Life's Potentials 87
Another problem is the fact that, although nerves are essential for
regeneration, the action potentials are silent during the process. No im-
pulses have ever been found to be related to regrowth, and neu-
rotransmitters such as acetylcholine have been ruled out as growth
stimulators.
In addition, impulses always have the same magnitude and speed.
This may not seem like such a big thing either, but think about it. It
means the nerve can carry only one message, like the digital computer's
1 or 0. This is okay for simple things like the knee-jerk reflex. When
the doctor's rubber hammer taps your knee, it's actually striking the
patellar tendon, giving it a quick stretch. This stimulates stretch recep-
tors (nerve cells in the tendon), which fire a signal to the spinal cord
saying, "The patellar tendon has suddenly been stretched." These im-
pulses are received by motor (muscle-activating) neurons in the spinal
cord, which send impulses to the large muscle on the front of the thigh,
telling it to contract and straighten the leg. In everyday life, the reflex
keeps you from falling in a heap if an outside force suddenly bends your
knees.
The digital impulse system accounts for this perfectly well. However,
no one can walk on reflexes alone, as victims of cerebral palsy know all
too well. The motor activities we take for granted—getting out of a
chair and walking across a room, picking up a cup and drinking coffee,
and so on—require integration of all the muscles and sensory organs
working smoothly together to produce coordinated movements that we
don't even have to think about.
No one has ever explained how the
simple code of impulses can do all that. Even more troublesome are the
higher processes, such as sight—in which somehow we interpret a con-
stantly changing scene made of innumerable bits of visual data—or the
speech patterns, symbol recognition, and grammar of our languages.
Heading
the
list
of riddles
is
the
"mind-brain
problem"
of con-
sciousness, with its recognition, "I am real; I think; I am something
special."
Then
there
are
abstract
thought,
memory,
personality,
creativity, and dreams. The story goes that Otto Loewi had wrestled
with the problem of the synapse for a long time without result, when
one night he had a dream in which the entire frog-heart experiment was
reveiled to him. When he awoke, he knew he'd had the dream, but he'd
forgotten the details. The next night he had the same dream. This time
he remembered the
procedure, went to his lab in the morning, did the
experiment, and solved the problem. The inspiration that
seemed to
banish neural electricity forever can't be explained by the theory it sup-
ported! How do you convert simple digital messages into these complex