[Neuroscience] Re: motor programs in the brain

r norman via neur-sci%40net.bio.net (by r_s_norman from _comcast.net)
Mon Aug 6 19:48:47 EST 2007


On Mon, 06 Aug 2007 16:52:01 -0700, "rscan from nycap.rr.com"
<rscan from nycap.rr.com> wrote:

>Motor programs in the brain
>
>The first motor program generator (central pattern generator) was
>demonstrated by Wilson in 1961. He showed that an ensemble of neurons
>produced the muscular action required for locust wing action. Since
>then a great deal of work has been done, mostly with invertebrates,
>and with simple circuits. None question that the neural circuits
>involved are constructed by the genome. The molecular activity
>involved in such construction of circuitry by the genome is beyond
>present analysis, but many believe that it will be done.
>
>In vertebrates, the circuitry largely defies analysis, being
>exemplified by populations rather than by individual neurons.
>
>Here is a list of the major motor pattern generators and their
>approximate location within the central nervous system; all cribbed
>from Larry Swanson.
>
>Breathing: ventral medulla/upper cervical cord.
>
>Orofaciopharyngeal movements; facial expression, vocalization,
>licking, chewing, and swallowing: parvicellular reticular nucleus
>(dorsolateral hindbrain).
>
>Reaching, grasping, and manipulating: cervical enlargement (spinal
>cord).
>
>Orienting movements;
>     Eyes (oculomotor): dorsal midbrain reticular core.
>     Head and neck: cervical spinal cord.
>
>Posture: spinal cord.
>
>Locomotion: spinal cord.
>
>Some list! Since none seem to question that invertebrate motor pattern
>generators are constructed by the genome, why should we question
>similar construction by the genome in vertebrates (including man, of
>course). The shift from individual neurons to populations of neurons
>is fundamentally trivial. Also trivial (except to anatomists) is to
>extend the "brain" to include the spinal cord. I so do.
>
>I like to think that a human lifetime can be seen as the genome
>interacting with the environment. Many bridle at such a notion. They
>want to include something from the soul (spirit, essence, psyche,
>mind, consciousness, awareness, intelligence, intellect, mentality,
>self, individuality, persona, personality, conscious mental field,
>self awareness, sentience, executive function), but that is what I
>see.
>
>Motor pattern generators were learned by the genome during four and a
>half billion years of random mutations; nothing is learned after
>conception. Any mutations acquired during meiosis will be passed on to
>the next generation. We are born with a set of motor pattern
>generators. All motor acts follow from these generators. Specifically,
>all phonemes are produced individually from generators. Man can learn
>initiation, variation, control, and expression of a generator, but not
>the generator itself.
>
>Man does not "learn" to walk. The walking circuitry in his brain
>matures, and he walks. The environment alters the expression of the
>locomotion generator so the brain (following the rules of neural
>alteration as set up by the genome, enables the organism to get over
>the ground.
>
>Man's brain matures. In his second year, man starts s to babble (baby
>talk). He does not learn to babble. He just takes pleasure in
>initiating the phoneme generators. Later, then environment will cause
>him to sequence the phoneme generators. He will "learn" a language.
>
>All, not some--but all, motor acts proceed from the initiation of
>motor program generators.
>
>The activity of a motor program generator can be liked to a player
>piano. The holes in the piano roll are the generator. As the roll is
>unrolled, air passes through the holes, passes through tubes, and
>actuates the key mechanisms. Music ensues. The pulses of air, passing
>through the tubes, make up an abstract entity that we may call a
>"program".
>
>Similarly, a motor program generator is activated. Beautifully
>sequenced neural pulses (a motor program) flow through brain circuitry
>until they reach motor neurons. A motor act ensues.
>
>En route, the motor program flows through the ventral anterior-ventral
>lateral complex of the thalamus. Here the motor program is subject to
>the inhibitive influence of the thalamic reticular nucleus. If the
>program is halted (inhibited), the organism pauses. This pause is
>generally called thinking, or hesitating. I intend to speak more of
>thinking in a subsequent post.
>
>Ray Scanlon

Since my own interest is  invertebrate nervous systems, I can't
complain about your insistence on the significance of genetically
determined programs of neural circuits and patterns of activity in all
animals.  However you seem to swing the pendulum far too much in
denying any influence of learning, a process that can easily modify or
modulate genetically determined circuits.  Why not go for the middle
ground and say that genetically programmed patterns, as modified by
conditioning and learning, underlie a lot of vertebrate and mammalian
and primate and hominoid (and human) activity.  Nonetheless, you also
do have to concede that there is also a separate enormous pattern of
behavior especially in the latter group of the above mentioned animals
that is essentially completely learned.  Even something like bird song
varies tremendously in the relative significance of genetic
programming and learning.

And your suggestion that what we call "thinking" is merely a pause in
genetically programmed and controlled motor behaviors strikes me as
rather bizarre, to say the least.

On the more positive side, don't try to extend the notion of "brain"
to the spinal cord.  Just refer instead "central nervous system" and
not to brain.  There is no question that this will include the spinal
cord.  Incidentally, you have to do the same for invertebrates:
Wilson's central pattern generators were located in the thoracic
ganglia, part of the CNS but distinctly not part of the brain.
Invertebrate also have complex pattern generators outside the CNS. The
stomatogastric system of Crustacea is a prime example.  The cardiac
ganglion is perhaps the simplest example of a peripheral pattern
generating neural circuit even though the pattern is by no means
complex.

Also I believe it was Adrian in the early 1930's who showed
spontaneous patterned activity in fish respiratory systems, i.e., a
central pattern generator as opposed to reflex activity or some other
response to stimuli.








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