated in Sleep-Onset Insomnia”. Hansen DA, Layton ME, Riedy SM, Van Dongen HPA.
Nature and Science of Sleep doi:10.2147/NSS.S224641.
