A circadian rhythms expert tells NPR why he won’t change the light-dark cycle on rodents in his lab.

TL: What’s the most dramatic effect of a disruption to circadian rhythms that you’ve seen in your own work?

LK: We were quite surprised to see that twice weekly six-hour advances of the light-dark cycle, for four weeks, caused a greater than 50 percent reduction in the birth of new cells in the brains of hamsters. New cells are added every day to the memory center in our brains to help learn and retain new information. This reduction in new cell birth led to dramatic deficits in learning and memory that lasted at least a month after the jet lag ended. We knew jet lag was bad for the brain, but were surprised by how bad!