I was thinking today while walking, that a brain works differently than a computer. A computer, as I envision it, is a single processor, following a bunch of instructions one by one (or a set of processors, nowadays). A processor can switch between threads, but it is still just doing one of them at a time. It's not that simple, but that's how I usually think of it.
But different parts of a brain are working at the same time, parallel, separately. One part is keeping my heart beating - I can't even control that part. One part is keeping me breathing - I have limited control over that part. Other parts are doing things I'm not aware of. When I go for a walk, a part of my brain is controlling the physical aspects of making my body walk, and a part is directing which direction I walk. I have control over these parts, but for the most part I don't have to consciously think about them. Parts of my brain are processing sensory inputs. Some inputs are flagged as unusual, and that may attract the attention of my conscious mind. My conscious mind is sort of like a computer processor - it can really only pay attention to one thing at a time, or it may pay attention to several things by switching between them, one by one.
And yet there are all these other parts of my brain working at the same time... the part right now, which is making my fingers move to type these words in response to my conscious thoughts.
Meditation is not-thinking (as I think of it :).
When I meditate, I try to stop thinking thoughts... I stop thinking words... I may reduce sensory input by closing my eyes and going somewhere relatively quiet. But my brain is still working... still receiving various sensory input. Meditation is not paying attention to those inputs, or not letting those inputs trigger the conscious mind into thinking words. (which goes back to that other question - What are thoughts without words; are they still "thoughts"?) And yet, apparently, meditation still involves paying attention to something... receiving some kind of input... as it is supposed to result in one feeling like something other than a dead rock. Turning off one part of the brain perhaps, but not others. Certainly not all parts, as one still needs to breath, and the heart still needs to beat, and one needs to be open enough to be able to sense the wonder of existence.