[Neuroscience] Re: motor programs in the brain

Immortalist via neur-sci%40net.bio.net (by reanimater_2000 from yahoo.com)
Mon Aug 6 21:31:28 EST 2007


On Aug 6, 5:48 pm, r norman <r_s_norman from _comcast.net> wrote:
> On Mon, 06 Aug 2007 16:52:01 -0700, "rs... from nycap.rr.com"
>
>
>
>
>
> <rs... 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.
>

But the genes direct the assembly of the neurons which can be accented
to these various songs. We need a standard that can make it clear
three areas of activity; activities completely determined by the
genes, 2 activities of a mixed nature via nurture and 3 completely
learned and little effect from the genes that direct the assembly of
these capacities. I would wager that most activities in all animals
are the second (2) variety, because I like Ridley's view of nature via
nurture;

Is it nature or nurture that makes us who we are? The question itself
is a false dichotomy;

[someone presents a situation as having only two alternatives, where
in fact other alternatives exist or can exist]

There are copious examples from human and animal behavior, which
present the notion that our environment affects the way our genes
express themselves.

The switches controlling our 30,000 or so genes not only form the
structures of our brains but do so in such a way as to cue off the
outside environment in a tidy feedback loop of body and behavior.

We have genetic "thermostats" that are turned up and down by
environmental factors.

The proof is in the pudding for such touchy subjects as monogamy,
aggression, and parenting, which we now understand have some genetic
controls.

Nevertheless, the more we understand both our genes and our instincts,
the less inevitable they seem.

Not only are nature and nurture not mutually exclusive, but genes are
designed to take their cue from nurture.

Genes are not unchanging little bits of DNA: their expression varies
throughout a person's life, often in response to environmental
stimuli.

Babies are born with genes hard-wired for sight, but if they are also
born with cataracts, the genes turn themselves off and the child will
never acquire the ability to see properly.

On the other hand, stuttering used to be ascribed solely to
environmental factors. Then stuttering was found to be clearly linked
to the Y chromosome, and evidence for genetic miswiring of areas in
the brain that manage language was uncovered. But environment still
plays a role: not everyone with the genetic disposition will grow up
to be a stutterer.

Nature Via Nurture: Genes, Experience,
and What Makes Us Human, by Matt Ridley
http://www.amazon.com/exec/obidos/tg/detail/-/0060006781/

The Agile Gene: How Nature
Turns on Nurture, by Matt Ridley
http://www.amazon.com/exec/obidos/tg/detail/-/006000679X/


> 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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