Thursday, May 8, 2008

Nervous System Basics VI: PURPOSEFULNESS

Angevine's fifth basic organizing principle, purposefulness:

"The Purposefulness of Neural Components
Every part of the nervous system has at least one function, often many more. Small parts of the CNS may play crucial roles, as in the extensive distribution and profound influence of axons from inconspicuous brain centers. The locus ceruleus ("blue spot") on each side of the fourth ventricle contains about 12,000 large melanin-pigmented neurons. These synthesize norepinephrine and release it in the cerebral cortex, cerebellum, and almost every other part of the CNS. Electrically, they are almost silent in sleep, hypoactive in wakefulness, and hyperactive in watchful or startling situations. They serve vigilance and attention to novel stimuli. They contribute, indirectly but no less crucially, to perceptual and cognitive functions. By contrast, immense structures make large but expensive contributions, as in the cognitive and motor abilities afforded us by the billions of neurons in our cerebral and cerebellar cortices."

I never have heard such attributes associated with the locus ceruleus before. Fascinating. Another tidbit on locus ceruleus, from Kandel, p. 483:
"...other descending inhibitory systems that suppress the activity of nociceptive neurons in the dorsal horn originate in the noradrenergic locus ceruleus and other nuclei of the medulla and pons. These descending projections block the output of neurons in laminae I and V by direct and indirect inhibitory actions. They also interact with endogenous opioid-containing circuits in the dorsal horn..."
So, locus ceruleus is involved in descending inhibition of pain. Doubly fascinating.

On another topic expanding from this organizing principle, i.e., preconscious genesis/control of conscious thought or action, of ordinary activities we "imagine" to be of our own "free will", much research has demonstrated that, in fact, non-conscious areas of the brain truly run all the decision making activities and simply provide us a grand illusion that we somehow have choice in what we are going to "do" in any given moment.

This can pose a problem if one's concept of the brain is
1. it is monolithic and singular, or
2. if one identifies conscious awareness with the brain itself
3. if one's experience is that when one wants to pick up one's hand, one can, and that's all there is to it.

It may seem odd that nonconscious parts of one's own brain control the behavior and timing of the "I" construct, instead of the other way round. Yet, this is more like how things actually are.

Antonio Damasio's book, The Feeling of What Happens, helps this all fall into place. Reading this book helped my own concept of the brain to change completely from thinking of it as some big homogenous blob up on the top of my body, to an appreciation of the brain as a community of discrete parts that communicate intensely and continuously, a predictor and simulator.

After reading this book, my image of the brain changed to one in which a main, nonconscious "brain", operating autonomously but with my best interests first and foremost, exists in space with two parts attached, a large mobile body attached to the back end, and something called "conscious awareness" affixed (sort of like a miner's head lamp, but easily swiveled) to the front end. The "brain" in the middle can coordinate these two parts easily. (It's a simplistic image but it works for me. In PT, it will take quite awhile before all of us switch from regarding the brain as that blob at the top of the body that is none of our business, to seeing the body as merely the big blob behind the brain, and the brain as the main focus of our interventions.)

There is a trail of research on the timing of conscious awareness as being an after-the-fact phenomenon leading back to Benjamin Libet's Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential): the unconscious initiation of a freely voluntary act. Note the extensive citation list.

Deric Bownds spoke of it recently on MindBlog. Here is a more recent paper he mentioned: Unconscious determinants of free decisions in the human brain.

Additional reading:

1. Books by Benjamin Libet
2. Review of Mind Time, one of the books
3. Publisher comment on another Libet book, The Volitional Brain
4. An analysis of Libet's work by John McCrone

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