Now, a new computer model that simulates these periods of mental wandering may give scientists clues about how our brains work. Specifically, the model shows how our brain cells communicate when our minds are either engaged or idle.

Scientists have known since the late 1990s that our brains still fire off nerve impulses—an indicator of activity—even when they're idle. Since then, scientists have identified several brain networks, called "resting state" networks, inside our gray matter where this phenomenon occurs. (See "Is Your Brain Sleeping While You're Awake?")

Since resting state networks are disrupted in the event of brain injuries and cognitive diseases, modeling them may eventually help people with these conditions, Maurizio Corbetta, of the Washington University School