Saturday, July 21, 2007

* Wider than the sky by Gerald Edelman, Nobel Winner

The genetic code is made of triplets (codons) of nucleotide bases, of which there are 4 kinds: G C A T. Each triplet specifies 1 of 20 different amino acids that make up a protein. Since there are 64 different possible triplet combinations (4x4x4=64), but only 20 amino acids, the codes are degenerate (meaning that multiple codes map to the same amino acid). If it takes a sequence of 300 codons to specify 100 amino acids in a protein, then a large number of the differen base sequences in messages 3^100(3 to the 100th power) can specify the same amino acid sequence. Despite their different structure at the nucleotide level, these degenerate messages yield the same protein. p43

What is the consequence of evolutionary development in which value-category memory was dynamically linked to perceptual categorization? It is the ability to construct a complex scene and to make discriminations between components of that scene. As an animal moves, engaging in many global mappings in response to the world around it, the ongoing parallel signals reentrantly connecting different sensory modalities lead to correlations among complexes of perceptual categories stimulated by objects and events... Signals from the self systems begin even before birth and remain as a central feature of primary consciousness... The ability to construct a conscious state in a fraction of second is the ability to construct a remembered present... For example an animal in the jungle sensing a shift in sounds while the light is diminshed may flee even if there is no casual correlation between these 2 inputs. It is sufficient that the combination of such simultaneous inputs in the past history was previously accompanied by the presence of tiger. Such an animal however may survive without the gift of primary consciousness for some time in a niche. By contrast an animal with the ability to construct a scene can have greater discriminatory capacity and selectivity in choosing its responses. p56-8

No 2 brains are identical, so much so that the same stimulus and reported response triggers different neurons in our brains.

In one set of experiments, no 2 subjects had identical response patterns... Although each subject had a similar response to report (that they saw the same blue or red horizontal or vertical lines), the brain patterns recorded for each subject were individual and unique from those of any other subject... Given the complexity and degeneracy of the environmental and bodily input, there will be no singular mapping for each representation. [You don't have a neuron for President Clinton that lights up everytime you see his picture, nor does another person have a similar neuron.] p110

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