Welcome to Your Brain by Sam Wang, Sandra Aamodt Read Free Book Online Page B

study center in Italy. We loved the beautiful setting and the opportunity to get away from our
    day jobs and concentrate on writing, but there was one catch early in the trip: we found ourselves
    writing at three in the morning. At breakfast, we engaged in fascinating conversations with other
    residents, yet sometimes we could barely keep our eyes open.
    Jet lag is a product of modern transportation: horseback, dogsled, and even car travel are slow
    enough that the circadian rhythm can adjust to keep itself in sync with local time. Indeed, the first
    report of jet lag came in 1931, when two pioneering aviators, Wiley Post and Harold Gatty, flew
    around the world in a little less than nine days. They experienced the symptoms we recognize today:
    difficulty getting to sleep, drowsiness, lack of alertness, and digestive problems.
    Jet lag happens when your circadian rhythm has different timing from the external day-night cycle
    in the world. As a result, your brain wants to sleep when it should be awake and vice versa. The
    brain has a master clock, which normally sets the rhythms for body temperature, hunger, and sleep.
    With jet lag, these rhythms can get out of sync with each other, causing symptoms like being hungry in
    the middle of the night.
    How light drives circadian rhythms can be explained by an analogy to a child on a swing. The
    child and swing have a natural period over which one cycle of swinging tends to occur, but if you
    push the swing, it will change speed. Push when the swing is going forward to make it go sooner;
    push when it is coming back, and it goes later. In this way, you can alter the starting time of your daily
    cycle, by exposing yourself to light. To influence your circadian rhythms, though, you must be in the
    light at the right time of day.
    Practical tip: Frequent jet lag and brain damage
    Jet lag is not simply annoying; in repeated doses, it can be dangerous to your brain’s
    health. People who frequently cross many time zones can experience brain damage and
    memory problems. In one study, flight attendants with five years of service who repeatedly
    took less than five days between long trips were compared to flight attendants who had two
    weeks or more between trips. (That’s still a lot of flying!) Both groups flew the same
    number of miles overall. The short-interval group had less volume in the temporal lobe—a
    part of the brain involved in learning and memory. This group also had problems on a
    memory test, suggesting that frequent travel had damaged their brains.
    The brain damage probably resulted from stress hormones, which are released during
    jet lag and are known to damage the temporal lobe and memory. Luckily, unless you work
    for an airline, you probably don’t need to worry about this problem, since very few people
    fly across multiple time zones more often than every two weeks. More likely to be at risk
    are people who do shift work. Like repeated jet travel, frequent drastic changes in working
    hours are likely to cause stress on the body and brain.
    Light acts on circadian rhythms by driving cycles of activity in a tiny region at the bottom of your
    brain called the suprachiasmatic nucleus, which acts as the master clock. The suprachiasmatic
    nucleus receives signals from the eye and also generates its own rhythm. Indeed, cells from the
    suprachiasmatic nucleus grown in a culture dish generate patterns of increasing and decreasing
    activity on an approximately twenty-four-hour cycle. These cells are necessary for normal circadian
    rhythms; animals with damage to the suprachiasmatic nucleus wake and sleep at odd hours.
    Speculation: Morning people and night people
    A tendency to function better at very early or very late hours might result from having a
    natural circadian cycle that is not exactly twenty-four hours long. A twenty-three-hour
    period would encourage early rising in people whose bodies are impatient for the day to

    begin, while the twenty-five-hour person is