Homepage The Computer Inside You Other Writings
essays and commentary
Prev book’s homepage  --|--  table of contents  --|--  entire book in a single web page Next

3 The Bionic Brain

This chapter presents evidence that bions give the brain its intelligence. Also, the basic mechanisms by which learned programs come about are explained. The chapter sections are:

3.1 Neurons

Every mammal, bird, reptile, amphibian, fish, and insect, has a brain. The brain is at the root of a tree of sensory and motor nerves, with branches thruout the body. The building block of any nervous system, including the brain, is the nerve cell. Nerve cells are called neurons. All animal life shows the same basic design for neurons. For example, a neuron from the brain of a man uses the same method for signal transmission as a neuron from a jellyfish.

Neurons come in many shapes and sizes. The typical neuron has a cell body and an axon along which a signal can be transmitted. An axon has a cylindrical shape, and resembles an electrical wire in both shape and purpose. In man, axon length varies from less than a millimeter to more than a meter in length.

A signal is transmitted from one end of the axon to the other end, as a chemical wave involving the movement of sodium ions across the axon membrane. During the wave, the sodium ions move from outside the axon to inside the axon. Within the neuron is a chemical pump that is always working to transport sodium ions to the outside of the cell. A neuron waiting to transmit a signal sits at a threshold state. The sodium-ion imbalance that exists across the axon membrane waits for a trigger to set the wave in motion. Neurons with a clearly defined axon can transmit a signal in only one direction.

The speed of signal transmission thru an axon is very slow compared to electrons moving thru an electrical wire. Depending on the axon, a signal may move at a speed of anywhere from ½ to 120 meters per second. The fastest transmission speeds are obtained by axons that have a myelin sheath: a fatty covering. The long sensory and motor nerves that connect the brain thru the spinal cord to different parts of the body are examples of myelinated neurons. In comparison to the top speed of 120 meters per second, an electrical current in a wire can move more than a million times faster. Besides speed, another consideration is how quickly a neuron can transmit a new signal. At best, a neuron can transmit roughly one thousand signals per second. One may call this the switching speed. In comparison, the fastest electrical circuits can switch more than a million times faster.

One important way that neurons differ from each other is by the neurotransmitters that they make and respond to. In terms of signal transmission, neurotransmitters are the link that connects one neuron to another. The sodium-ion wave is not directly transferred from one neuron to the next. Instead, the sodium-ion wave travels along the axon, and spreads into the terminal branches which end with synapses. There, the synapses release some of the neurotransmitter made by that neuron. The released neurotransmitter quickly reaches those neurons whose dendrites adjoin those synapses, provoking a response to that released neurotransmitter. There are three different responses: a neuron could either be stimulated to start its own sodium-ion wave or inhibited from starting its own sodium-ion wave, or a neuron could have no response.[17]


footnotes

[17] In the human brain there are many different neurotransmitters. Certain functionally different parts of the brain use different neurotransmitters. The subject of neurotransmitters raises the larger question of the affect of various drugs on the mind.

Although it is clear that certain chemicals affect the mind, it does not follow that the mind is a product of chemistry. As an analogy, consider the case of yourself and your physical environment: In your physical environment—including where you live, where you work, where you sleep, and so on—you are surrounded by physical objects, and you interact with many of these physical objects on a regular basis. Now, what happens when your physical environment changes? The change or changes, depending on what they are, may or may not affect you, depending on the specifics of the changes and how you normally interact with the objects in question.

Given this, is an outside observer now entitled to conclude that the part of you that produces your reactions to changes in your physical environment is the same as, or is constructed from, the objects that you are reacting to? Obviously, no. And likewise, it does not follow that just because certain changes in the chemical landscape of the brain can affect the mind, that the mind is a product of chemistry, or is composed of chemicals. Note that the brain is, in effect, the immediate physical environment in which the mind lives.

To generalize the argument: Given that object A is affected by object B, it does not logically follow that object A, or any part of object A, is composed of the same materials as object B.

Regarding psychedelic drugs (Grinspoon, Lester, and James Bakalar. Psychedelic Drugs Reconsidered. The Lindesmith Center, New York, 1997):

The fact that a simple compound like nitrous oxide as well as the complex organic molecule of a drug like LSD can produce a kind of psychedelic mystical experience suggests that the human organism has a rather general capacity to attain the state and can reach it by many different biological pathways. It should be clear that there is no simple correlation between the chemical structure of a substance and its effect on consciousness. The same drug can produce many different reactions, and the same reaction can be produced by many different drugs. [Ibid., p. 36]

Regarding psychiatric drugs (Breggin, Peter, and David Cohen. Your Drug May Be Your Problem. Perseus Books, Reading MA, 1999):

Psychiatric drugs do not work by correcting anything wrong in the brain. We can be sure of this because such drugs affect animals and humans, as well as healthy people and diagnosed patients, in exactly the same way. There are no known biochemical imbalances and no tests for them. That’s why psychiatrists do not draw blood or perform spinal taps to determine the presence of a biochemical imbalance in patients. They merely observe the patients and announce the existence of the imbalances. The purpose is to encourage patients to take drugs.

Psychiatric drugs “work” precisely by causing imbalances in the brain—by producing enough brain malfunction to dull the emotions and judgment or to produce an artificial high. [Ibid., p. 41]

It is perhaps interesting to note that just as one might react to a sudden surplus or deficit in one’s physical environment of some physical object that one uses regularly, by taking actions to return that physical object to its normal quantity and/or affect, so does one react to chemical imbalances in the brain caused by certain drugs. For example:

All four drugs [Prozac, Zoloft, Paxil, and Luvox], known as selective serotonin reuptake inhibitors (SSRIs), block the normal removal of the neurotransmitter serotonin from the synaptic cleft—the space between nerve cells. The resultant overabundance of serotonin then causes the system to become hyperactive. But the brain reacts against this drug-induced overactivity by destroying its capacity to react to stimulation by serotonin. This compensatory process is known as “downregulation.” Some of the receptors for serotonin actually disappear or die off.

To further compensate for the drug effect, the brain tries to reduce its output of serotonin. This mechanism is active for approximately ten days and then begins to fail, whereas downregulation continues indefinitely and may become permanent. Thus, we know in some detail about two of the ways in which the brain tries to counterbalance the effects of psychiatric drugs. There are other compensatory mechanisms about which we know less, including counterbalancing adjustments in other neurotransmitter systems. But, overall, the brain places itself in a state of imbalance in an attempt to prevent or overcome overstimulation by the drugs. [Ibid., p. 46]


Prev Next

http://www.johmann.net/book/ciy3-1.html