Why do we spend roughly 10 percent of our waking hours with our eyes closed – blinking far more often than is actually necessary to keep our eyeballs lubricated? Scientists have pried open the answer to this mystery, finding that the human brain uses that tiny moment of shut-eye to power down.

The mental break can last anywhere from a split second to a few seconds before attention is fully restored, researchers from Japan’s Osaka University found. During that time, scans that track the ebb and flow of blood within the brain revealed that regions associated with paying close attention momentarily go offline. And in the brief break in attention, brain regions collectively identified as the ‘Default Mode Network’ power up.

Discovered less than a decade ago, the default mode network is the brain’s ‘idle’ setting. In times when our attention is not required by a cognitive task such as reading or speaking, this far-flung cluster of brain regions comes alive, and our thoughts wander freely. In idle mode, however, our thoughts seldom stray far from home: We contemplate our feelings; we wonder what a friend meant by a recent comment; we consider something we did last week, or imagine […]