Chapter 8: Wakefulness and Sleep

• Endogenous rhythms


  Rhythms generated from within the organism, not in response to external stimuli
• Circannual rhythm


  Endogenous rhythm that lasts about a year
• Circadian rhythm


  Endogenous rhythm that lasts about a day
• Animals generate their own rhythms of activity and sleep, even in unchanging environments
• Circadian rhythms affect many physiological processes beyond just sleep and wakefulness
• Humans have a circadian rhythm in body temperature, with a low around 2 hours after sleep onset and a peak around 6 hours before sleep onset
• Humans have a circadian rhythm in mood, with positive mood increasing from waking until late afternoon and then declining until bedtime
• Zeitgeber


  A stimulus that resets the circadian rhythm, such as light, exercise, meals, or temperature
• Light is the dominant zeitgeber for land animals
• People living in the eastern vs western parts of Germany have slightly different sleep midpoints, corresponding to the earlier sunrise in the east
• Blind people can set their circadian rhythms using non-light zeitgebers like noise, temperature, meals, and activity, but some have difficulty maintaining a 24-hour rhythm without light cues
• Clocks in the eastern end of Germany show the time about half an hour earlier than at the western end, even though all people set their clocks to the same time
• Researchers asked adults for their preferred times of awakening and going to sleep and determined for each person the midpoint of those values


  Example: If on weekends and holidays you prefer to go to bed at 12:30 a.m. and awaken at 8:30 a.m., your sleep midpoint is 4:30 a.m.
• People at the eastern edge have a sleep midpoint about 30 minutes earlier than those at the west


  Corresponding to the fact that the sun rises earlier at the eastern edge
• Similar results were found for Turkey and South Africa
• Zeitgebers


  Environmental cues that synchronize circadian rhythms, such as light, temperature, meals, and activity
• Blind people

  • Some set their circadian rhythms by zeitgebers other than light
  • Others who are not sufficiently sensitive to these secondary zeitgebers produce circadian rhythms that are a little longer than 24 hours
  • When their cycles are in phase with the clock, all is well, but when they drift out of phase, they experience insomnia at night and sleepiness during the day
  • More than half of all blind people report frequent sleep problems
• Reported positive mood over time

  • Most pleasant in the late afternoon or early evening, least pleasant around 5 to 7 a.m.
• Astronauts on the International Space Station have 45 minutes of darkness, and when they retreat from the flight deck to elsewhere in the spacecraft, they have constant dim light. As a result, they are not fully alert during their wakeful periods or deeply asleep during rest periods
• On long assignments, many astronauts experience depression and impaired performance
• When we shift to daylight saving time in spring

  Most people remain ill rested for days after the shift
• The adjustment to daylight saving time is especially difficult for people who were already sleep deprived, including most college students
• In fall, when daylight saving time ends, some people have sleep problems then, too
• People who sleep irregularly, such as pilots, medical interns, and shift workers in factories, find that their duration of sleep depends on when they go to sleep
• People who have done shift work for years tend to perform worse than average on cognitive tests
• Night-shift workers

  • Have more accidents than day-shift workers
  • Have great difficulty adjusting their circadian rhythm because most buildings use artificial lighting that is only moderately effective in resetting the rhythm
  • Adjust best to night work if they sleep in a very dark room during the day and work under very bright lights at night, comparable to the noonday sun
  • Short-wavelength (bluish) light helps to reset the circadian rhythm better than long-wavelength light does
• Morning people


  Awaken early, reach their peak of productivity early, and become less alert later in the day
• Evening people


  Warm up more slowly, reaching their peak in the late afternoon or evening
• The tendency for most young people to be evening types causes problems, as high school classes often start at 8:00 a.m. or earlier
• Evening type teenagers tend to get lower than average test scores, especially in their morning classes, even if they have average or above-average intelligence
• Evening type teenagers are more likely than others to use alcohol, overeat, and engage in other risky behaviors
• Morning type people tend to be more moral and honest in the morning, whereas evening type people tend to be more moral and honest in the evening
• Biological clock


  The brain generates its own rhythms, which are insensitive to most forms of interference
• The circadian rhythm remains surprisingly steady despite food or water deprivation, X-rays, tranquilizers, alcohol, anesthesia, lack of oxygen, most kinds of brain damage, or the removal of endocrine organs
• Even an hour or more of induced hibernation often fails to reset the biological clock
• Suprachiasmatic nucleus (SCN)


  The part of the brain that generates the circadian rhythm
• Circadian rhythm


  Internally generated rhythms of activity and sleep lasting about 24 hours, even in an unchanging environment
• It is difficult to adjust to a sleep schedule much different from 24 hours
• Circadian rhythm


  • It continues to operate in constant light or constant darkness
  • The onset of light resets the clock
• When people set their waking and sleeping times by the clock

  The timing of sunrise strongly influences their circadian rhythm