Gerard A. Kerkhof

University of Amsterdam | UVA · Department of Psychology

Background The efficacy of virtual reality exposure therapy (VRET) for fear of flying has been well established. Yet, little is known about the extent to which anxiety sensitivity and self-efficacy predict the efficacy of VRET. We aimed at investigating these cognitive predictors as well as the contribution of the therapeutic alliance to treatment...

Network theory, as a theoretical and methodological framework, is energizing many research fields, among which clinical psychology and psychiatry. Fundamental to the network theory of psychopathology is the role of specific symptoms and their interactions. Current statistical tools, however, fail to fully capture this constitutional property. We pr...

Network theory, as a theoretical and methodological framework, is energizing many research fields, among which clinical psychology and psychiatry. Fundamental to the network theory of psychopathology is the role of specific symptoms and their interactions. Current statistical tools, however, fail to fully capture this constitutional property. We pr...

Network theory, as a theoretical and methodological framework, is energizing many research fields, among which clinical psychology and psychiatry. Fundamental to the network theory of psychopathology is the role of specific symptoms and their interactions. Current statistical tools, however, fail to fully capture this constitutional property. We pr...

Taking into consideration that shift work has a wide-ranging impact on circadian and sleep functioning, it seems likely that shift work increases the risk of a general sleep disturbance, spread out over a multitude of comorbid sleep disorders. The aim of the present study is to analyze and present the sleep disorder data of 250 shift workers and 97...

Objective: There is a surging public interest in The Netherlands concerning sleep, sleep disorders and associated health. For a proper perspective, it is necessary to have reliable information on the prevalence of sleep characteristics at the national level. This study set out to assess prevalence rates and key characteristics of sleep and sleep d...

The aim of this longitudinal study on novice police officers was to investigate inter-individual differences in sleep response to shift work, and to identify potential baseline predictors thereof. A total of 42 subjects were assessed at baseline, prior to commencing shift work. They were re-assessed during three follow-up sessions within the first...

Cortisol acts as a critical biological intermediary through which chronic stressors like shift work impact upon multiple physiological, neuro-endocrine and hormonal functions. Therefore, the cortisol awakening response (CAR) is suggested as a prime index of shift work tolerance. Repeated assessments of the CAR (calculated as MnInc) in a group of 25...

The aim of this study was to examine how subjective shift work tolerance was related to general health variables, with the expectation of inter-individual differences in the nature of this relation. A total of 740 employees of the Dutch Police force completed a questionnaire, covering seven health-related domains: sleep quality, sleep duration, nee...

A majority of visually impaired individuals (VIP's) reports severe complaints of daytime fatigue and sleepiness. Both VIP's and caregivers frame these complaints as caused by compensatory effort needed to fulfil daytime activities in the (partial) absence of vision. An alternative explanation for this complaint could be the presence of a sleep diso...

Sleep reduction, resulting from insufficient or poor sleep, is a common phenomenon in adolescents. Due to its severe negative psychological and behavioral daytime consequences, it is important to have a reliable and valid measure to assess symptoms of sleep reduction. This study aims to validate the Sleep Reduction Screening Questionnaire (SRSQ) th...

Most individuals with mental disorders complain about the problems they experience with sleeping and waking. It is becoming evident that careful diagnosis of sleep-wake disorders is of great importance for the prevention and treatment of mental disorders. Since the introduction of the DSM-IV, clinical scientific research has provided important new...

Background: A number of studies have demonstrated the efficacy of virtual reality exposure therapy (VRET) in specific phobias, but research in seriously impaired patients with agoraphobia is lacking. In this randomized controlled trial with patients with agoraphobia and panic disorder, VRET and exposure in vivo were compared in terms of outcome an...

During sessions at 4 a.m., 10 a.m., 4 p.m., and 10 p.m., measurements were taken of the auditory AEP following the onset of a burst of white noise. For all subjects, a significant time-of-day fluctuation of the N105-P194 amplitude was found. The time of day at which the maximal value was recorded, however, appeared to vary with the subject’s score...

Een chronische slaapstoornis draagt bij aan het ontstaan of voortbestaan van vele ziekten, zoals stemmings- en angststoornissen, hart- en vaatziekten en aandoeningen van het immuunsysteem. Bijvoorbeeld chronische slapeloosheid (insomnia) op jonge leeftijd leidt tot een verhoogd risico op depressie en andere psychiatrische ziekten. Voorafgaande aan...

The primary objectives of this study were to construct a self-assessment questionnaire for sleep disorders based on the International Classification of Sleep Disorders-2, and to evaluate the questionnaire's psychometric properties with respect to its total score and the individual scores for each of the six sleep disorders. In total, 1269 patients,...

This prospective quasi-experiment (N = 175; mean age = 15.14 years) investigates changes in adolescents' sleep from low-stress (regular school week) to high-stress times (exam week), and examines the (moderating) role of chronic sleep reduction, baseline stress, and gender. Sleep was monitored over three consecutive weeks using actigraphy. Adolesce...

This volume focuses on the interplay of mind and motion - the bidirectional link between thought and action. In particular, it investigates the implications that this coupling has for decision making. How do we anticipate the consequences of choices and how is the brain able to represent these choice options and their potential consequences? How ar...

In this study the effects of virtual reality exposure therapy (VRET) were investigated in patients with panic disorder and agoraphobia. The level of presence in VRET was compared between using either a head-mounted display (HMD) or a computer automatic virtual environment (CAVE). Results indicate that there was no relationship between the level of...

Insufficient sleep, poor sleep quality and sleepiness are common problems in children and adolescents being related to learning, memory and school performance. The associations between sleep quality (k=16 studies, N=13,631), sleep duration (k=17 studies, N=15,199), sleepiness (k=17, N=19,530) and school performance were examined in three separate m...

Research shows that sleep and the endocrine stress system influence each other. Insufficient and poor sleep are common problems during adolescence. Adolescents are often confronted with high demands concerning cognitive and school performance causing daily life stress especially before and during exam weeks. No study has been conducted investigatin...

End-stage renal disease (ESRD) is an increasing health problem worldwide. Given the increasing prevalence of this disease, the high cost of hemodialysis treatment and the burden of hemodialysis on a patient's life, more research on improving the clinical outcomes and the quality of life of hemodialysis-treated patients is warranted. Sleep disturban...

There were 15 healthy female subjects, differing in their position on the “morningness-eveningness” scale, studied for 7 consecutive days, first while living a sedentary lifestyle and sleeping between midnight and 08:00 and then while undergoing a “constant routine.” Rectal temperature was measured at regular intervals throughout this time, and the...

Little comparative data on sleep-wake rhythms in different dialysis groups exist. The aim of this study was to investigate sleep-wake parameters measured with actigraphy and sleep questionnaires as well as melatonin rhythms in automated peritoneal dialysis, conventional daytime hemodialysis and nocturnal hemodialysis patients. Conventional daytime...

Sleep disturbances have a major influence on quality of life. A commonly used measure of sleep disturbances is sleep efficiency. The purpose of this study was to investigate the prevalence of decreased subjective sleep efficiency in hemodialysis patients. An additional goal was to identify clinical, dialysis or laboratory parameters that are indepe...

The aim of this study was to investigate the effects of exogenous melatonin on sleep-wake rhythm in haemodialysis patients. The study design is a randomized, double-blind, placebo-controlled, cross-over study of 3 x 6 weeks melatonin 3 mg at 22.00 h every night. Haemodialysis patients were asked to fill out a sleep questionnaire and to wear an acto...

End-stage renal disease and its treatment are associated with sleep disturbances such as deterioration of the circadian sleep-wake pattern. Melatonin rhythm, which has an important role in this pattern, is disturbed. The nocturnal melatonin surge is absent in this population. Whether nocturnal in-center hemodialysis changes melatonin and sleep-wake...

Formation of asexual cysts can be induced in Gonyaulax polyedra by melatonin at 15 °C, or by its metabolite, 5‐methoxytryptamine, at 15 or 20 °C. When cells were exposed to a temperature of 10 °C, which holds the circadian oscillator(s), they were almost insensitive to melatonin, and the cyst‐inducing capacity of 5‐methoxy‐tryptamine was reduced to...

Objective: Aims of this study were to investigate the effects of exogenous melatonin on sleep-wake rhythm and on melatonin rhythm in haemodialysis patients. Endogenous melatonin rhythm, which plays an important role in the synchronization of the sleep-wake rhythm, is disturbed in haemodialysis patients. Design: Double-blind placebo-controlled cross...

Objective: To investigate the use of hypnotics and potentially sleep-disturbing medication in the haemodialysis population in comparison to the use in the general Dutch population. The second objective was to investigate the relationship between the use of sleep-disturbing medication and the use of hypnotics. Design and methods: A random sample was...

Slaap is zo gewoon dat we er pas bij stilstaan als we er problemen mee hebben. Hoewel de gemiddelde mens aangeeft tussen de zeven en acht uur slaap per nacht nodig te hebben, komt naar schatting slechts de helft van de westerse bevolking hieraan toe. Zo laat een Nederlandse internetenquête onder ruim 10.000 volwassenen zien dat 53% zeven uur of min...

In this ambulatory study, the relation between daytime functioning and chronic insomnia was investigated. The study sample consisted of 39 chronic insomniacs and 20 healthy control participants. Performance (vigilance, working memory, motor control) and well-being (concentration, fatigue, mood, sleepiness) were assessed by means of a validated test...

"Balancing Interests", the theme of the 17th International Symposium on Shift Work and Working Time held in Hoofddorp, The Netherlands (September 2005), refers to the ambition to reach an optimal balance between the various aspects of shift work. Economic, ergonomic, physical, and psychosocial factors all interact in determining the impact of shift...

This study aimed to examine prospectively whether individual nighttime sleep characteristics at baseline (prior to shift-work exposure) are related to parameters of daytime sleep after commencing shift work. A longitudinal field study was carried out with novice police officers of the Dutch Police Force. A total of 26 subjects were examined at base...

It has been hypothesized that general hyperarousal, present during both sleep and wakefulness, may underlie chronic insomnia. The present study explored, under strictly controlled conditions, whether chronic insomnia is associated with altered physiologic markers of arousal, both in absolute levels and in terms of circadian rhythmicity, relative to...

Insomniacs report daytime functioning problems, but studies of neurobehavioral functioning in insomniacs have shown little objective evidence of impairment. In addition, very little is known about the influence of the circadian clock on performance in chronic insomniacs. In the present study, we investigated whether chronic insomnia is associated w...

Circadian Regulation and Overt Circadian Rhythms in Humans Endogenous and Exogenous Drives for Circadian Rhythms The Circadian and Homeostatic Regulation of Sleep Morningness/Eveningness and Circadian Phenotypes Conclusion Further Reading

Sleep disturbances, in particular restless legs or limb movements, during the night are often reported by uremic patients. However, polysomnography (PSG) studies have never been carried out to confirm the actual occurrence of these disorders and the association with other objective and self-reported sleep-wake data. Forty-eight participants were su...

To investigate the role of the circadian pacemaker in autonomic modulation of base rate cardiac activity, 29 healthy subjects participated in a constant routine protocol. They were randomly divided into two groups in order to manipulate prior wakefulness. Group 1 started at 0900 hours immediately after a monitored sleep period, while group 2 starte...

The role of endogenous circadian rhythmicity in autonomic cardiac reactivity to different stressors was investigated. A constant routine protocol was used with repeated exposure to a dual task and a cold pressor test. The 29 subjects were randomly divided into two groups in order to manipulate prior wakefulness. Group 1 started at 09:00 h immediate...

In dit hoofdstuk wordt eerst besproken wat gerontologie is en welke subdisciplines er zijn. Er zijn verschillende manieren om veroudering bij de mens te bestuderen: via transversaal, longitudinaal en time-lag onderzoek (met verstorende invloeden daarop van leeftijd-, cohort- en periode-effecten) en via onderzoek naar mortaliteit en morbiditeit. Een...

Time course in task performance has been studied extensively. In particular, the investigation of circadian rhythmicity in task performance that varied in complexity. However, these studies disclosed heterogeneous outcomes. This could be the result of confounding exogenous factors, the use of diverse tasks, as well as accumulating sleepiness interf...

In this study characteristics of cardiac functioning were investigated in nine subjects during their nocturnal sleep. The pre-ejection period and the high frequency component of heart rate variability were used as indices of cardiac sympathetic and parasympathetic activity of the autonomic nervous system respectively. Heart rate and the autonomic i...

To investigate the effect of melatonin treatment on health status and sleep in children with idiopathic sleep-onset insomnia. A randomized, double-blind, placebo-controlled trial was conducted in a Dutch sleep center, involving 62 children, 6 to 12 years of age, who suffered more than 1 year from idiopathic chronic sleep-onset insomnia. Patients re...

To investigate the role of the circadian pacemaker in cortisol reactivity to a cold pressor challenge, 26 diurnally subjects participated in a constant-routine protocol and were divided into two groups. Group 1 started immediately after a monitored sleep period at 09:00 h, while group 2 started 12 h later. After 2 h of adaptation, a cold pressor te...

A test battery was constructed on a palmtop computer for ambulatory purposes. This study explored whether the test battery could assess circadian rhythmicity underconstant routine conditions. Performance, body temperature, and subjective sleepiness of 12 healthy subjects were measured. The test battery consisted of a sleepiness questionnaire and th...

The time course of 'sleep inertia' was studied with a semantic priming paradigm. With this automatic spreading activation task it was found that longer reaction times on target words after an awakening from sleep, as compared to those obtained after a period of wakefulness, appeared only during the first 2.5 minutes. Thus, sleep inertia could be ob...

Recently, Stickgold et al. (1999) demonstrated that subjects awakened from REM sleep showed a greater priming effect by weak primes than by strong primes, which is in contrast to the normal pattern of priming. Their interpretation was that REM sleep is involved in enhancing the strength of memory association. To replicate these findings a semantic...

We studied the influence of genetic factors on individual differences in morningness-eveningness in a sample of Dutch twin families. Data were collected from adolescent twins (mean age 17.8 yr) and their parents (mean age of fathers 48.0 yr and of mothers 46.0 yr) and a sample of older twins (mean age 46.5 yr). Scores on morningness-eveningness wer...

To establish the efficacy of melatonin treatment in childhood sleep onset insomnia, 40 elementary school children, 6 to 12 years of age, who suffered more than 1 year from chronic sleep onset insomnia, were studied in a double-blind, placebo-controlled study. The children were randomly assigned to receive either 5-mg melatonin or placebo. The study...

Earlier work has shown that plasma vasopressin levels of depressed patients were higher than those of healthy controls. The aim of the present study was to determine whether plasma vasopressin levels were correlated to parameters of the circadian rhythm. Forty-one patients with major depression and twenty-five controls participated in a case-contro...

The impact of environmental and behavioral factors on the 24-h profile of blood pressure (BP) has been well established. Various attempts have been made to control these exogenous factors, in order to investigate a possible endogenous circadian variation of BP. Recently, we reported the results of the first environmentally and behaviorally controll...

Jet lag is caused by dysregulation of the biological clock and may result in several complaints. First the possibilities to avoid or treat jet lag without the use of drugs are discussed. An alternative method may be the intake of melatonin. This hormone is released by the human pineal gland during the night, but is also available as synthesized age...

The purpose of this study was to compare health-related quality of life of delayed sleep phase syndrome (DSPS) patients with a random Dutch sample and four samples of patients with other chronic conditions. We also investigated the effectiveness of treatment with 5 mg of melatonin on the quality of life of DSPS patients. Forty-three DSPS patients c...

The significance of the phase of circadian rhythmicity for the diagnosis of sleep disturbance was investigated in a group of 80 chronic insomniacs (59 females; mean age 34.8, range 18-59 years). In order to stay close to common clinical practice, data were collected by means of two-week sleep diaries in combination with repeated measurements of sub...

It has been estimated (Bonnet & Arand, 1995) that onethird or more of the normal adult population is suffering from chronic partial sleep loss, at the cost of reduced daytime alertness and productivity on the job and increased risk for human error and sleep-related accidents. The widespread phenomenon of lengthening of sleep at weekends (Valdez et...

Differences in lifestyle may account for a considerable portion of the reported age-related changes in overt circadian rhythmicity. By instructing a group of healthy, noninstitutionalized, elderly subjects and a group of young adults to keep a sleep–wake log for a period of two weeks, and to wear an activity monitor for an overlapping period of 11...

The Sleep Disorders Questionnaire (SDQ) is a 176-item questionnaire designed to diagnose the presence of common sleep disorders. This study set out to assess the validity of a Dutch translation of the SDQ. Scores on 145 questionnaires were analyzed. A cluster analysis of these scores revealed the following clusters: healthy, depression, insomnia, n...

Humans may be subject to seasonal variations, as evidenced by the existence of seasonal affective disorder (SAD) and midwinter insomnia. However, some recent studies have shown that the seasonal variation in the phase of the circadian rhythm is relatively weak in healthy humans. In the present study, evidence is found that there is no seasonal vari...

Using self-report measures, the sleep/wake patterns and several aspects of marital adjustment of 55 couples were established. Preferred sleep/wake pattern and marital adjustment appeared not to be associated; however, couples who were mismatched on actual sleep/wake pattern showed lower marital adjustment than the matched couples.

In a double-blind placebo-controlled cross-over study, 30 patients with Delayed Sleep Phase Syndrome (DSPS) were included, of whom 25 finished the study. Melatonin 5 mg was administered during two weeks in a double-blind setting and two weeks in an open setting successively or interrupted by two week of placebo. The study's impact was assessed by m...

The occurrence of headache and its change after treatment with melatonin 5 mg were studied in 30 patients with delayed sleep phase syndrome. The medication was taken 5 hours before the endogenous nocturnal plasma melatonin concentration had reached 10 pg/mL. Three women (aged 14, 14, and 23 years) suffered from chronic tension-type headache. Their...

Exogenous melatonin, which can be used to treat certain circadian rhythm disorders, maximally advances delayed rhythms when administered 5 hours before the endogenous melatonin starts to increase. The time of the start of the endogenously melatonin is defined as Dim Light Melatonin Onset (DLMO). The DLMO concentration has been defined in serum to b...

Previously, we found that mean plasma concentrations of arginine vasopressin (AVP), but not of oxytocin (OT), were higher in depressed patients than in healthy controls. Plasma AVP concentrations were positively correlated to clinically rated psychomotor retardation. To further explore this previously reported relation we studied psychomotor retard...

Currently available evidence reveals a predominant role of exogenous (so-called “masking”) factors in the 24 h variation of blood pressure in humans. The existence of a (minor) endogenous circadian factor cannot be excluded, however. This possibility was tested by applying the rigorous unmasking conditions of the constant-routine protocol, that is,...

This study investigated a 24-hour variation of subjective mood in 16 healthy Morning-type and 13 Evening-type subjects as defined by the time of day at which their oral temperature curve reached its maximum. The subjects were instructed to use a sleep-wake logbook, in which they kept daily records of the ratings of their mood and alertness for a pe...