An objective method of determining the quantity and quality of sleep is to record the electrical activity of the brain (EEG) and motion of the eye (EOG) during the sleep period.
An objective method of determining the quantity and quality of sleep is to record the electrical activity of the brain (EEG) and motion of the eye (EOG) during the sleep period. As an individual goes from an awake to a drowsy state, the EEG dominant frequency decreases in association with a small decrease in amplitude. Similarly, there is a correspondence between the EEG and the various stages of sleep in that there are definite changes in certain wave forms as a person goes from a drowsy to a sleep state. In addition, the periodic appearance of bursts of rapid eye movements (REMs) has been associated with dreaming. Based upon the EEG and EOG characteristics, sleep may be divided by currently accepted criteria into five clinical stages.
There is a definite and well established individual requirement for each sleep stage. A subject's sleep period is characterized by fluctuations in and out of the various stages of sleep. In assessing the quality of a particular sleep period; therefore, the time-duration plot with respect to the sleep stages provide essential information regarding sleep quantity and quality and is referred to as the sleep profile.
In order to accomplish the stated objectives of the experiment it will be necessary to obtain EEG, EOG and head-movement information from the subject continuously during 8-hour sleep periods. The EEG activity will provide the most essential information to the analysis system and will permit detection of the awake state and stages 1 through 4 of sleep. Addition of the EOG data will allow definition of the REM stage of sleep. Detection of head movement will allow the analysis circuitry to ignore sections of data which may be contaminated with artifacts due to head movement in excess of tolerable limits.
The major inflight hardware items required to support M133 are: (a) the cap assembly, which contains the signal sensors; (b) the preamplifier and accelerometer assembly, which fits on top of the cap; (c) the panel assembly, which analyzes, encodes, and records the EEG and EOG data; (d) analog signal tapes, for later more complete analysis and validation of telemetered data; and (e) crew logs, storage and return containers. Power and telemetry are supplied by the spacecraft systems.
Ground-based support facilities include telemetry recorders, analyzers, and displays of sleep-stage information.
Five minutes are needed for preparation (for donning the sleep cap and hardware checkout) and seven minutes after sleep (for doffing, stowage, and hair cleaning). No special crew activities are required to produce these EEG and EOG data, and normal sleep should not be interfered with by the cap and its associated equipment.
The primary EEG and EOG data will be supplemented by crew self-reports on qualitative aspects of the astronaut's sleep status, such as comfort and dreams.
In-flight data analysis of EEG and EOG data will convert the analog signals to 3-bit binary codes for near-real-time telemetry, sampled once every 10 seconds. Seven discrete states will be encoded: awake, 4 stages of sleep depth, rapid eye movements (indicative of dreaming), and head movements. Uncoded continuous analog signals will be type recorded and returned for more detailed post-flight analysis and comparison with in-flight telemetered data.
Near-real-time monitoring and display of sleep data will be available in the mission control center. It will show the astronaut's current sleep-state, cumulative time in each stage, and a graphic continuous sleep-profile display.