First, forget multitasking and try mono-tasking. Focus on just one thing...it may be beneficial.
Next, I have frequently blogged about the default mode or default brain network (Brain Clock posts; IM-HOME post). The default mode (which is estimated to be active approximately 40% of our waking day) has been implicated in how our mind, when idling or resting, is very active--it does not rest while resting. Difficulty quieting the default network has also been implicated in a variety of clinical disorders such as ADHD, Alzheimers, schizophrenia, and autism. This literature is now frequently referred to as mind wandering research (see Brain Clock mind wandering posts). The following is a nice brief overview of the default brain network.
I have also suggested that some brain fitness technologies (Interactive Metronome in particular; conflict of interest disclosure--I serve as a paid external consultant to IM regarding research) are achieving success by either directly or indirectly training controlled, focused attention, which requires shutting down and inhibiting the mind wandering predisposition of the default mode network. I have posted both a set of PPT slides and the video of my recent IM keynote presentation at the Brain Clock blog where I presented the relevant research and hypotheses in detail.
Finally, a more lengthy, thought provoking video is presented last. This video makes it clear that the brain is best conceptualized as an evolving interconnected network.