Brain complexity: vision system (Introduction)

by David Turell , Thursday, December 03, 2015, 01:18 (3279 days ago) @ David Turell

The vision we have does not begin at birth. it has to develop as the baby begins to try to see:-http://www.evolutionnews.org/2015/11/brain_neurons_a101211.html-"In the retina, several million nerve cells provide information for more than 100 Million cells in the visual cortex. The visual cortex is one of the first regions of the brain to process visual information. In this brain area, various features as spatial orientation, color and size of visual stimuli are processed and represented.-***-"“Our study shows that self-organization of neuronal circuits in the brain is the most plausible theory for the detailed structure of circuits in the visual system” explains Wolfgang Keil, who graduated from the MPI for Dynamics and Self-Organization and is currently working at Rockefeller University. This result is consistent with the observation that mammals, including us human beings, learn to see after birth. Random networks, which might exist early on, probably do not suffice for full vision.-***-" But through visual experience and dynamic reorganization of connections, the brain rewires itself to such a degree that only little is left from the initial wiring. "Our study shows that self-organization of neuronal circuits in the brain is the most plausible theory for the detailed structure of circuits in the visual system" -***-"The visual cortex does not "see" the outside world. If you were a neuron, operating in the dark inside brain tissue, you would only sense chemical signals coming and going. How would neurons ever "know" how to "self-organize" in such a way that their representations of incoming signals would form a 576-megapixel motion picture that corresponds to the external world? -***-"It's a wonder of nature -- and a darned good thing -- that amid many billions of similar cells in the brain and spinal cord, neurons can extend their tendrillous axons to exactly the right place to form connections, otherwise we wouldn't move, sense, or think properly, if at all.-***-"Interesting as these signals are, they don't explain the larger issue: How do these proteins know when and where to signal? How can a single protein know the "big picture" that the body is aiming for during development? It's analogous to city planners designing a computer center to control the city's traffic signals. Somebody or something with a plan and purpose has to know the overall design goal and how to build it.-***-"Our results also show that Robo3.1 serves as an integrative hub: Its three diverse actions in response to three different cues -- mediating NELL2 repulsion from the motor column, potentiating midline Netrin-1 attraction, and antagonizing midline Slit repulsion -- act simultaneously, are mutually reinforcing, and serve the common purpose of steering commissural axons toward and across the midline. This multiplicity of mechanisms likely helps ensure high-fidelity steering of axons to their targets."-More background:-https://www.mpg.de/9757638/random-wiring-nerves-"The result: random connections do not suffice to explain the observed layout of the brain. The scientists conclude that initially random connections in the visual cortex are reorganized to a precisely determined layout using self-organization. Random wiring, in the end, plays a small role."-Comment: The brain works with us to set up networks that provide excellent vision. This is irreducible complexity, requiring planning and plasticity controls, as the articles indicate. No way Darwin did this.