the liver and the brain

r norman rsn_ at _comcast.net
Wed Sep 1 12:55:57 EST 2004

On 1 Sep 2004 09:30:36 -0700, feedbackdroids at yahoo.com (dan michaels)

>Wolf Kirchmeir <wwolfkir at sympatico.ca> wrote in message news:<d28Zc.16028$CG3.923889 at news20.bellglobal.com>...
>> ray scanlon wrote:
>> > David Longley writes:
>> > 
>> > 
>> >>Don't you think sleight-of-hand and metaphysics deserves derision?
>> > 
>> > 
>> > Well, then let's drop all the sleight-of-hand and metaphysical
>> > prejudices and talk about the brain.
>> > 
>> > Since the neural net (interneurons) appeared in Cnidaria, what has
>> > changed? For one thing, the DNA has evolved to a point where it is
>> > able to construct a whole series of motor program generators, groups
>> > of neurons that when triggered produce a motor act. These generators
>> > can be modified by experience but they are not learned. We are born
>> > with them.
>> > 
>> > The location in the nervous system of some of these motor program
>> > generators can be more or less specified.
>> [...]
>> Are you claiming that we are born able to walk?
>> The development of the motor cortex is actually a good deal more 
>> complicated than you appear to believe. Even in animals that can walk a 
>> few minutes after birth. So I would prefer to say that we are born ready 
>> to learn certain things. If that learning is impeded, we may never learn 
>> to do the things we are "born with."
>This actually brings up something I was thinking about a few days ago
>A lot of ungulates are born able to stand up immediately, and able to
>walk and then run within an hour or so. An evilutionary help in
>improving survival chances, since most ungulates are born into the
>class that might generally be called "prey animal". So good, their
>motor systems are already much more developed at birth than in others
>mammals, such as cats and wolves and humans [the "predator" species].
>The interesting question is whether the perceptual systems of the
>ungulates are already as developed at birth as are their motor
>systems, or whether much of the perceptual development doesn't take
>place after birth, as in cats/humans/etc? It would be advantageous, in
>a survival sense, if a baby zebra could both run away from the lion
>that's chasing it, and also be able to recognize what a lion is,
>shortly after birth. Hmmm ...... ????

The difference you refer to is the distinction between precocial
(capable of function at birth) vs. altricial (helpless at birth).  

See, for example:

  Muir, Brain Res Bull. 2000 Nov 15;53(5):719-26.
  Early ontogeny of locomotor behaviour: a comparison 
     between altricial and precocial animals


  Oppenheim, Anim Behav. 1972 Nov;20(4):644-55. 
  Prehatching and hatching behaviour in birds: a comparative study 
    of altricial and precocial species


For the difference in brain development and function in precocial and
altricial animals, see:
 Sanchez-Villagra and Sultan,  Brain Behav Evol. 2002;59(3):101-13. 
 The cerebellum at birth in therian mammals, with special 
    reference to rodents


  Lossi et al., Ital J Anat Embryol. 2002 Apr-Jun;107(2):117-25. 
  Cell proliferation and apoptosis during histogenesis of the 
     guinea pig and rabbit cerebellar cortex


For the larger discussion of "nature vs. nurture", continuing to
discuss this in the abstract is rather silly.  There is an enormous
literature on the subject.  Here is just a sampling of work:

  Sillar,  Curr Opin Neurobiol. 1994 Feb;4(1):101-7. 
  Synaptic specificity: development of locomotor rhythmicity


  MacKay-Lyons,  Phys Ther. 2002 Jan;82(1):69-83. 
  Central pattern generation of locomotion: a review of the evidence.


  Muir and Chu, J Neurophysiol. 2002 Jul;88(1):117-23. 
  Posthatching locomotor experience alters locomotor development
   in chicks.


This latter one is particular appropriate.  The abstract concludes:
  "Thus locomotor experience is required for normal development of
locomotor behavior, even in very precocial animals. These results are
discussed in terms of the possible neuroanatomical and
neurophysiological mechanisms underlying experience- and
activity-dependent changes during motor development."
  Bussel et al.,  Acta Neurobiol Exp (Wars). 1996;56(1):465-8. 
  Evidence for a spinal stepping generator in man.
    Electrophysiological study.


  Vinay et al.,  Brain Res Brain Res Rev. 2002 Oct;40(1-3):118-29. 
  Development of posture and locomotion: an interplay of endogenously
     generated activities and neurotrophic actions by descending


The evidence is quite clear.  There is good, hard experimental data to
prove that genetically determined motor pattern generating circuits do
exist in mammals in general and humans in particular.  There is also
good, hard experimental data to prove that experience and synaptic
modification is usually necessary to make these circuits function
appropriately to produce useful, responsive, and adaptive behavior in
the functioning organism.

Yes,  Ray, I DO give citations.  We humans are supposed to be able to
learn from the experience of others.  That is a far better method than
just trying to think up things on our own.





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