I've been doing yoga since 2007, and I've always wondered why on some random days, I can do the Utthita Hasta Padangusthasana pose (at right) with perfect balance, and other days I fall over. I've always wanted to blame it on the teacher or my fellow students, but apparently it has more to do with me and my ability to attune to my own body that day. Huh.
Dan Siegel uses the term "top-down processing" to help us understand neurologically when pre-programmed filters prevent us from being present to our eight senses. In yoga, when we're not attuned to our own bodies, and maybe just copying the form (ie. attuning to) of someone in front of us, it's easier to fall over in this position.
He defines top-down as "how engrained brain states can impinge on emerging neural circuit activations and thus shape our awareness of ongoing experience in the present moment." Basically, how our automatic mental, emotional and instinctual patterns prevent us from experience what's unfolding in our environment.
Our brains are constantly running stimuli through filters that were formed based on our genes, early experiences that shaped our identity, or through some moral code we were taught. The automatic processes of the brain have served us evolutionarily to make quick decisions and be more efficient in our work. As he says, "if every moment of our lives we approached experience as if it were a baby's first step, we would never walk to the market. We must make summations, create generalizations, and initiate behaviors based on a limited sampling of incoming data that have been shunted through the filters of these mental models."
There's a good chance that the part of the brain that deals with the "contextual modulation of neural processing" is in the neocortex, which is the most recently evolved part of the human brain. "The topology of lateral connections within cortical areas is known to embody stored predictions that have been acquired during evolution and through experience-dependent learning."
So when I'm trying to get into the zone in yoga, lifting my leg up to face level and trying to open myself to the bottom-up stimuli of how tippy my standing foot is feeling, how steady that arch is under my foot, and how my leg and glute muscles are jiggling back and forth, I'm also receiving information from the limbic, parietal, and frontal regions of my cortex (again, the top part) about my grocery list, the temperature in the room, and the colorful pigeons that hang out on the window sill outside the studio.
The richness of our lives, says Siegel, depends on our ability to attune to the stimuli that our own bodies are sending us, to free ourselves from the enslavement of our pre-entrained minds.