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January 26, 2011

BehindTheMedspeak: Why are jet-lagged hamsters like flight attendants?


From an item in the November 27, 2010 Wall Street Journal: "Hamsters subjected to simulated jet lag showed diminished neuron production compared with healthy specimens, according to a new study. They also failed a simple learning test. For nearly a month after their schedules stabilized, the hamsters were unable to learn and recall which of two spaces contained a running wheel (a test that healthy animals ace).

"The paper suggests that humans who work rotating shifts or fly frequently may be even more detrimentally affected than previously thought.

"Psychologists moved the hamsters' day-night schedules ahead by six hours, the equivalent of a flight from New York to Paris, eight times in 25 days. Total hours slept didn't change. During the simulated jet lag, neuron production in the hippocampus region of the brain was about half that of healthy hamsters, and remained low for weeks afterward."

Well there it is, then.

The abstract of the paper, published November 24, 2010 in PLoS One, follows.

Note also that you can read and/or download the article in its entirety here.


Experimental 'Jet Lag' Inhibits Adult Neurogenesis and Produces Long-Term Cognitive Deficits in Female Hamsters


Circadian disruptions through frequent transmeridian travel, rotating shift work, and poor sleep hygiene are associated with an array of physical and mental health maladies, including marked deficits in human cognitive function. Despite anecdotal and correlational reports suggesting a negative impact of circadian disruptions on brain function, this possibility has not been experimentally examined.

Methodology/Principal Findings

In the present study, we investigated whether experimental ‘jet lag’ (i.e., phase advances of the light:dark cycle) negatively impacts learning and memory and whether any deficits observed are associated with reductions in hippocampal cell proliferation and neurogenesis. Because insults to circadian timing alter circulating glucocorticoid and sex steroid concentrations, both of which influence neurogenesis and learning/memory, we assessed the contribution of these endocrine factors to any observed alterations. Circadian disruption resulted in pronounced deficits in learning and memory paralleled by marked reductions in hippocampal cell proliferation and neurogenesis. Significantly, deficits in hippocampal-dependent learning and memory were not only seen during the period of the circadian disruption, but also persisted well after the cessation of jet lag, suggesting long-lasting negative consequences on brain function.


Together, these findings support the view that circadian disruptions suppress hippocampal neurogenesis via a glucocorticoid-independent mechanism, imposing pronounced and persistent impairments on learning and memory.


Still with me?

For you, highlights from Robert Sanders' November 24, 2010 UC Berkeley News Center article on the paper follow.


Jet lagged and forgetful? It's no coincidence

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, according to research by University of California, Berkeley, psychologists.

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.”

For air travelers, jet lag is a minor annoyance from which most recover within a few days, perhaps with the help of a melatonin pill. For people who repeatedly cross time zones, such as flight attendants, the effects have been shown to be more serious. Flight attendants and rotating shift workers – people who regularly alternate between day and night shifts – have been found to have learning and memory problems, decreased reaction times, higher incidences of diabetes, heart disease, hypertension and cancer, and reduced fertility. The World Health Organization lists shift work as a carcinogen.

To date, these effects have been documented only in jet-lagged subjects, not after recovery from jet lag, Gibson said. The UC Berkeley study is the first to look at long-term effects as well as changes in brain anatomy.

“The evidence is overwhelming that disruptions in circadian timing have a direct impact on human health and disease,” Kriegsfeld said. “We’ve now shown that the effects are long-lasting, not only to brain function, but likely to brain structure.”

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.

January 26, 2011 at 02:01 PM | Permalink


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I know this comment is not very scientific, but;

I think that is a very neat picture of a hamster, focused just right!

Posted by: Joe Peach | Jan 26, 2011 5:58:59 PM

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