These cells, remarkably, contain the machinery to generate daily, or circadian, rhythms in gene expression and electrical activity.

But the individual cells are sloppy and must communicate with one another to establish a coherent 24-hour rhythm, says Herzog, according to a WUSTL release.

These features make the SCN a flexible clock that can reset to stay in sync in an ever-changing environment. The underlying sloppiness is probably what allows us to adjust to local time when we cross time zones and to vary our sleep cycles with the season, say WUSTL researchers.

The research appeared online in the early edition of the Proceedings of the National Academy of Sciences.