International travellers may feel tired and forgetful for up to a month after returning because jet-lag causes long term changes in the brain, according to a US study.
Similar brain disruptions could be experienced by anyone who works alternating night-day shifts or unusual schedules, says the study published in the journal PLOS One, which is the first to look at long-term effects of such lifestyle changes on brain anatomy.
"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 behaviour and function," says Associate Professor Lance Kriegsfeld of the University of California at Berkeley.
The researchers subjected female hamsters to six-hour changes in schedule - similar to a New York to Paris flight - twice a week for four weeks.
As expected, the harried hamsters had trouble learning simple tasks that other, more rested hamsters aced during the four-week period.
But more surprisingly, the learning problems persisted for a month after they settled back into a normal schedule.
Changes to hippocampus
Researchers say they were able to track the changes to a drop in neurons in the hippocampus, which is the part of the brain responsible for memory.
"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," the study's authors say.
Researchers used hamsters because they have such precise circadian rhythms, driven by an internal, 24-hour clock that everyone possesses.
"They will produce eggs, or ovulate, every 96 hours to within a window of a few minutes," says Kriegsfeld.
Graduate student Erin Gibson points out that other studies have shown that people who experience regular jet-lag, display memory loss and learning problems "along with atrophy in the brain's temporal lobe, suggesting a possible hippocampal deficit."
"Our study shows directly that jet lag decreases neurogenesis in the hippocampus," she says.
The finding could have wider implications for shift workers and frequent long-distance travellers, who have already been found to suffer "decreased reaction times, higher incidences of diabetes, heart disease, hypertension and cancer, and reduced fertility," the researchers say.
To ward off the effects, Kriegsfeld advises allowing one day of recovery for every one-hour time zone shift. Night shift workers should sleep in a dark, quiet room to adjust their bodies to their altered schedule.