Washington: A new study by researchers at the University of California has indicated that chronic jet lag alters the brain in ways that cause memory and learning problems long after one`s return to a regular 24-hour schedule.
Twice a week for four weeks, the researchers subjected female Syrian hamsters to six-hour time shifts – the equivalent of a New York-to-Paris airplane flight. During the last two weeks of jet lag and a month after recovery from it, the hamsters`` performance on learning and memory tasks was measured.
As expected, during the jet lag period, the hamsters had trouble learning simple tasks that the hamsters in the control group aced. What surprised the researchers was that these deficits persisted for a month after the hamsters returned to a regular day-night schedule.
What`s more, the researchers discovered persistent changes in the brain, specifically within the hippocampus, a part of the brain that plays an intricate role in memory processing. They found that, compared to the hamsters in the control group, the jet-lagged hamsters had only half the number of new neurons in the hippocampus following the month long exposure to jet lag. New neurons are constantly being added to the adult hippocampus and are thought to be important for hippocampal-dependent learning, Kriegsfeld said, while memory problems are associated with a drop in cell maturation in this brain structure.
"This is the first time anyone has done a controlled trial of the effects of jet lag on brain and memory function, and not only do we find that cognitive function is impaired during the jet lag, but we see an impact up to a month afterward," said Lance Kriegsfeld, UC Berkeley associate professor of psychology and a member of the Helen Wills Neuroscience Institute.
"What this says is that, whether you are a flight attendant, medical resident, or rotating shift worker, repeated disruption of circadian rhythms is likely going to have a long-term impact on your cognitive behavior and function."
Kriegsfeld, graduate student Erin M. Gibson and their colleagues reported their findings this week in the online, open-access journal PLoS ONE.
"Other studies have shown that chronic transmeridian flights increase deficits in memory and learning along with atrophy in the brain``s temporal lobe, suggesting a possible hippocampal deficit," said Gibson. "Our study shows directly that jet lag decreases neurogenesis in the hippocampus."
Each of us has an internal, 24-hour clock that drives our so-called circadian rhythm, which is reset every day by small amounts. When a person enters a time zone that is not synched with his or her internal clock, it takes much longer to reset this daily rhythm, causing jet lag until the internal clock gets re-synched.
This acute disruption of circadian rhythms can cause general malaise as well as gastrointestinal problems because the body`s hunger cycle is out of sync with meal times, Kriegsfeld said.
The researchers used hamsters in their study because they are a classic model of circadian rhythms. Their bodily rhythms are so precise, Kriegsfeld said, that they will produce eggs, or ovulate, every 96 hours to within a window of a few minutes.