Marijke C. M. Gordijn

Comparison of the Munich Chronotype Questionnaire with the Horne‐Östberg's Morningness‐Eveningness score

We report on results from an Internet survey of sleeping habits in a Dutch population using the Munich Chronotype Questionnaire (MCTQ), supplemented with the Horne‐Östberg Morningness‐Eveningness Questionnaire (MEQ). The MCTQ was completed by 5,055 responders, of which 2,481 also completed the MEQ. MEQ score correlated well with the MCTQ assessment of time of mid‐sleep on free days (MSF; r=− 0.73) and on workdays (MSW; r=− 0.61). MEQ was more strongly correlated with MSF (50% of sleep time) than with sleep onset (0%), rise time (100%), or with any other percentile (10 to 40, 60% to 90%) of sleep on free days. The study shows that chronotype (based on MSF as measured by the MCTQ) strongly correlates with morningness‐eveningness (as measured by the MEQ). However, the MCTQ collects additional detailed information on sleep‐wake behavior under natural conditions.

Delayed Circadian Rhythm in Adults with Attention-Deficit/Hyperactivity Disorder and Chronic Sleep-Onset Insomnia

BACKGROUND Previous studies suggest circadian rhythm disturbances in children with attention-deficit/hyperactivity disorder (ADHD) and sleep-onset insomnia (SOI). We investigate here sleep and rhythms in activity and melatonin in adults with ADHD. METHODS Sleep logs and actigraphy data were collected during 1 week in 40 adults with ADHD, of whom 31 reported SOI. Salivary melatonin levels were assessed during 1 night. Sleep measures, circadian activity variables, and dim light melatonin onset were compared between groups of ADHD adults with and without SOI and with matched healthy control subjects. RESULTS Compared with control subjects, both groups of ADHD adults had longer sleep-onset latency and lower sleep efficiency. Adults with ADHD and SOI showed a delayed start and end of their sleep period and a delayed melatonin onset compared with adults with ADHD without SOI (p = .006; p = .023; p = .02) and compared with healthy control subjects (p = .014; p = .019; p = .000). Adults with ADHD and SOI also showed an attenuated 24-hour amplitude in their rest-activity pattern, in contrast to those without SOI, who showed a higher day-to-day stability. CONCLUSIONS These findings demonstrate diurnal rhythm deviations during everyday life in the majority of adults with ADHD that have SOI and suggest that potential benefits of rhythm-improving measures should be evaluated.

Can light make us bright? : Effects of light on cognition and sleep

Light elicits robust nonvisual effects on numerous physiological and behavioral variables, such as the human sleep-wake cycle and cognitive performance. Light effects crucially rely on properties such as dose, duration, timing, and wavelength. Recently, the use of methods such as fMRI to assess light effects on nonvisual brain responses has revealed how light can optimize brain function during specific cognitive tasks, especially in tasks of sustained attention. In this chapter, we address two main issues: how light impinges on cognition via consolidation of human sleep-wake cycles; and how light directly impacts on sleep and cognition, in particular in tasks of sustained attention. A thorough understanding of how light affects sleep and cognitive performance may help to improve light settings at home and at the workplace in order to improve well-being.

Circadian control of the sleep–wake cycle

It is beyond doubt that the timing of sleep is under control of the circadian pacemaker. Humans are a diurnal species; they sleep mostly at night, and they do so at approximately 24-h intervals. If they do not adhere to this general pattern, for instance when working night shifts or when travelling across time zones, they experience the stubborn influence of their circadian clock. In recent years much has been discovered about the organisation of the circadian clock. New photoreceptor cells in the retina have been found to influence the input to the clock, and much of the molecular machinery of the clock has been unravelled. It is now known that the circadian rhythm of sleep and wakefulness is only loosely coupled to the circadian rhythm of the pacemaker. New theories have been proposed for the functions of sleep and the sites at which those functions are executed. In spite of this rapid increase in knowledge of the circadian clock and of sleep regulatory processes, much remains to be discovered concerning the precise interaction between the biological clock and sleep timing. This is particularly unfortunate in view of the 24-h demands of our society for 7 days a week. Too little is known about the negative consequences of the societal pressures on well-being and performance.

Weak relationships between suppression of melatonin and suppression of sleepiness/fatigue in response to light exposure

In this paper we examine the relationship between melatonin suppression and reduction of sleepiness through light by comparing three different data sets. In total 36 subjects participated in three studies and received 4 h of bright light either from midnight till 4:00 hours (experiments A and B) or from noon till 16:00 hours (experiment C). In experiment A (night‐time light, partial illumination of the retina, pupil dilated) subjects were exposed to either 100 lx of ocular light on the temporal, 100 lx on the nasal part of the retina, or <10 lx of dim light on the whole retina. In experiments B (night‐time light, whole retina, pupil not dilated) and C (daytime light, whole retina, pupil not dilated) subjects were exposed either to bright (5000 lx) or to dim light (<10 lx). Subjective sleepiness/fatigue and melatonin concentrations in saliva were assessed hourly in all three experiments. For experiment A, a significant suppression of melatonin due to nasal and temporal illumination of the retina was found, that was not accompanied by a detectable reduction of subjective sleepiness/fatigue. For experiment B we found a suppression of melatonin that was paralleled with a significant reduction in subjective sleepiness, but not in fatigue. During experiment C we found no melatonin suppression but a reduction of subjective sleepiness, but also no effect on fatigue. From these data we conclude that the effects of light on sleepiness/fatigue are not mediated by melatonin and that the influence of endogenous melatonin concentration on sleepiness/fatigue is restricted.

Acute and Phase-Shifting Effects of Ocular and Extraocular Light in Human Circadian Physiology:

Light can influence physiology and performance of humans in two distinct ways. It can acutely change the level of physiological and behavioral parameters, and it can induce a phase shift in the circadian oscillators underlying variations in these levels. Until recently, both effects were thought to require retinal light perception. This view was challenged by Campbell and Murphy, who showed significant phase shifts in core body temperature and melatonin using an extraocular stimulus. Their study employed popliteal skin illumination and exclusively considered phase-shifting effects. In this paper, the authors explore both acute effects and phase-shifting effects of ocular as well as extraocular light. Twelve healthy males participated in a within-subject design and received all of three light conditions—(1) dim ocular light/no light to the knee, (2) dim ocular light/bright extraocular light to the knee, and (3) bright ocular light/no light to the knee—on separate nights in random order. The protocol consisted of an adaptation night followed by a 26-h period of sustained wakefulness, during which a 4-h light pulse was presented at a time when maximal phase delays were expected. The authors found neither immediate nor phase-shifting effects of extraocular light exposure on melatonin, core body temperature (CBT), or sleepiness. Ocular bright-light exposure reduced the nocturnal circadian drop in CBT, suppressed melatonin, and reduced sleepiness significantly. In addition, the 4-h ocular light pulse delayed the CBT rhythm by -55 min compared to the drift of the CBT rhythm in dim light. The melatonin rhythm shifted by -113 min, which differed significantly from the drift in the melatonin rhythm in the dim-light condition (-26 min). The failure to find immediate or phase-shifting effects in response to extraocular light in a within-subjects design in which effects of ocular bright light are confirmed strengthens the doubts raised by other labs of the impact of extraocular light on the human circadian system.

HUMAN SLEEP AND COGNITION, PT II: CLINICAL AND APPLIED RESEARCH

Light elicits robust nonvisual effects on numerous physiological and behavioral variables, such as the human sleep-wake cycle and cognitive performance. Light effects crucially rely on properties such as dose, duration, timing, and wavelength. Recently, the use of methods such as fMRI to assess light effects on nonvisual brain responses has revealed how light can optimize brain function during specific cognitive tasks, especially in tasks of sustained attention. In this chapter, we address two main issues: how light impinges on cognition via consolidation of human sleep-wake cycles; and how light directly impacts on sleep and cognition, in particular in tasks of sustained attention. A thorough understanding of how light affects sleep and cognitive performance may help to improve light settings at home and at the workplace in order to improve well-being.

Factors That Influence Standard Automated Perimetry Test Results in Glaucoma: Test Reliability, Technician Experience, Time of Day, and Season

PURPOSE To determine the influence of several factors on standard automated perimetry test results in glaucoma. METHODS Longitudinal Humphrey field analyzer 30-2 Swedish interactive threshold algorithm data from 160 eyes of 160 glaucoma patients were used. The influence of technician experience, time of day, and season on the mean deviation (MD) was determined by performing linear regression analysis of MD against time on a series of visual fields and subsequently performing a multiple linear regression analysis with the MD residuals as dependent variable and the factors mentioned above as independent variables. Analyses were performed with and without adjustment for the test reliability (fixation losses and false-positive and false-negative answers) and with and without stratification according to disease stage (baseline MD). RESULTS Mean follow-up was 9.4 years, with on average 10.8 tests per patient. Technician experience, time of day, and season were associated with the MD. Approximately 0.2 dB lower MD values were found for inexperienced technicians (P < 0.001), tests performed after lunch (P < 0.001), and tests performed in the summer or autumn (P < 0.001). The effects of time of day and season appeared to depend on disease stage. Independent of these effects, the percentage of false-positive answers strongly influenced the MD with a 1 dB increase in MD per 10% increase in false-positive answers. CONCLUSIONS Technician experience, time of day, season, and the percentage of false-positive answers have a significant influence on the MD of standard automated perimetry.

CHRONOTYPES AND SUBJECTIVE SLEEP PARAMETERS IN EPILEPSY PATIENTS: A LARGE QUESTIONNAIRE STUDY

Accumulating evidence suggests epilepsy and seizures may influence circadian rhythms and that circadian rhythms may influence epilepsy. It is also conceivable that seizure timing influences the timing of daily activities, sleeping, and wakefulness (i.e., chronotype). Only one group has studied the distribution of chronotypes of epileptics, showing significant differences between the diurnal activity patterns in two groups of patients with different epilepsy syndromes. The authors performed a questionnaire-based study of 200 epilepsy patients to compare the distribution of chronotypes and subjective sleep parameters of sleep duration and time of mid-sleep on free days to the distribution in the general population (n = 4042). Within this large group of epilepsy patients, we also compared the chronotypes of subsamples with well-defined epilepsy syndromes, i.e., temporal lobe epilepsy [TLE; n = 46], frontal lobe epilepsy [FLE; n = 30], and juvenile myoclonic epilepsy [JME; n = 38]. In addition, 27 patients who had had surgery for TLE were compared with those with TLE who had not had surgery. Both the Morningness-Eveningness Questionnaire and Munich Chronotype Questionnaire were used to determine chronotypes and subjective sleep parameters. Significant differences in morningness/eveningness distribution, timing of mid-sleep (corrected for sleep duration), and total sleep time on free days were found between epileptics and healthy controls. Those with epilepsy were more morning oriented, had earlier mid-sleep on free days, and longer sleep duration on free days (p < .001). However, distributions of chronotypes and sleep parameters between the groups of people with TLE, FLE, and JME did not differ. Persons who had surgery for TLE had similar morningness-eveningness parameters and similar sleep durations compared to those without surgery, but mid-sleep on free days was earlier in operated patients (p = .039). In conclusion, this is the first large study focusing on chronotypes in people with epilepsy. We show that the distribution of chronotypes and subjective sleep parameters of epileptics, in general, is different from that of healthy controls. Nevertheless, no differences are observed between patients with specified epilepsy syndromes, although they exhibit seizures with different diurnal patterns. Our results suggest that epilepsy, itself, rather than seizure timing, has a significant influence on chronotype behavior and subjective sleep parameters. (Author correspondence: w.hofstra@mst.nl)

Effects of artificial dawn on sleep inertia, skin temperature, and the awakening cortisol response

The effect of artificial dawn during the last 30 min of sleep on subsequent dissipation of sleep inertia was investigated, including possible involvement of cortisol and thermoregulatory processes. Sixteen healthy subjects who reported difficulty with waking up participated in random order in a control and an artificial dawn night. Sleep inertia severity was measured by subjective ratings of sleepiness and activation, and by performance on an addition and a reaction time task measured at 1, 15, 30, 45, 60, and 90 min after waking up at habitual wake up time at workdays. At all intervals, saliva samples were collected for cortisol analysis. Sleep electroencephalogram was recorded during the 30 min prior to waking up; core body temperature and skin temperatures were recorded continuously until 90 min after waking up. Subjective sleepiness was significantly decreased and subjective activation increased after waking up in the artificial dawn condition as compared with control, in which lights were turned on at waking up. These effects can be explained by effects of artificial dawn on skin temperature and amount of wakefulness during the 30 min prior to the alarm. Artificial dawn accelerated the decline in skin temperature and in the distal‐to‐proximal skin temperature gradient after getting up. No significant effects of artificial dawn on performance, core body temperature, and cortisol were found. These results suggest that the physiology underlying the positive effects of artificial dawn on the dissipation of sleep inertia involves light sleep and an accelerated skin temperature decline after awakening.