When a person travels over long distances, the place may not be the only change. When his or her body rhythms   get thrown off, he or she suffers from jet lag -- it's hard to sleep and eat at the right times in the new location. Humans and animals have a biological clock in their body that tells them when to sleep, and when to wake. When someone comes to a different place far away, this biological clock takes a while to match the day and night time of the new place. In a new study, reported in November's Science News, researchers at the University of California, Berkeley tested the effects of jet lag on hamsters  . They wanted to know how serious jet lag would affect the brain and thinking habits of the animals. They think what happens to hamsters may happen to humans, too.  In their experiments, the researchers first moved the hamsters' schedules forward by six hours. The animals' eating schedules, for example, were changed. If a hamster was often fed at noon and 4 pm, then it ate at 6 pm and 10 pm on the new schedule. People who travel from China to Europe experience the same shift, since the two regions are about six hours apart, half the shift between China and the USA. After three days, the scientists did it again - they shifted the hamsters' schedules forward by another six hours. Three days after that, they did it again; and then again three days later. For a full month, the scientists changed the hamsters' routines every three days. During the study, the hamsters slept the same amount every day as they did before the study. However, their sleep patterns had a hard time keeping up with the changing schedule. What's more, they seemed to feel low. The researchers also found that the hamsters had trouble with basic learning exercises during the study. The animals' thinking problems didn't go away when the experiment was over. A month after they went back living on a normal schedule, the hamsters still had trouble with basic mental tasks, such as learning and memory. The scientists concluded that serious jet lag has serious side effects, including stupidity  . They are now trying to find out how jet lag is causing these problems, and then it will be possible for them to work out a solution. We can infer from the text that   _  .
The experiments were carried out on a jet plane It is unclear how to avoid jet lag's side effects now Side effects of jet lag will remain in one's whole life Only humans and hamsters have a biological clock