When you engage in one task at a time, the prefrontal cortex works in harmony with other parts of the brain, but when you toss in another task it forces the left and right sides of the brain to work independently. The process of splitting our attention usually leads to mistakes. In other words, each time our eyes glance away from our computer monitor to sneak a peak at a text message, the brain takes in new information, which reduces our primary focus. We think the mind can juggle two or three activities successfully at once, but Gazzaley says we woefully overestimate our ability to multitask . . .
If you’re working on a project and you stop to answer an email, the research shows, it will take you nearly a half-hour to get back on task.