question: job of a neuron (emergent behavior)
yan king yin (no spam please)
y.k.y at lycos.com
Sat Sep 8 12:22:14 EST 2001
"Matt Jones" <jonesmat at physiology.wisc.edu>:
> In the study of cellular automata (sometimes called artificial life)
> there are a lot of interesting so-called "emergent" behaviors that
> populations exhibit, such as flocking of birds, ants following
> coherent trails, stuff like that.
> Turns out these behaviors, that are only visible at the level of the
> whole population, actually arise from very very simple rules followed
> by each individual. For example, "Head toward the center of mass of
> the flock, but if another bird gets too close then change direction
> randomly." In these systems, the entire population behavior can be
> understood -completely- by knowing what rules the individuals follow.
> What reason do we have to think that brains don't operate in similar
> ways, using very simple rules at the level of each neuron to determine
> the extremely complex behavior at the top?
I have been thinking that the brain has emergent behavior at the level
of neurons. But there is a problem with this idea: The pattern of
innervation inside the brain is specified by genes and is stereotypic,
ie not varying among individuals. For example the corpus collosum
connects the 2 hemispheres, and some genes that code for the
commissure has been identified in the fly. It seems that these patterns
of connection serve specific purposes and they are not random.
If it does not matter how the hemispheres are connected, then we
would expect to find different innervation patterns in different people,
but the fact is they are all anatomically similar.
In other words, if there is emergent behavior, the brain should look
like chaotic, but it is not (when compared among individuals).
It seems that the brain is hard-wired this way in order to maximize
intelligence and adaptive behavior. It could also be for historical
reasons from the phylogeny.
On the other hand some aspects of innervation are activity-dependent
(eg ocular dominance) and therefore emergent.
Is the wiring of the brain also emergent -- determined by a small
number of mechanisms?
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