Research

  • Current Research
  • Previous Research

Overview

Quantitative EEG Monitoring of Vigilance: Effects of Sleep Deprivation, Circadian Phase and Sympathetic Activation

Principal Investigator:
Derk-Jan Dijk, Ph.D.

Organization:
Harvard - Brigham and Women's Hospital

NASA Taskbook Entry

Technical Summary

Shuttle astronauts typically sleep only 6 to 6.5 hours per day while in orbit. This sleep loss is related to recurrent sleep cycle shifting - due to mission-dependent orbital mechanics and mission duration requirements - and associated circadian displacement of sleep, the operational demands of space flight, noise and space motion sickness. Such sleep schedules are known to produce poor subjective sleep quality, daytime sleepiness, reduced attention, negative mood, slower reaction times, and impaired daytime alertness. Countermeasures to allow crew members to obtain an adequate amount of sleep and maintain adequate levels of neurobehavioral performance are being developed and investigated. However, it is necessary to develop methods that allow effective and attainable in-flight monitoring of vigilance to evaluate the effectiveness of these countermeasures and to detect and predict online critical decrements in alertness/performance. There is growing evidence to indicate that sleep loss and associated decrements in neurobehavioral function are reflected in the spectral composition of the electroencephalogram (EEG) during wakefulness as well as in the incidence of slow eye movements recorded by the electro-oculogram (EOG). Furthermore, our preliminary data indicated that these changes in the EEG during wakefulness are more pronounced when subjects are in a supine posture, which mimicks some of the physiologic effects of microgravity. Therefore, we evaluated the following hypotheses: (1) that during a 40-hour period of wakefulness (i.e., one night of total sleep deprivation) neurobehavioral function deteriorates, the incidence of slow eye-movements and EEG power density in the theta frequencies increases especially in frontal areas of the brain; (2) that the sleep deprivation induced deterioration of neurobehavioral function and changes in the incidence of slow eye movements and the spectral composition of the EEG are more pronounced when subjects are in a supine position; and (3) that based on assessment of slow-eye movements and quantitative on-line topographical analyses of EEG during wakefulness an EEG and or EOG parameter can be derived/constructed which accurately predicts changes in neurobehavioral function.

In a series of experiments and data analysis projects conducted during the first three years of this project we have established that:

  1. The spectral composition of the EEG during wakefulness exhibits pronounced and predictable changes during a 24-hour period of sustained wakefulness.
  2. The changes associated with sleep loss are most pronounced in EEGs derived from frontal areas of the brain, and in particular so in the delta and theta frequencies, both during wakefulness and during sleep.
  3. Changes in alertness and psychomotor vigilance correlate with changes in EEG power density in the delta and theta frequencies in frontal derivations.
  4. The incidence of slow eye movements during wakefulness increases during sleep loss and correlates with changes in alertness and psychomotor vigilance. This correlation is so tight that inter-individual differences in the time course of the incidence of slow eye movements closely resemble the inter-individual differences in the time course of neurobehavioral performance during a 24-hour episode of sustained wakefulness.
  5. The circadian pacemaker modulates the incidence of slow eye movements as well as the spectral composition of the EEG during wakefulness.
  6. Light-induced changes in the amplitude of the circadian pacemaker and associated changes in the amplitude of the circadian modulation of alertness are associated with changes in the amplitude of the circadian modulation of the incidence of slow eye movements
  7. Light-induced acute changes in alertness are associated with acute changes in the EEG as well as with the incidence of slow eye movements during wakefulness.
  8. Posture modulates the apparent amplitude of the circadian rhythm of body temperature and heart rate such that this amplitude is reduced when subjects are in a supine posture during 40-hour of wakefulness.
  9. Posture modulates the effects of sleep loss and circadian phase on neurobehavioral performance as assessed by the psychomotor vigilance test such that the detrimental effects of sleep loss/circadian phase are more pronounced when subjects are in a supine posture during 40-hour of wakefulness.
  10. The incidence of slow-eye movements during a drowsiness test predicts performance on a psychomotor vigilance task conducted one hour later.

These data, generated by the hypotheses described above as well as by secondary hypotheses, establish that the original hypotheses, specific aims and their modifications as described in the original proposal and subsequent progress reports, were fruitful. These new findings establish a close and robust association of frontal EEG and ocular parameters with changes in neurobehavioral performance in a variety of protocols in which sleep homeostasis and circadian rhythmicity were manipulated. Circadian rhythmicity and sleep homeostasis have been established to be major determinants of performance and our data establish that they are also major determinants of the waking EEG and ocular parameters. This implies that these parameters are likely to be associated with performance in a variety of conditions in which performance is jeopardized by changes in the status of the sleep homeostat or changes in circadian phase.

Furthermore, these data indicate that EEG/EOG based on-line monitoring of alertness/performance can serve as a practical and attainable tool to predict and prevent critical decrements in performance and alertness, without the need to conduct time consuming tests of neurobehavioral performance.

The research conducted in the current grant period aimed at the development of countermeasures for Human performance failure because of sleep and circadian rhythm problems Risk 19, Critical Road Map http://criticalpath.jsc.nasa.gov. In particular, our research relates to the critical questions 6.08 (What are the best methods for monitoring the status of sleep and circadian functioning and for assessing the effects of sleep loss and circadian dysrhythmia that are also portable and non-intrusive in the spaceflight environment?) and 6.21 (What mathematical and experimental models best predict performance problems associated with sleep-wake and work history and circadian rhythm status, and also provide guidelines for successful countermeasure strategies?). In addition, our research is relevant to critical question 6.05 (What are the acute and long-term effects of exposure to the space environment on biological rhythmicity, on sleep architecture, quality, and quantity, and their relationship to performance capability?) and 6.06 (Which countermeasure or combination of behavioral and physiological countermeasures will optimally mitigate specific performance problems associated with sleep loss and circadian disturbances during a Mars mission?).

Further understanding of the relationship between EEG/EOG and neurobehavioral function could thus have a profound effect on the health, productivity and safety of astronauts during space missions.

The research is relevant for the round-the-clock work schedules (day, evening and night work) on the International Space Station, the altered sleep/wake schedule on a Mars surface station, or any other situation where the work-rest schedule is shifted and sleep loss is incurred. It also has relevance for ground personnel monitoring orbiting crew members who must do so working round-the-clock schedules.

This project's funding ended in 2000