Okay, everyone who thinks they can multi-task, raise your hand (while returning that call from your client). 
There’s a nice summary on NPR about how the brain actually works – which debunks the myth that we can truly multi-task. What the executive function of the brain does (in our frontal lobes) is switch between activities, not to do them simultaneously. We’re actually very good at shifting back and forth between tasks. There are some very practical take-home points here – for example, the fact that you are shutting out one task to do another is an important fact to keep in mind if you’re hurtling along concrete roadways at 65 mpH while answering your phone. It doesn’t take many seconds of inattention to find yourself in another county (and hopefully not spread across it). Another interesting tidbit from this data is the fact that we instinctively avoid “multi-tasking” activities that use the exact same part of the brain (talking on the phone while taking dictation, for example, or what is more popularly known among Doc Gurley circles as the rubbing your tummy while patting the top of your head phenomenon). The reason for this is that it’s too hard for the brain to purge that task and quickly reboot another in the exact same brain-space/activity. The pervasive myth that we all multi-task (and we should multi-task) is hard to resist. Scientifically knowing that constant-shifting-by-shutting-out is the actual process we call multi-tasking might allow some of us to cut back a bit so that we can do a better job at fewer things. Check out the article – not only is the explanation clear, concise and science-based, but it’s also available on audio – so you can listen to it while answering email (ahem).