resting as scanning

Your mind never rests. (That is essentially why you can experience eureka moments in the unlikeliest places.)  In fact, counter intuitively, the only time your mind (kind of) rests is when you are extremely focused on something. Of course, even in that state, minimality of the level of activity is determined by the nature of what is being focused on. 

For decades, scientists had known that the brain’s “background” activity consumed the lion’s share of its energy. Difficult tasks like pattern recognition or arithmetic, in fact, only increased the brain’s energy consumption by a few percent. This suggested that by ignoring the background activity, neurologists might be overlooking something crucial. “When you do that,” Raichle explains, “most of the brain’s activities end up on the cutting room floor.”

In 2001, Raichle and his colleagues published a seminal paper that defined a “default mode” of brain function—situated in the prefrontal cortex, active in cognitive actions—implying a “resting” brain is perpetually active, gathering and evaluating information. Focused attention, in fact, curtails this scanning activity. The default mode, Raichle and company argued, has “rather obvious evolutionary significance.” Detecting predators, for example, should happen automatically, and not require additional intention and energy.

Daniel A. Gross - This is Your Brain on Silence
 

Evidently, what we perceive as “paying attention” to something originates, at the cellular level, in the synchronized firing of a group of neurons, whose rhythmic electrical activity rises above the background chatter of the vast neuronal crowd. Or, as Desimone once put it, “This synchronized chanting allows the relevant information to be ‘heard’ more efficiently by other brain regions.”

Alan Lightman - Attention