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
Reaching, grasping, and manipulating: cervical enlargement (spinal
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
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
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
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.