Counting Sheep: The Science and Pleasures of Sleep and Dreams. Paul Martin

to a minute, often go unnoticed. Suppose a sleepy driver lapses into a microsleep for only ten seconds while driving on a motorway at 70 miles an hour. During that brief, unnoticed lapse in waking consciousness the vehicle will cover about 70 car lengths. It is virtually certain that while you are reading these words someone, somewhere is microsleeping at the wheel of a speeding vehicle.

      One apparent obstacle to prosecuting drivers who fall asleep at the wheel is proving that they were aware of their dangerous state and are therefore legally responsible for their actions. No one could reasonably claim to have been completely unaware that they were dangerously drunk, but a driver might conceivably claim to have been oblivious of being sleepy before crashing. However, the experimental evidence suggests otherwise. Sleep does not occur spontaneously without prior warning in the form of sleepiness.

      Drivers who fall asleep at the wheel may not recall the actual moment of falling asleep, but they will almost certainly remember feeling sleepy beforehand. Scientists established this by monitoring sleep-deprived volunteers while they drove a simulator. The sleepier the drivers felt, the more mistakes they made. Serious errors, of the type that might have caused a crash in real life, were always preceded by prolonged feelings of sleepiness. By the time an ‘accident’ took place the tired driver had invariably been consciously fighting sleepiness for some time. The strong implication is that drivers who fall asleep at the wheel in real life will almost certainly have felt noticeably sleepy beforehand. The problem is that so many sleepy drivers press on regardless, fighting their sleepiness and risking lives. Many drivers harbour the illusion that they will not fall asleep at the wheel provided they fight hard enough. What they fail to appreciate is that if you are sufficiently sleepy you will eventually fall asleep, no matter how hard you resist.

      Not all sleepy drivers are sleepy because of sleep-deprived lifestyles. Some are sleepy because they have a medical sleep disorder, often undiagnosed. The most common of these, called sleep apnoea, involves the repeated interruption of breathing during sleep. We shall be taking a closer look at sleep apnoea in chapter 15. Individuals who suffer from this disorder can become severely sleep-deprived, although they rarely know why. The daytime sleepiness caused by the repeated disruption of their sleep every night can severely impair their driving performance.

      Sleepy drivers not only have more accidents, they also have worse accidents. The hallmark of an accident caused by a driver falling asleep at the wheel is the absence of skidmarks. Of all the crashes that are attributed to drivers falling asleep, more than three quarters involve the car driving off the road and more than half involve high speeds.

      Car and truck manufacturers have done little to tackle the safety hazard created by sleepy drivers. Driver fatigue remains one of the biggest weak spots in vehicle safety, perhaps because it is much easier to modify the design of a vehicle than to modify the behaviour of humans. However, some promising technology is being developed that may show the way. One system uses cameras mounted in the dashboard to track the driver’s eye movements. It exploits the fact that people blink in a characteristic way when they are about to fall asleep. The device warns the driver if the blink frequency indicates a risk of nodding off at the wheel. IBM is developing an even more sophisticated system, known as the Artificial Passenger. An intelligent computer, which knows the driver’s personal profile and interests, holds a conversation with the driver. It asks questions and even tells jokes (though humour is reportedly not yet one of its strengths). If the driver’s responses are slow, flat in intonation and fail to make sense, the Artificial Passenger may judge that the driver is sleepy and urgently needs to be revived. If so, it will automatically open one of the car’s windows, sound an alarm or even activate a device that sprays cold water in the dozing driver’s face.

      Governments are only just beginning to wake up to the carnage caused on our roads by sleepiness, having focused for so long on the dangers of alcohol. And yet sleepiness accounts for far more road deaths than alcohol, let alone drugs.

Sleepy pilots

      My spirits grow dull, and fain I would beguile

      The tedious day with sleep.

      William Shakespeare, Hamlet (1601)

      Fatigue and chronic sleep deprivation are obviously of crucial relevance to aviation safety. Tired pilots are bad pilots, for all the reasons that tired drivers are bad drivers. How big is the problem in practice?

      Historically, severe fatigue among aircrews has sometimes been a major problem during crises where huge demands have been placed on precious personnel. Take, for example, the Berlin airlift of 1948–9. In June 1948 the forces of the former Soviet Union occupying eastern Germany began a blockade of road, rail and other communications between Berlin and the West. An international crisis ensued. The USA and UK mounted a huge airlift operation to supply West Berlin with food and other essential supplies. The airlift continued for 11 months until the Soviets eventually withdrew their blockade. During that time Allied planes delivered more than two million tons of food, fuel and other supplies to the beleaguered residents of West Berlin. To sustain this huge effort, the aircrews worked punishing schedules with grossly inadequate sleep. There were many accidents, some of them the result of fatigue. A special investigation during the crisis led to immediate improvements in the aircrews’ working conditions and sleeping quarters, which probably made a material contribution to the ultimate success of the whole operation.

      Even in peacetime, tiredness is not unknown on the flight deck. Most airline flight crews experience some sleepiness and impairment in their performance, especially during long-haul and overnight flights. In one recent study, scientists from the British Defence Evaluation and Research Agency monitored 12 airline pilots during routine nine-hour flights between London and Miami. Recordings of their EEG brain-wave activity and eye movements revealed that 10 of the 12 pilots either slept or displayed signs of significant sleepiness during the flights. These episodes were often brief, lasting less than 20 seconds. Microsleeps of this brevity generally go unnoticed, and the pilots would probably have been unaware of drifting off.

      Scientists from the NASA Ames Research Center in California also detected fatigue among flight crews on commercial long-haul flights. The crews on these flights, which crossed up to eight time zones, became measurably sleep-deprived. They felt more fatigued than normal, consumed more caffeine, ate more snacks and reported more minor health problems such as headaches, nasal congestion and back pain. Their sleep loss was made worse by the fact that their circadian rhythms did not have time to synchronise with local times. Their natural low points in alertness therefore often occurred while they were on duty, amplifying their sleepiness.

      Jet lag is not just unpleasant and stressful – it also has physical effects on the brain. Researchers compared two groups of female flight attendants who had all been working on long-haul flights for at least five years. Half the women were in jobs that allowed them two weeks to recover between long-distance flights, while the other half usually had only a few days’ rest in between. The women who had little time between flights performed significantly worse on tests of learning and memory; their reactions were slower and they made more mistakes. More significantly, brain scans revealed distinct physical changes in their brains. A region of the brain known as the right temporal lobe had shrunk significantly. The women with the most shrunken right temporal lobes also had the highest levels of cortisol, a stress hormone that is known to affect the structure of the brain and the functioning of the immune system.

      The implication of this research is that people who regularly fly long distances, crossing more than six or seven time zones, should ideally allow at least ten days to recover before doing it again. The research also raises questions about the policies of airlines that require their flight crews to fly long haul without adequate rest periods in between. The thought of sleepy, jet-lagged pilots with wizened right temporal lobes and impaired mental abilities slumped behind the controls of jumbo jets is mildly alarming.

      Flying for a living can be tiring even when it does not involve crossing multiple time zones and becoming jet-lagged. Like workers in many other industries, flight crew are often required to start work early in the morning, and this alone can starve them of sleep. Researchers