W H Y T H
E B R A I N
I S N O T
L I K E A
C O M P U T E R
Before going into the design problems created by the physical limitations of genes and neurons a brief description
of three types of injuries to the brain and how they effect vision will drive home the point that there is no ghost in the
machine. If there was a soul watching a video then how does the soul know what
it is watching? Does the soul have a soul watching a video within it, ad infinitum? No, consciousness and vision are entirely a product of brain states.
The association of consciousness with the brain as demonstrated through
brain damage had been noted by the Greeks. Lucretius, setting down the Greek
Atomists philosophy, argued the physical identity of the animus (source of movement and consciousness) with the brain in his
De Rerum Natura (The Nature of Things). They held that both consciousness
and vision involved a different (which they called finer) type of matter. His
example of battle injuries to the brain was used to illustrate the mutability of this finer matter. Cerebral strokes provide a similar illustration of the material nature of consciousness.
I. BRAIN DAMAGE:
Alien Hand Syndrome: It occurs through damage to the anterior cingulate sulcus of either hemisphere at its conjunction with
the corpus callosum (the structure through which occurs nearly all the communication between the two cerebral hemispheres). The right and the left cingulated sulcus make possible the coordinated action of the
left and right hands. Depending on the degree of destruction of this region by
a stroke, behavioral consequences vary. Some patients will deny responsibility
for the action of the effected hand. Some will be unable to detach the effected
hand from an object and must use the other hand to free the object. One patient
found he could bring about the release by saying in a voice Let go! This condition
illustrates how what is normally termed conscious actions can be beyond conscious control.
Achromatopsia: A condition which produces from
partial to complete loss of color vision including sometimes dreams and visual imagination.
It is generally associated with damage to the ventromedial sector of the occipital lobe. The brain damage producing achromatopsia permits the color image producing rods to contribute to the visual
process, but not in color. (Those who are born without rodsa very rare conditionhave
severe visual impairment.) In severe cases of achromatopsia the conscious process
of visualizing is in black and white only.
Prosopagnosia: a condition which results in the inability to recognize faces, and in general between types within a class. Unless the brain damage is extreme, the afflicted person can recognize and describe
the various features of a face. In some cases the patient can discriminate between
faces when asked to match different photographs, estimate age and gender, and recognize various facial expressions such
as surprise, but not identify the faces, even though he previously knew the faces--including his own face. Some patients cannot recognize types within a class, such as makes of cars.
He can tell station wagons & trucks from cars, but not Fords from Lincolns.
This is another illustration of how damage to the brain affects consciousness.
REASONS FOR DESIGN FACETS:
Examples such as the above and many others illustrate how different regions of the brain, some not in the visual cortex,
contribute to the visual process. For a number of reasons the brain has
developed into a organ with dispersed simultaneous processing.
In the early, ancestral lifeforms had different
segments, ganglion for different activities independently. The worm had a segment
of the brain for movement, others for sensing the environment, another for eating.
Each segment operated independently, for the most part. Nature has,
in moving up the rungs of evolutionary complexity, simply increased the cross communication between neural regions and brought
them together. There was no need for a control tower & controller at the
worm level, and such would have been a costly addition. Since no lower-life forms
evolved a control center, the more complex forms simply enlarged upon that design by improving upon communication between
various ganglion centers. For efficiency in communication (shortening of distance
in larger animals), a number of centers were joined together in what evolved into the brain.
Nevertheless, the ganglion still exist in higher animals. The sensory ganglia lie adjacent to either the spinal
cord . . . or the brain stem. The
Nerve cells in sensory ganglia send axons to the periphery that terminate in (or contact) specialized receptors that transduce
information about a wide variety of stimuli (Purves) 6). As the nervous system evolved this facet of specialization and
separate, though interconnected, functions persisted. Latter developments were
based upon the earliest design.
SPEED: Evolution having evolved separate
centers of processing then proceeded to utilize its advantage, speed. It is quicker
to have parallel processing of a sensory signal than linear processing. If this
was done in a linear (assembly line fashion), such an animal would respond much slower than one which utilizes parallel processing. Unlike electronic and fiber-optic signals that proceed at the speed of light, the
neurochemical action inside neurons proceeds at a maximum of 400 feet per second. The
parallel processing of a visual input permits simultaneous determinations as to color, motion, edges, each in its own separate
subsection. From these subsections of the visual cortex run neurons to sections
that sort unto type of object, such as motor vehicle, face, animal, and then to sections which make individual determinations
such as my Honda, my mother, and a squirrel (all this is supported experimentally through the use of implanted microelectrodes). From these sections neurons run to the language and motor centers. Parallel processing produces unique fingerprints with each stimulation of the subsection dealing with motion,
with color, with edges, and so on. There are then connections to other visual
cortical subsections which based on those fingerprints produce a new fingerprint that is then sent to the higher cortical
regions dealing with language. Having the process proceed this way is far more
rapid than in assembly-line fashion.
SIZE: Suppose the visual transmission through the optic nerve and brain were designed to analyze the
visual experience in a linear and television-like fashion. And suppose the homunculus
center was in the language region. This would require a very different brain
design. Suppose there were 100,000 neurons proceeding from each eye to the chism,
and from this point all 100,000 neurons proceeded to the visual cortex. If at
every, let us say one-sixth of a second a bundle of neural stimulation were to proceed in linear fashion, it would have to
go to each of the processing sections one after another. Each sub-processing
center would add to the 200,000 (both eyes) neural signals say 5,000 neural signals containing their determination. It would be like adding to a celluloid film multiple sound tracks, one for each sub-processing center. The film after a couple dozen single sound track additions would be double its original
width. So too would the neural connects gain in width. Then there are other centers that deal with memory and movement in response to the visual image. Such a design would require massive bundles of neurons, comparable to that within the spinal chord. If all this proceed to a center of consciousness, and such was done also for motor
movement, hearing/language, and other functions, there would be a number of large nerve bundles coming to one center.
LIMITATION ON COMPLEXITY OF DESIGN:
What we have is what is possible. Genes simply cannot do the fine
hardwiring required for linear processing. Computer chips have carefully designed,
very complex, etched paths for the linear processing. The brain which weighs
3 pounds and occupies 1,600 cc must rely upon genes to determine the interconnections between its sections and subsections. Given the size and the requirements of the system and the limitations of genes and
the proteins which they express, a duplication like the computer chips etched paths is not possible. Genes can cause bundles of nerves to grow from the spine or in the brain as does the optic nerve and to
follow a specific pathway; however, it cannot cause there to be the precise connection between individual neurons, as we do
when with a telephone switch board or the etched paths on a computer chip. The
gene directed growth process is one of where and what type, not that of which to which.
This is another reason why linear processing is not possible. Genes cannot
control the precise location and connection of each neuron, rather genes control the type of specialize cells, growth
factors effecting the cell (such as the density of dendrites), which neural transmitter the neuron will use, the region where
the neuron will form, the elongation of the neuron to form axons, the connection of axons to other nerve cells, etc. By the very reliance upon chemical growth factors, this places very real limits upon
the design of the brain. Nature cannot produce designs like a computer chip.
One of the fundamental differences between the brain and a computer is
plasticity: usage effects development.
By connecting the striate cortex to the optical out put of the eye through the lateral geniculate, genes determine
the specialization of the striate cortex in conjunction with usage. Those
born congenitally blind (no usage), and who some years later have their vision restored, as with an eye transplant, they never
gain the ability to see with clarity; while those who through trauma loose their vision and then receive an eye transplant,
their vision is restored. In the former the visual cortex has not fully developed. Further evidence of plasticity of development is obtained by the mapping of regions
of the brain in a procedure used prior to operating on some patients with severe epilepsy.
The usage effects development. Computers have the usage determined by
programs and chip design and thus does not have the flexibility to be modified according to usage. The brain is fundamentally different than a computer.