Knocking strange doors
FEW areas have received as much attention as the very mundane of human activities - sleep. The annual joint meeting of the American Sleep Disorders Association and Sleep Research Society in Washington Dc recently monitored progress in the field. Participants reviewed two rather interesting studies on sleep: one conducted in space and the other in a submarine. Data on sleep and circadian (occurring once a day) rhythm, obtained from the US space shuttle Columbia and from 20 US submariners is currently being scrutinised. The space and underwater studies could be of particular relevance to others like flight crew, shift-workers and business travellers who flit across time zones. Humans are supposed to be accustomed to a 24-hour cycle, including a sunrise and a sunset. Such experiments shall contribute to our understanding of the effects of removing people from ordinary day/night cues (journal of the American Medical Association, Vol 276, No 8).
Timothy Monk, director of the Human Chronobiology Research Program at the University of Pittsburgh School of Medicine, Pittsburgh, us, led the study of microgravity on humans, involving four of the seven astronauts on board Columbia. Although the Skylab missions of the '70s had done some work in the area, this is t1ge first integrated study of sleep, circadian rhythms and performance in space.
For monitoring their sleep, the astronauts had to wear a hat resembling a swim cap to help position EEG (electroencephalogram) electrodes. Disposable electrodes were used to record eye and chin muscle movements. The measurements were conducted for a 72-hour-period on the third and the 12th day of the mission. These will be compared to the data obtained from the 72-hour-block before the flight and two weeks after their return.
The volunteers were also asked to fill in on details like when they went to sleep, the challenges they had faced during their day-long work, the quality of their sleep and how they felt when they woke up. They also assessed their moods five times a day and took three tests of their mental acuity daily. The astronauts' urine specimens were collected, automatically sampled, labelled and frozen for further analysis for the pattern of secretion of the hormones cortisol and melatonin. While the former provides the start-of-the day signal, the latter appears to set the stage for sleep. In addition, records of temperature and medications, if any, were meticulously jotted down.
Astronauts generally complain of the lack of sleep and other disruptions in the diurnal cycle as they are confined to a narrow and noisy environment. The study may help space scientists tackle the prospect of witnessing a sunrise every 90 minutes better, specially if they are to undertake long-term missions in future.
In the case of the submariners, it was earlier thought that their circadian rhythms got tampered with because they did not see the sun at all for long periods. Tamsin Kelly, who heads the cognitive performance division of the human performance department at the Naval Health Research Centre in San Diego, California, studied the effects of the lack of daylight and sleep deprivation in the submariners. Kelly's group systematically collected samples like saliva for monitoring changes in melatonin levels during different times of the waking period at the start, middle and end of the six-week sea voyage.
Crew members typically lived an 18-hour day: six hours on duty, followed by 12 hours off. The submariners worked for only six hours during their shift studies have shown that as they could not concentrate if they constantly peered into computer screens, listened to sonar or watched dials, if they worked longer. The scientists were surprised to know that the submariners exposed to artificial light developed free-running circadian rhythms if they broke loose from the 24-hour-anchor. The 'men always knew the time of day, ate arid attended roll call at the same time and had normal social contacts with other crew members who remained on a 24-hour-schedule. But these cues, in the absence of exposure to light were not strong enough to maintain their circadian rythms.
Kelly's research has shattered myths on the relationship between human performance, circadian rhythm and sleep cycles. Research hitherto reported from the laboratory of Kelly himself, Monk and others had suggested that the loss of synchrony as it happens in prolonged exposure to 'unnatural surroundings', may undermine performance. Interestingly, no such effects were noticed in the submariners. As Kelly says: "All the data we have collected and analysed so far shows that there is no major compromise in either alertness or sleep and no decrement in performance."