SEARCH

SEARCH BY CITATION

Keywords:

  • circadian rhythm;
  • handwriting;
  • kinematic analysis;
  • sensorimotor control;
  • sleep deprivation

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The aim of the present study was to determine whether the motor process of handwriting is influenced by a circadian rhythm. Nine healthy young male subjects underwent a 40-h sleep deprivation protocol under constant routine conditions. Starting at 09:00 hours, subjects performed every 3 h two handwriting tasks of different complexity. Handwriting performance was evaluated by writing speed, writing fluency and script size. The frequency of handwriting, as a measure of movement speed, revealed a circadian rhythm, validated by harmonic regression, with a slowing at the time of the onset of melatonin secretion (22:17 hours) and a trough in the very early morning at around 03:30 hours. In the temporal variability of handwriting an effect of task complexity was suggested in the direction of circadian variations in parallel with speed only for the sentence. Despite deficits of speed and temporal variability, writing fluency did not change significantly across sessions indicating that the basic automation of handwriting was preserved at any time. On the second day, daytime levels of the kinematics of handwriting did not reflect impaired performance after sleep deprivation. Our results show for the first time a clear circadian rhythm for the production of handwriting.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

As all living organisms, humans are subject to biological changes in day and night. This chronobiological rhythm is controlled by the circadian clock that times the functions of our body at many levels, from physiologic processes to cognitive performances (Carrier and Monk, 2000). A well-documented circadian rhythm is our body temperature, which shows its maximum in the early evening and its minimum in the early morning hours (Kräuchi and Wirz-Justice, 1994).

Circadian rhythms of gross motor performance were proved for different effectors (e.g. grip strength, maximal torque production of elbow flexors or knee extensors) with a maximum in muscle strength in the early evening and least strength in the early morning (Gauthier et al., 1996; Guette et al., 2005; Stolz et al., 1988). Similar influences of the circadian clock on motor performances are shown for manual dexterity (Peurdue pegboard; Monk et al., 1997), tracking performance (van Eekelen and Kerkhof, 2003) and the spontaneous motor tempo in a finger-tapping task (Moussay et al., 2002). A recent study on time-of-day effects on dexterous object manipulation showed that, when moving a grasped object, grip force decreases in the early evening and increases in the morning (Jasper and Hermsdörfer, 2007).

Handwriting is a highly automated sensorimotor skill frequently performed in everyday life. In skilled handwriting, the basic elements of the handwriting trajectory are up and down strokes, that are characterized by smooth and single peaked (approximately bell-shaped) velocity profiles and therefore provide information about the degree of movement automation (Maarse et al., 1989; Marquardt et al., 1996). Any sophisticated analysis of handwriting movements depends critically on a valid evaluation of movement velocity and acceleration (Marquardt and Mai, 1994). Kinematic analyses of handwriting movements include parameters of writing speed (e.g. writing time and frequency of strokes), fluency (movement automation and temporal variability) and script size (amplitude of strokes) or force parameters such as pen pressure. Handwriting performance can be evaluated very precisely and objectively using such kinematic analyses as demonstrated for example in studies on handwriting impairments in patients with writer’s cramp (Baur et al., 2006; Zeuner et al., 2007), Parkinson’s disease (Tucha et al., 2006a) and depression (Mergl et al., 2004) and in evaluating training procedures (Baur et al., 2009; Mai and Marquardt, 1994; Schenk et al., 2004). Handwriting performance can be examined with a range of tasks, e.g. writing a sentence, producing superimposed circles and writing of repetitive letters. The results of Mergl et al. (1999) suggest that within healthy subjects some handwriting parameters (the temporal variability of handwriting and the degree of movement automation) differentiate between the tasks writing a sentence versus producing circles depending on sex and age.

Only a few studies examined the effect of sleep deprivation on handwriting with inconsistent results. After one night of sleep deprivation Glenville et al. (1978) reported a tendency to write smaller, and a significant time-of-day effect in terms of an increase in writing size in the afternoon compared with the morning. Kim et al. (2001) found no effect on handwriting performance. Tucha et al. examined the quality and the kinematics of handwriting. Sleep deprivation led to significantly faster and more fluent movements but had no influence on the quality of the handwriting specimens, assessed by ratings of legibility and accuracy (Tucha et al., 2006b). Similarly psychoactive substances like caffeine (Tucha et al., 2006c) and nicotine (Tucha and Lange, 2004) seem to influence mainly the kinematics of handwriting performance but not the quality of handwriting specimens.

The circadian rhythm of handwriting has not yet been investigated. Therefore, in the present study, we examined circadian variations in the kinematics of handwriting, as a very precise and objective method. To investigate the circadian rhythm, we used a protocol developed to control for masking effects that modify the endogenous circadian rhythm. Such a constant routine (CR) protocol is characterized by keeping the environmental and behavioral conditions constant while subjects are awake for 40 h (Czeisler et al., 1989; Duffy and Dijk, 2002).

On the basis of the results on handwriting under sleep deprivation or psychoactive drugs, we hypothesized that the kinematics of handwriting might be affected by sleep deprivation. Based on the established circadian rhythms of gross motor performances we expected the kinematics of handwriting to be affected by a circadian rhythm too. Additionally we expected that writing a sentence is more influenced by the circadian rhythmicity than a less complex task of producing superimposed circles.

Materials and methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Participants

The analyzed study sample consisted of nine healthy right-handed male volunteers aged 21–29 years (mean 24.7 ± 3.0 years). Only male participants were included to avoid masking effects due to the female menstrual cycle. Originally the sample included three more participants, however, one participant quit the procedure for acute health reasons and the other participant was excluded from analysis because of instruction problems. Another subject was excluded as he did not comply with the sleep–wake schedule during the week prior to the experiment (mean bedtimes 03:02 hours, mean wake times 11:42 hours). Due to missing saliva samples of one participant, data on melatonin concentration are based on eight participants. All participants were students and non-smokers. All were free from medical, psychiatric and sleep disorders (Pittsburgh Sleep Quality Index score <5, Buysse et al., 1989) and without any diagnosis of task-relevant disorders such as writer’s cramp or dyslexia as assessed by screening questionnaires and a physical examination. Other exclusion criteria were excessive caffeine consumption (more than four cups of coffee or equivalent caffeinated beverages a day), medication or drug consumption, shift work or transmeridian travel within 3 months prior to the study. Participants were asked to keep a regular sleep–wake schedule (bedtimes and wake times within ±30 min of self-selected target time) for 1 week before the experiment began, verified with a wrist actigraph (Actitrac; IM Systems, Baltimore, MD, USA) and sleep diaries. The mean of bedtimes was 00:24 hours (±1:34 h) and the mean of wake times was 08:58 hours (±1:53 h) during the baseline week prior to the beginning of the study. All participants were neither extreme morning nor evening types (midsleep on free days, corrected for sleep deficit, between 04:01 and 05:07 hours (04:32 hours ± 25 min) according to the MCTQ; Roenneberg et al., 2003). All participants gave written informed consent. The protocol, screening questionnaires and consent were approved of the Ethical Committee of the Charité– Universitätsmedizin Berlin.

Protocol

The evening before the CR started participants entered the laboratory and were familiarized with the tasks during a training session. After an 8-h sleep episode, a 40-h sleep deprivation protocol under CR conditions was carried out. During the protocol participants remained in semi-recumbent posture in bed except for needs to go to the toilet. The ambient light levels were maximally 10 lux and room temperature and humidity were held constant. Isocaloric snacks and water were given in hourly intervals. No other meals and drinks were allowed during the CR. Participants performed tasks on a hourly basis out of three test batteries consisting of cognitive, language and motor tasks (results of the other tasks are reported elsewhere) with each test battery recurring every 3 h. One task of the motor test battery was the handwriting task presented here. The first session the handwriting task was performed during the CR was at 09:00 hours. In between the tasks were breaks of 10 min, spent with reading, listening to music or talking to the investigators. Participants were monitored individually by the investigators. The protocol ended with an 8-h recovery sleep in the laboratory.

Assessment of circadian phase and subjective sleepiness

Circadian phase was estimated from salivary melatonin collected at 1 h intervals, starting at 08:00 hours. Saliva samples were assayed for melatonin using a direct double-antibody radio-immunoassay validated by gas chromatography–mass spectroscopy (Bühlmann Laboratories, Allschwil, Switzerland) with an analytical least detectable dose of 0.2 pg mL−1 and a functional least detectable dose of 0.65 pg mL−1 (<20% coefficient of interassay variation; Weber et al., 1997). Subjective sleepiness was assessed with the Karolinska Sleepiness Scale (KSS; Akerstedt and Gillberg, 1990) at the same time as collecting saliva samples for melatonin assay.

Assessment of handwriting performance

Handwriting movements were recorded using a commercially available digitizing tablet (Wacom Intuos3; Wacom Europe GmbH, Krefeld, Germany) with a cable-free, inking writing stylus. The digitizing tablet registered the position of the tip of the writing stylus. The positional data and the force exerted on the tablet by the pen (writing pressure) were transmitted to a personal computer and analyzed with the software CS (CSWin 2007; MedCom, Munich, Germany). The software package CS has been developed for the registration and kinematic analysis of handwriting movements. Sampling frequency was 200 Hz and the accuracy was 0.05 mm in both x and y directions. Velocity and acceleration signals were calculated using a filter method (kernel estimation) optimized for kinematic analysis of handwriting (Marquardt and Mai, 1994).

Participants wrote on a DIN A4 sheet of paper on the digitizing tablet and were encouraged to use their normal style of handwriting before every recording. Zeuner et al. (2007) report that three recordings of the sentence are sufficient to detect abnormalities in writing movements, due to the stability of kinematic parameters. Therefore, we asked our participants to write the German sentence ‘Die Wellen schlagen hoch’ (The waves are surging high) three times and to produce superimposed circles for 3 s in a fluent quick way, without lifting the pen (five times).

Data analysis

For quantitative analysis, the written trace was segmented in subsequent up and down strokes using the software package CS. Kinematic analyses of handwriting were based on the vertical axis of the writing movement, because it is the main direction of position changes during handwriting, while the horizontal component mainly reflects hand transport. We analyzed the following kinematic handwriting parameters:

  • • 
    Duration (in ms) is the time needed to complete the sentence.
  • • 
    The mean frequency (in Hz): the average number of strokes per second as a measure of movement speed.
  • • 
    The mean stroke length in the vertical direction (in mm) as a parameter to estimate script size. The length of the trace written on the paper (in mm) is a further parameter to estimate the script size of writing the sentence.
  • • 
    The mean pen pressure (in N) that was exerted onto the tablet by the tip of the writing stylus.
  • • 
    The mean number of inversions in velocity (NIV) per stroke corresponds to the number of peaks in the velocity profile that is associated with a single up or down stroke. NIV is a variable to measure movement fluency. Perfectly fluent movements are characterized by an NIV = 1.
  • • 
    The mean standard deviation (SD) of stroke duration (in ms) characterizes the temporal variability of handwriting. The larger the SD of stroke duration, the higher is the temporal variability of handwriting.

For all procedures the alpha level was set at 0.05. For each performance variable, only trial data that lay within 2.5 SD of the individual mean were included in statistical analyses. To examine an effect of circadian variation, two-factorial analyses of variance (anovas) for repeated measures with the factors session (sessions 1–13) and task (sentence versus circles) were carried out for each handwriting parameter. All P-values of the analyses were based on the Huynh–Feldt’s corrected degrees of freedom, but the original degrees of freedom are reported. Data are given as mean ± SD. Graphs show the means and error bars (standard error of the mean) after the individual differences were removed by adjusting the individual means inline image to the group means inline image for every participant and any session (inline image; Cousineau, 2007).

An F-tested harmonic regression was used to fit a linear sine function to the data that demonstrated a significant effect of session by anova, allowing for assessment of peak phase and amplitude, and statistical significance of the fit (CircWave V1.4 by Hut, 2007, Groningen, The Netherlands). The harmonic regression analyses were performed with the adjusted variable Y (means after the removing of individual differences).

Subjective sleepiness ratings and salivary melatonin levels were combined into 3-h intervals and analyzed with anovas for repeated measures with the 13-level factor ‘combined session’. Time courses of the handwriting kinematics and circadian phase marker were compared descriptively and according to the fits obtained by harmonic regression.

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Handwriting performance

Fig. 1 shows one participant’s specimens writing the sentence and producing superimposed circles at 18:00 hours of the first day and 03:00 hours. An evaluation of the legibility and uniformity of the handwriting specimens at these two times suggests that the sentence was legible at 03:00 hours just as well as at 18:00 hours (compare Fig. 1a and c). In general it has to be noted that specimens of handwriting of all participants were legible at any session. However, the kinematics of handwriting differed between sessions: the participant needed more time to write the sentence at 03:00 hours and the frequency of strokes was reduced at 03:00 hours (3.92 versus 4.58 Hz at 18:00 hours; Fig. 1a and c). The frequency of strokes when producing superimposed circles was also lower at 03:00 hours (3.68 versus 4.35 Hz at 18:00 hours; Fig. 1b and d). Comparing the pressure writing the sentence at 18:00 and 03:00 hours (Fig. 1a and c), the participant in the example of Fig. 1 exerted increased pressure at 03:00 hours; however, this result does not represent the group data. By contrast, pen pressure producing the superimposed circles was similar at 18:00 (2.86 N) and 03:00 hours (2.83 N) in line with the group data.

image

Figure 1.  Specimens of writing the sentence at 18:00 hours (a) and 03:00 hours (c). Top: the trace of the handwriting (solid line: trace on paper; dotted line: trace in the air); middle: the corresponding vertical velocity (vy) as a function of time; bottom: pen pressure as a function of time. Producing of superimposed circles at 18:00 hours (b) and 03:00 hours (d). Left: the trace of circles; right: the corresponding vertical velocity as a function of time.

Download figure to PowerPoint

Fig. 2 shows the group data. The time course of the experimental data of handwriting performance (dotted lines) and the fitted sine curve (solid lines) are illustrated together with melatonin concentration and sleepiness measures (broken lines) obtained during the 40-h CR protocol.

image

Figure 2.  Kinematics of handwriting and circadian phase markers as a function of time of day. Frequency of up- and down strokes per second writing the sentence (a) and the superimposed circles (b). Temporal regularity (standard deviation (SD) of stoke duration; c) writing the sentence (black square) and superimposed circles (white circles) as deviation from mean. The solid lines show the best fit between the experimental data (dotted lines) and the sine curve obtained from harmonic regression. Subjective sleepiness (d; KSS, 1 = extremely alert, 9 = extremely sleepy) and salivary melatonin concentration (e) combined in 3-h intervals. Error bars represent the standard error of the mean. Asterisks represent the second day of the CR. KSS, Karolinska Sleepiness Scale.

Download figure to PowerPoint

The duration of writing the sentence exhibited a circadian variation (F12,96 = 2.57, < 0.01) with prolonged writing duration between 00:00 and 09:00 hours. The mean time needed to complete the sentence was 9288 ms (±223 ms). A statistically significant (< 0.001) circadian rhythm was documented by harmonic regression with an amplitude of 224 ms (±2.4% of mean level) and the fitted peak phase at 17:37 hours.

The frequency of handwriting also revealed a clear circadian rhythm. The mean writing frequency showed a significant effect of session (F12,96 = 3.22, < 0.01) but no interaction between session and task (< 1). The circadian variation of the frequency in writing a sentence (Fig. 2a) and in producing superimposed circles (Fig. 2b) was simultaneous. At night the frequency of both tasks decreased, but re-increased until noon of the second day reaching approximately the same level as during the first day. The overall level of the frequency was similar for the two tasks [< 1; 4.28 Hz (±0.12 Hz) writing the sentence and 4.32 Hz (±0.11 Hz) producing superimposed circles]. For the frequency of writing a sentence and circles, rhythms were statistically significant fitted by sine functions (< 0.001). The fitted peak phases were noted at 15:35 hours (writing the sentence) and 15:27 hours (writing the circles). The amplitude of the circadian rhythm of writing frequency was 0.14 Hz for the sentence and 0.12 Hz for the superimposed circles (representing ±3.2% of the mean level for the sentence and ±2.7% for the circles).

There was no significant effect of session for stroke length (< 1). While the tasks differed in script size (F1,8 = 12.12, < 0.01) with smaller script size for the sentence (4.44 ± 0.11 mm compared with 7.00 ± 0.21 mm for the circles), there was no significant difference in the time course of the tasks (< 1). The mean length of the trace on paper writing the sentence was 311.7 mm (±7.0 mm) and did not show a significant effect of session (F12,96 = 1.24, = 0.270). Thus, script size did not significantly change during the CR.

The mean pen pressure that was exerted onto the tablet by the tip of the writing stylus did not show an effect of session (F12,96 = 1.11, = 0.368) nor was the interaction between session and task (< 1) significant. However, the effect of task revealed significantly higher pen pressure for the superimposed circles (2.24 ± 0.05 N) compared with the sentence (1.74 ± 0.07 N; F1,8 = 6.26, < 0.05).

Movement fluency did not show an effect of session (F12,96 = 1.45, = 0.171) nor an interaction effect of session and task (< 1). The main effect of task (F1,8 = 26.17, < 0.001) revealed higher movement fluency in the simple writing movements of producing superimposed circles (NIV: 1.04 ± 0.01) compared with the more complex movements of writing a sentence (NIV: 1.18 ± 0.02). The overall (task-specific) low values of NIV showed that the participants wrote and circled in a highly automated control mode.

Fig. 2c depicts the standard deviation of cycle duration for both tasks. The main effect of session of the two-factorial anova for both tasks was not significant (F12,96 = 1.29, = 0.261). The main effect of task was significant (F1,8 = 533.24, < 0.001) with a higher standard deviation of the period time for the sentence (68.5 ± 4.70 ms) than for the circles (13.1 ± 1.24 ms), which is due to the higher variability in writing a sentence. The interaction of session and task of the temporal variability was only a trend (F12,96 = 1.98, = 0.085). However, the harmonic fit for the standard deviation of cycle duration writing the sentence was statistically significant (< 0.01) and localized the fitted peak phase at 15:55 hours with an amplitude of 5.1 ms (representing ±7.4% of the mean level). For writing circles, no statistically significant fit could be found confirming the trend for an effect of task complexity on the circadian time course.

Circadian phase markers

Subjective sleepiness ratings (KSS) showed a circadian rhythm (F12,96 = 13.42, < 0.001; Fig. 2d). The KSS values were quite high right from the start of the CR. The increased level on the second day reflects the effect of sleep deprivation during the CR. Salivary melatonin concentration also revealed a circadian rhythm (F12,84 = 20.37, < 0.001; Fig. 2e), with an onset of averaged melatonin concentration (dim light melatonin onset, DLMO: >3 pg mL−1) in the late evening between 20:35 and 23:43 hours (22:17 hours ± 1:01 h).

Comparisons

The time courses of the duration and the frequency of writing the sentence were very similar. During the first day writing speed increased and sharply decreased after 21:00 hours. Both parameters clearly recovered after 09:00 hours reaching their maximum in the afternoon. The parallel time courses of writing frequency for the two tasks was reflected by the minima obtained by harmonic regression occurring at 03:35 hours (sentence) and 03:27 hours (circles). The time course of the temporal variability showed a maximum in performance in the afternoon and a minimum in the early morning comparable with the frequency. Sleepiness clearly increased after 21:00 hours, which coincided with the DLMO and the sharp decrease in handwriting speed. The minima in the kinematics of handwriting occurred at the same time with the maxima of sleepiness and melatonin concentration at the 03:00 hours session. Subjective sleepiness remained increased the second day, reflecting the sleep deficit, while daytime levels of the handwriting kinematics were almost the same at both days.

Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The present study proved the existence of a circadian rhythm for handwriting movements. At night the duration of writing a sentence was prolonged and the frequency of writing a sentence and superimposed circles was decelerated, i.e. both tasks revealed a circadian rhythm of handwriting speed. In addition, temporal variability was increased at night only in writing a sentence. After the onset of melatonin secretion (22:17 hours) subjects began to rate themselves as ‘sleepy’ (KSS), and simultaneously speed parameters of handwriting sharply decreased. The onset of melatonin secretion in the evening seems to be a hormonal signal for changes in the time course of handwriting kinematics. The relationship between the kinematics of handwriting and subjective sleepiness ratings, however, was less clear, i.e. whether subjects felt more or less sleepy seems to be less important for the time course of handwriting movements. Especially in the early morning of the second day, the level of sleepiness ratings remained on an increased level for several sessions, while the kinematics of handwriting already recovered after the trough between 03:27 and 05:37 hours.

The decrease in writing frequency exhibits some similarities with the early evening decrease in grip force during dexterous object manipulation when moving a grasped object (Jasper and Hermsdörfer, 2007). Similarly, Monk et al. (1997) reported a nocturnal decrease in the performance speed of different tasks (e.g. manual dexterity, serial search and verbal reasoning).

In the present study, the kinematic parameters of handwriting of both tasks showed similar result patterns except for the temporal variability of handwriting. Only in writing the sentence the temporal variability increased during the evening and was the highest shortly before 04:00 hours. By contrast, the variability in producing superimposed circles did not significantly change over the sessions. The effect of task complexity has to be considered with care as the interaction revealed only a trend. However, it was confirmed by a significant fit obtained by harmonic regression for the more complex sentence that was absent for the circles. Mergl et al. (1999) showed in healthy subjects writing a sentence a loss of movement automation with higher age and an effect of gender for the temporal variability of writing the sentence; in producing superimposed circles these parameters were neither affected by age nor by gender. Furthermore, patients with writer’s cramp, who failed writing a sentence, are sometimes still able to produce rapid and automated movements in writing superimposed circles (Mai and Marquardt, 1994). Our finding that the simpler task of circling did not show a circadian rhythm in the temporal variability may thus be due to the fact that it is a very regular movement. By contrast, writing an existing sentence includes a higher diversity of letter forms and, therefore, its temporal variability may be more sensitive to circadian variations. Similarly, Blatter et al. (2005) showed that circadian rhythmicity significantly influenced planning performance only in the more difficult version of a visuo-spatial task. Bratzke et al. (2007) and van Eekelen and Kerkhof (2003), however, showed circadian rhythms independent of task complexity for cognitive tasks.

While the increased level of sleepiness on the second day reflects the effect of sleep deprivation, daytime levels of the kinematics of handwriting did not show impaired performance after a night spent awake. Therefore, sleep deprivation had no effects on the performance of highly automated writing movements. Likewise learning effects due to repetitive execution of the task seemed to be largely absent, although a mutual compensation of learning cannot be completely excluded. In contrast to the findings of Tucha et al. (2006b), in the present study writing fluency did not improve the second day, because participants had already written in a highly automated control mode right from the start. Writing speed did not increase after a night awake either. In skilled writers who write by hand every day, as students normally do, handwriting movements are highly automated and repeatable, reflected by smooth and single-peaked velocity profiles (Marquardt et al., 1996) and therefore no further effect of learning is possible. The fact that fluency did not change significantly across the sessions indicates that despite deficits of speed and temporal variability the automation of handwriting was preserved. The latter might also be the reason, why learning effects due to repetitive execution of the task seemed to be largely absent. In contrast to Glenville et al. (1978), in the present study script size neither changed due to sleep deprivation nor due to a circadian rhythm. Likewise the mean pen pressure that was exerted onto the tablet by the tip of the writing stylus appeared uninfluenced by a circadian rhythm.

In conclusion, the circadian rhythm of the motor process of handwriting is similar to the circadian rhythms of gross motor performances that showed a maximum in muscle strength in the early evening and least strength in the early morning (Gauthier et al., 1996; Guette et al., 2005; Stolz et al., 1988). However, even more than gross motor performances are skilled and dexterous manipulations indispensable for many employees working on shift schedules. Shift-dependent occupational injuries are reported for workers, who rely on their sensorimotor skills, like in an engineering company (Smith et al., 1994) or in textile industry (Nag and Patel, 1998) as well as hospital employees (Horwitz and McCall, 2004). Thus, our finding that a sensorimotor skill like handwriting revealed a circadian rhythmicity is of high ecological relevance.

Acknowledgements

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

We thank the subjects for participation, Prof. Rainer Dietrich, Kathrin Pusch and Jessica Rosenberg for the formidable organization and PD Ingo Fietze, Prof. Thomas Penzel and Martin Glos for enabling the study in their sleep laboratory. Thanks to all investigators for their help in data acquisition and Claudia Renz for analyzing the melatonin data. Thanks to Dr Andreas Zierdt for his support with the plot and Daniel Bratzke and Dr Barbara Baur for helpful comments to the manuscript. This research is part of the Ladenburg Collegium ‘ClockWork’ that is funded by the Gottlieb Daimler- and Karl Benz-Foundation.

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
  • Akerstedt, T. and Gillberg, M. Subjective and objective sleepiness in the active individual. Int. J. Neurosci., 1990, 52: 2937.
  • Baur, B., Schenk, T., Furholzer, W., Scheuerecker, J., Marquardt, C., Kerkhoff, G. and Hermsdörfer, J. Modified pen grip in the treatment of Writer’s Cramp. Hum. Mov. Sci., 2006, 25: 464473.
  • Baur, B., Fürholzer, W., Jasper, I., Marquardt, C. and Hermsdörfer, J. Effects of modified pen grip and handwriting training on writer’s cramp. Arch. Phys. Med. Rehabil., 2009, in press.
  • Blatter, K., Opwis, K., Munch, M., Wirz-Justice, A. and Cajochen, C. Sleep loss-related decrements in planning performance in healthy elderly depend on task difficulty. J. Sleep Res., 2005, 14: 409417.
  • Bratzke, D., Rolke, B., Ulrich, R. and Peters, M. Central slowing during the night. Psychol. Sci., 2007, 18: 456461.
    Direct Link:
  • Buysse, D. J., Reynolds, C. F. III, Monk, T. H., Berman, S. R. and Kupfer, D. J. The Pittsburgh Sleep Quality Index: a new instrument for psychiatric practice and research. Psychiatry Res., 1989, 28: 193213.
  • Carrier, J. and Monk, T. H. Circadian rhythms of performance: new trends. Chronobiol. Int., 2000, 17: 719732.
  • Cousineau, D. Confidence intervals in within-subject designs: a simpler solution to Loftus and Masson’s method. Tutorials Quant. Methods Psychol., 2007, 1: 4245.
  • Czeisler, C. A., Kronauer, R. E., Allan, J. S., Duffy, J. F., Jewett, M. E., Brown, E. N. and Ronda, J. M. Bright light induction of strong (type 0) resetting of the human circadian pacemaker. Science, 1989, 244: 13281333.
  • Duffy, J. F. and Dijk, D. J. Getting through to circadian oscillators: why use constant routines? J. Biol. Rhythms, 2002, 17: 413.
  • Van Eekelen, A. P. and Kerkhof, G. No interference of task complexity with circadian rhythmicity in a constant routine protocol. Ergonomics, 2003, 46: 15781593.
  • Gauthier, A., Davenne, D., Martin, A., Cometti, G. and Van Hoecke, J. Diurnal rhythm of the muscular performance of elbow flexors during isometric contractions. Chronobiol. Int., 1996, 13: 135146.
  • Glenville, M., Broughton, R., Wing, A. M. and Wilkinson, R. T. Effects of sleep deprivation on short duration performance measures compared to the Wilkinson auditory vigilance task. Sleep, 1978, 1: 169176.
  • Guette, M., Gondin, J. and Martin, A. Time-of-day effect on the torque and neuromuscular properties of dominant and non-dominant quadriceps femoris. Chronobiol. Int., 2005, 22: 541558.
  • Horwitz, I. B. and McCall, B. P. The impact of shift work on the risk and severity of injuries for hospital employees: an analysis using Oregon workers’ compensation data. Occup. Med. (Lond.), 2004, 54: 556563.
  • Hut, R. A. CircWave V1.4. 03.2007 Groningen, The Netherlands. Available at: http://www.euclock.org/modules.php?name=Content&pa=showpage&pid=20 (last accessed 03.2008).
  • Jasper, I. and Hermsdörfer, J. Time-of-day effects on force control during object manipulation. Eur. J. Appl. Physiol., 2007, 101: 437444.
  • Kim, D. J., Lee, H. P., Kim, M. S., Park, Y. J., Go, H. J., Kim, K. S., Lee, S. P., Chae, J. H. and Lee, C. T. The effect of total sleep deprivation on cognitive functions in normal adult male subjects. Int. J. Neurosci., 2001, 109: 127137.
  • Kräuchi, K. and Wirz-Justice, A. Circadian rhythm of heat production, heart rate, and skin and core temperature under unmasking conditions in men. Am. J. Physiol., 1994, 267: R819R829.
  • Maarse, F. J., Van Galen, G. P. and Thomassen, A. J. Models for the generation of writing units in handwriting under variation of size, slant, and orientation. Hum. Mov. Sci., 1989, 8: 271288.
  • Mai, N. and Marquardt, C. Treatment of writer’s cramp. In: C.Faure et al. (Eds) Advances in Handwriting and Drawing: A Multidisciplinary Approach. Europia, Paris, 1994: 445461.
  • Marquardt, C. and Mai, N. A computational procedure for movement analysis in handwriting. J. Neurosci. Methods, 1994, 52: 3945.
  • Marquardt, C., Gentz, W. and Mai, N. On the role of vision in skilled handwriting. In: M.Simner, G.Leedham and A.Thomaassen (Eds) Handwriting and Drawing Research. IOS Press, Amsterdam, 1996: 8797.
  • Mergl, R., Tigges, P., Schroter, A., Moller, H. J. and Hegerl, U. Digitized analysis of handwriting and drawing movements in healthy subjects: methods, results and perspectives. J. Neurosci. Methods, 1999, 90: 157169.
  • Mergl, R., Juckel, G., Rihl, J., Henkel, V., Karner, M., Tigges, P., Schröter, A. and Hegerl, U. Kinematical analysis of handwriting movements in depressed patients. Acta Psychiatr. Scand., 2004, 109: 383391.
  • Monk, T. H., Buysse, D. J., Reynolds, C. F. III, Berga, S. L., Jarrett, D. B., Begley, A. E. and Kupfer, D. J. Circadian rhythms in human performance and mood under constant conditions. J. Sleep Res., 1997, 6: 918.
  • Moussay, S., Dosseville, F., Gauthier, A., Larue, J., Sesboue, B. and Davenne, D. Circadian rhythms during cycling exercise and finger-tapping task. Chronobiol. Int., 2002, 19: 11371149.
  • Nag, P. K. and Patel, V. G. Work accidents among shiftworkers in industry. Int. J. Ind. Ergon., 1998, 21: 275281.
  • Roenneberg, T., Wirz-Justice, A. and Merrow, M. Life between clocks: daily temporal patterns of human chronotypes. J. Biol. Rhythms, 2003, 18: 8090.
  • Schenk, T., Bauer, B., Steidle, B. and Marquardt, C. Does training improve writer’s cramp? An evaluation of a behavioral treatment approach using kinematic analysis J. Hand Ther., 2004, 17: 349363.
  • Smith, L., Folkard, S. and Poole, C. J. Increased injuries on night shift. Lancet, 1994, 344: 11371139.
  • Stolz, G., Aschoff, J. C., Born, J. and Aschoff, J. VEP, physiological and psychological circadian variations in humans. J. Neurol., 1988, 235: 308313.
  • Tucha, O. and Lange, K. W. Effects of nicotine chewing gum on a real-life motor task: a kinematic analysis of handwriting movements in smokers and non-smokers. Psychopharmacology, 2004, 173: 4956.
  • Tucha, O., Mecklinger, L., Thome, J., Reiter, A., Alders, G. L., Sartor, H., Naumann, M. and Lange, K. W. Kinematic analysis of dopaminergic effects on skilled handwriting movements in Parkinson’s disease. J. Neural Transm., 2006a, 113: 609623.
  • Tucha, O., Mecklinger, L., Walitza, S. and Lange, K. W. Attention and movement execution during handwriting. Hum. Mov. Sci., 2006b, 25: 536552.
  • Tucha, O., Walitza, S., Mecklinger, L., Stasik, D., Sontag, T. A. and Lange, K. W. The effect of caffeine on handwriting movements in skilled writers. Hum. Mov. Sci., 2006c, 25: 523535.
  • Weber, J. M., Schwander, J. C., Unger, I. and Meier, D. A direct ultrasensitive RIA for the determination of melatonin in human saliva: Comparison with serum levels. J. Sleep Res., 1997, 26: 757.
  • Zeuner, K. E., Peller, M., Knutzen, A., Holler, I., Münchau, A., Hallett, M., Deuschl, G. and Siebner, H. R. How to assess motor impairment in writer’s cramp. Mov. Disord., 2007, 22: 11021109.