chaos and neural information processing

[john moody]

It is hard for me to imagine how chaotic behavior could be compu-
tationally  useful.   However,  the fact that our minds wander in
the absence of sensory stimulation or concentration suggests that
the  large  scale  dynamics  of association cortex may in fact be
chaotic at some times. It is not clear however, whether the  mind
is  generally chaotic, sometimes chaotic, marginally unstable, or
(in isolation) simply just ergodic with a very long limit cycle.

However, the brain is not a closed  system,  but  is  subject  to
changing  environmental  inputs and internal chemical and physio-
logical states. This makes dynamical distinctions appropriate for
closed  systems  irrelevant,  except under very controlled condi-
tions. Furthermore, the effects of thermal noise and  the  proba-
bilistic  nature  of  spike  generation and synaptic transmission
make analogies to classical dynamics incomplete at best.

The general question of what regimes of behavior are possible  as
a  function  of  internal  parameters  and  patterns  of  sensory
behavior is none-the-less extremely interesting.

For example, it has already been suggested that certain patholog-
ical  phenomina  such  as epileptic seizures, migraine headaches,
and visual hallucinations are the result of instabilities in oth-
erwise  stable  networks. These instabilities are probably caused
by changes in the balances of neurotransmitters and  neuromodula-
tors.   Jack Cowan (University of Chicago Mathematics Department)
and collaborators have developed some very impressive  mathemati-
cal theories to explain such phenomina.


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