motor programs

Rifle River jstream at girch1.med.uth.tmc.edu
Tue May 3 17:14:08 EST 1994


In article <9404302025.AA11938 at bambi.ccs.fau.edu>, tomh at BAMBI.CCS.FAU.EDU
(Tom Holroyd) wrote:

> >Why isn't this a complex program made up of many simpler subprograms?
> 
> Because it's not a "program".  A program is a serially ordered list of
> instructions.

I may misunderstand your point, but your definition seems to indicate that
no animal could ever have a motor program of any sort.  I think you are
trying to conclude that it is wrong to call a behavior a program when it
does not resemble a serial list of instructions.  Did I get this right?

> but the animal has not such set of instructions
> stored anywhere directing the movements.

Without stored instructions (I use this phrase very loosely) how do you get
"instinctive or intrinsic" behaviors?  Isn't the storage of "intrinsic"
behaviors often inherent in the development and the anatomy of the system?
 
> If I put a pan of fluid on the stove and switch on the heat, the fluid
> will organize into convection rolls, and turbulent eddies (if the heat is
> high enough).  There is no stored program telling the fluid how to organize.

But, something forced the fluid to behave in a specific manner.  Wasn't
this due to the physical properties of the heated fluid and the "program"
of thermodynamics?
 
> The action potential in a neuron is a travelling wave in an excitable
> medium; it is not obeying instructions that say "take this information
> from here to there."

But, when the appropriate neurotransmitter binds a nonselective cation
channel, and threshold is exceeded, it is forced to obey the instruction of
take this depolarization from soma to terminal (here to there).  The
instructions are inherent within the properties (voltage dependence) of the
channels.
 
> A complex network of interacting neurons may produce rhythmic temporal
> sequences, but a description like "the large burst of spikes from R30
> is followed by slow spiking from R28 that synchopates with the spikes
> from L28, etc." doesn't tell us anything.

But, say you have a simple animal, like Aplysia, and you fire a neuron and
get a specific behavior.  Then you shock the animal and get the same
behavior.  Next you hyperpolarize the neuron while shocking the animal and
you don't get the behavior etc.  Now you have been told something.  In your
example, just because we don't understand the circuit doesn't mean there
isn't a program (now I really wish I had a better word than program).
 
> And you can't break it down into subsystems, either, because if you take an
> element out of the network the dynamics (and the pattern it produces)
> changes.

First of all, I think it is still useful to study one element at a time. 
Of course, the conclusions drawn would have to be very guarded.  However,
take the example of Aplysia.  What if I can cause a behavior in the intact
animal and then get the exact same behavior when studying only the
subsystem?  Wouldn't this argue against your pattern changes?

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Rifle River                       |   cash value 1/20th of a cent
jstream at girch1.med.uth.tmc.edu    |   void where prohibited
                                  
"We didn't send you to Washington to make intelligent decisions.  We sent
you to represent us."  Kent York, Baptist minister to US Rep. Bill
Sarpalius.



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