Okay, here's Principle #7, according to Jay Angevine:
"Plasticity
Highly reliable in a healthy person, the human nervous system has inherent modifiability, though in adulthood this attribute cannot approach that in invertebrates (moths and snails) or certain other vertebrates (teleosts and amphibians). In mammalian development, neural plasticity is striking. In continues postnatally. Abnormal visual experience at certain sensitive periods profoundly affects ocular dominance and orientation columns in the visual cortex. If an eye is closed at birth, ocular dominance columns for the other eye enlarge at the expense of adjacent blind eye columns, with thalamic fibers arriving in the cortex expanding terminal fields into them. If, shortly after birth, visual stimuli are restricted for a few weeks or even days to stripes of one orientation, cortical cells develop a response preference to lines of that orientation.
In humans, PET imaging studies of cortical blood flow show that tasks requiring tactile discrimination activate visual cortex in people blind at birth or having lost sight in childhood. This suggests that cortical connections reorganize after blindness: that afferent fibers to nearby cortical areas serving polymodal sensory integration usurp the bereft visual cortex. Such plasticity may explain the well-known tactile acuity of the blind.
In later development, neural plasticity operates on many levels, as in fine-tuning circuits to changing body dimensions. Depth perception is recalibrated as the skull enlarges and interpupillary distance increases. Even in adulthood, plasticity persists. Vilayanur Ramachandran has shown that a stroke with a cottonswab on the cheek of a young man who had accidentally lost his left arm led him to feel touch on his missing left hand. Later, the whole hand could be mapped on his face. The findings suggest that the deprived somatosensory cortical region for the hand becomes innervated by fibers from the adjacent face areas and that secondary input to a cortical neuron's broad receptive field becomes functional when primary input is lost.
After injury to the CNS, intact neurons form new terminals, by axon sprouting, to replace those of other neurons lost to trauma and thus reoccupy vacated synapses. Such reactive synaptogenesis, the clinically proven effectiveness of long-range regrowth of PNS axons, and the evident potential for axon regeneration in the CNS (as in teleosts and amphibia) hold promise for circuit reestablishment. But in mammals, these factors are thwarted by myelin debris, glial scarring, usurpation of sprouts, unresponsive injured neurons, and complex central connections. Developmental neuroscience now focuses on the cerebral cortex. The human nervous system appears to learn very rapidly by using preconstructed circuits and by locking neurons into specific types and functions after cell origin."
So this one is just AWESOME! I was first introduced to this idea of "neuroplasticity" in the book The Brain that changes itself by Dr. Norman Doidge. This book pretty much changed my life and the way I approached therapy and training/conditioning. I COULD go on and on, but I'll keep this one short too. Here goes my observations:
1) The first sentence mentioned in the HEALTHY person that the nervous system is able to be modified but no where close to invertebrates like moths and snails. However, it is still impressive.
2) Dr. Angevine then goes into an example of how loss of sense like vision affects the brain. It seems the neural resources that would have been utilized for vision are re-appropriated and still used. It seems the system has inherent intolerance for low usage of important structures and systems.
3) A special interest to therapists and trainers, the nervous system changes based on dimensions of the body. Well, this is pretty intuitive. Something happens in the body (the skull was used by Angevine) and the nervous system recognizes this and adjusts so as to keep the body trekking on. Amazingly, all of this is under our "conscious" radar.
4) When there is an injury to the body, like a loss of a limb, research has shown that plasticity starts remapping and the sensations of the lost limb can still be "felt." Ramanchandran demonstrated this when by touching the face of a patient who had lost a limb but the tactile sensation was still experienced. Whoa!
5) In the final paragraph, Angevine discusses how the when the CNS is injured it can replace some of the structure in FROGS. Ugh... He explains that the other body processes that accompany the injury can thwart the regeneration; HOWEVER, there was some research done that stated:
"Wernig et al in Proc Natl Acad Sci U S A May (2008) have achieved a real breakthrough. They have been able to convert fibroblasts to neurons. These converted cells form into neurons, glia, and even dopaminergic cells. There has always been concern that converted cells might form tumors, but these scientists painstakingly separated the cells turned into neurons from pluripotential cells with fluorescent stains."
So, there's hope after all. Ordinary cells can be converted into neurons given the proper transcription factors.
This principle is so important to me as a therapist, trainer and coach as we see that changes can occur not only in the body but in the all important nervous system. If our brains couldn't adjust all the REMARKABLE changes that took place in the mesodermal-derived structures like bones, joints, muscles, fascia, etc, we would be always be stuck mentally "small" in a "big" container. I don't think that would be too much fun.
Anyway, this post is running long, so I'll cut it short here.
Questions? Comments? I'd love to see what you're thinking!
In mind, body and spirit,
Will
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