Unraveling the jet-lag asymmetry

Jet lag, the sluggishness we feel after landing in a new time zone, has a directional bias: Studies suggest it takes longer to recover from eastward travel than from westward travel. A new model developed by Michelle Girvan, Edward Ott, Thomas Antonsen, and colleagues at the University of Maryland, College Park, may explain why. The team used tools of nonlinear dynamics to model a region of the brain known as the suprachiasmatic nucleus (SCN), a network of roughly 20 000 time-keeping neurons devoted to maintaining the body’s circadian rhythm. Jet lag happens when those neurons fall out of sync with the local cycle of night and day. Modeling the dynamics of the SCN, however, is a tall order. Although the neurons all take cues from the same source—the retina—they don’t all respond in the same way. Nor do they share the same natural oscillation periods; absent visual cues, the periods of the average person’s SCN neurons would be distributed around an average value slightly longer than a day—about 24.5 hours. In 2008 Ott and Antonsen devised a way to represent such heterogeneous networks of oscillators in terms of just a few key variables. Now they’ve applied that approach to the SCN. Their model predicts that the slight deviation of the neurons’ natural periods from 24 hours can lead to large recovery-time asymmetries. The worst-case scenario turns out to be an eastward trip across nine time zones: An Angeleno arriving in Paris would require six more days to recover than would a Parisian landing in Los Angeles. (Z. Lu et al., Chaos 26, 094811, 2016, doi:10.1063/1.4954275 .)