Matt starts to crawl out of bed, having arrived home yesterday after a long flight. He feels dizzy and sees that it is 9 o’clock. This seems like a typical morning, but it isn’t. Actually, it’s not even morning. As Matt notices that the clock actually reads 9:00 P.M., he realizes that he fell asleep sometime in the afternoon and remembers that he was supposed to go on a dinner date. Groggy and now dateless, Matt starts to wonder when he will be able to sleep normally again. Sadly for him, he’s going to be up the entire night due to a sleep disorder all air travelers dread: jet lag.
Millions of travelers annually are affected by jet lag, which causes crippling fatigue during the day and alertness at night. People develop these irregular sleeping schedules when they travel across different time zones (“Jet Lag and Sleep,” 2013). For example, if you travel from Hawaii to New Jersey, you may experience jet lag, since New Jersey’s time zone is six hours ahead of Hawaii’s time zone. So, while your friends are playing a fun Monday afternoon basketball game, you may just be climbing out of bed. This is not because the Aloha State turned you permanently nocturnal – it’s because your body’s sleeping schedule is out of sync with New Jersey’s time.
Jet lag is caused by the body’s inability to adjust its circadian rhythm to a new time zone. The circadian rhythm is basically a biological clock, and it is the 24 hour behavioral and physiological cycle found in numerous organisms (Hall, 1998). The circadian rhythm is the reason why you may get tired every night around 10 P.M., or why you get hungry at lunch time, or why you claim you need to use the bathroom to leave class every day.
The circadian rhythm is controlled by the suprachiasmatic nuclei (SCN), found in the hypothalamus of the brain. The SCN is the body’s central pacemaker. It is a group of about 16,000 neurons that receives information from external stimuli in order to control the cycle of internal processes (Mistlberger, 2005). As a result, the SCN is responsible for making sure our internal clocks are in sync with our external clocks.
Photic stimuli, or light cues, are the main signals that allow the SCN to set the circadian rhythm. When exposed to light, photoreceptors, such as rods and cones, in the eye get excited and send neural signals to the SCN (Refinetti, n.d.).
Non-photic stimuli, such as food availability and temperature, also influence the SCN. However, these stimuli do not have as much impact as the photic cues from the photoreceptors (Refinetti, n.d.).
The SCN uses both the photic and non-photic stimuli to know when to secrete melatonin, the hormone that induces sleep. When we are exposed to light, the SCN tells the pineal gland to decrease melatonin production. On the other hand, when we are not exposed to light, the SCN tells the pineal gland to increase melatonin production to induce sleep (Dubuc, n.d.).
The jet-lagged traveler may see photic cues announcing it is time to sleep or get up, but the SCN is operating in a different time zone. Consequently, it is slow to adjust the rate of melatonin production.
Although it seems like just an inconvenience, jet lag can have much more severe implications than just missed basketball games or dinner dates. In addition to causing exhaustion, people with jet lag have reduced alertness, which can be very dangerous. Numerous fatal motor and plane accidents have been attributed to jet lag. Because of this, the FAA now even requires pilots to rest a minimum of 30 consecutive hours between flights so that they can overcome this sleep saboteur.
Believe it or not, much of our understanding of jet lag has come from research on the degu (Octodon degus), a small rodent that neither flies nor experiences jet lag.
This remarkable rodent can reset its circadian rhythm very easily. In fact, researchers at Stanford University discovered that the degu, which by nature is a diurnal species (meaning it is awake during the day), is able to completely shift its circadian rhythm and become nocturnal. It does this after being exposed to specifically timed light cues that alter its sleep cycle. Since humans are also a diurnal species, researchers hope that a similar treatment can be used for people (Edgar & Kas, 2000).
The same Stanford researchers discovered that the degu is also responsive to non-photic stimuli to adjust its circadian rhythm, which provides more insight into potential treatments. For example, exercise has helped the degu reset its biological clock, allowing the rodent to stay awake longer (Edgar & Kas, 1998). Additionally, orally administered doses of the sleep hormone melatonin have aided the degu in readjusting its sleep schedule, which makes this a possible treatment for humans (Madrid et al., 2007).
Even more impressive, researchers found that the degu has an interesting ability to suppress recovery sleep caused by sleep deprivation. As a result, it can stay active even when sleep-deprived, suggesting that its circadian rhythm can oppose exhaustion to prevent irregular sleeping schedules (Edgar & Kas, 1999).
We have learned much about jet lag from this rodent, and this research is being applied today; one example is specially timed cabin lights on the new Boeing 787 Dreamliner aircraft to ease jet lag.
Maybe one day we’ll have ways to prevent jet lag, too… but until then, I’m going to catch some sleep. I just got back from Korea, and my jet lag is killing me.
Good night (afternoon?)!
- Jet lag affects millions of air travelers annually. It is caused by the body’s inability to adjust its circadian rhythm.
- The degu has remarkable abilities to quickly change its circadian rhythm.
- Research on the degu is providing insight to treatments for jet lag.
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