Exploring the Human Nervous System (1963)

[Music] I do not know what I may appear to the world, but to myself, I seem to have been only a boy being on the seashore and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before [Music] me. The human nervous system, mysterious and complex, waiting to be explored and understood. We have discovered a few smooth pebbles, but the search has really just begun. Biologists have done detailed studies of the nervous systems of some of the invertebrates, the sea anemone, the hydra. We understand in some detail how this simple animal functions. It receives a stimulus which may mean danger. It reacts by withdrawing. The mechanism that produces this action is relatively uncomplicated. The hydra has a simple food cavity enclosed by a body wall only two cells in thickness. Between the two layers is a network of nerve cells without a spinal cord or brain controlling behavior. Instead, when a sensory cell is stimulated, it triggers impulses which spread in all directions. The whole animal contracts. The simple nerve organization of the hydra with only a few thousand cells would be totally inadequate, however, to control more specialized animals with millions of cells. The earthworm, for instance, has a digestive system, a closed circulatory system with blood vessels, and an elaborate muscular system. Being more complicated, the earthworm needs a more complicated nervous system with a rudimentary brain and a central nerve cord with its chain of ganglia. There is one ganglen to each segment. Each ganglen gives off several nerves. The nerve fibers are differentiated into apherant which carry impulses to the nerve cord and ganglen and epherent which carry the messages to the muscles and organs. But how vastly more complex is this organism? A person can remember what he learned years before about tidepool life. He can watch a crab learn how it protects itself, wonder how its armored shell evolved over how many millions of years. He can also get too curious. A boy's reflex withdrawal is far more complicated than a hydra's, but still an action that we have explored in detail. Pressure stimulates receptors in the skin. These receptors are the end organs of specialized nerve cells or neurons. Actually a great many receptors would be stimulated but for simplicity only one is shown firing here. The nerve impulses travel along the apherant nerve fiber to the spinal cord. We can't even call this pain as yet because pain is an idea that is formulated later in the brain. In the spinal cord, the nerve fiber branches making connection with an intricate complex of other neurons. Contact with the next neuron is made at a syninnapse. The axon of the first neuron makes contact with dendrites or with the body of the second one. The impulse sets up a physicochemical reaction that causes the second neuron to fire. A whole complex of secondary neurons relays the impulses to the motor neurons. The long fibers of these motor neurons finally deliver the impulses to the muscles. To move the 20 or so muscles needed to jerk the finger away from the offending crab, at least four or five spinal nerve trunks are involved. Simple, perhaps? At least it's called a simple reflex arc. Actually, it's not even that simple. Consider for instance the action of a single motor neuron. Aside from the pathway carrying the original impulse, a dozen other pathways may converge on it, each possibly influencing its action. For instance, a fiber from a different part of the chord may slow the firing of the motor neuron. It may stop the firing altogether. Another may speed up the firing. From one part of the brain may come impulses triggered by the organs of vision or hearing or equilibrium. from the higher brain centers may come in order stopping the cowardly retreat, but probably not. No, the simple reflex arc is not terribly simple. But let's get on to a more complicated part of our story. At the time the finger is first nipped, impulses travel up the spinal cord to an inner part of the brain, the phalamus. Here our friend probably experiences his first awareness of pain. In the medela, other circuits are activated. Signals flash to centers in the brain stem and to wide areas of the cerebral cortex. The brain is alerted to the emergency. The pain impulse meanwhile has been relayed to a sensory area of the cortex which localizes the pain in the finger. The eye registers the image of claws and impulses are sent to the visual area of the cortex. Stored someplace in many cells of the brain is the information that claws are threatening. Some mechanism allows our boy to recall this important item which he seems to have forgotten. Impulses travel through association pathways and combined with the sensation of pain arouse fear. Impulses travel back to lower centers where the autonomic nervous system is activated. Autonomic nerve impulses cause the heart to beat faster. blood vessels to constrict, glands to secrete, and other changes. Impulses travel to the frontal area of the cortex where perhaps the judgment is made that this is not a fatal wound. Still other countless pathways are activated. All this in a fraction of a second from one nip of a crab. Of the 10 billion or so neurons in our brains, perhaps three billion fire every second even though there is no crisis. If this incredible complexity seems awesome, remember that knowledge is acquired bit by bit. Of all the elusive mysteries of the brain, memory is perhaps the most fascinating. But what is memory? The crab's pinch causes electrical impulses which somehow leave a lasting imprint. We don't know the exact nature of the imprint yet, but we believe it must involve some change in the chemical compounds of cells of the brain. Probably some rearrangement of atoms. However, the chemical compounds of our bodies are constantly being renewed. A year from now, the compounds that hold the imprint of the crab's pinch will probably be replaced by others. Why isn't the memory lost? There must be some way for the imprint of memory to be transferred to these new substances. Let's see how investigators go about exploring the mystery of memory. Dr. Er, John and his associates at the University of Rochester are among those doing basic research on the problem. Some chemicals seem to serve as blueprints specifying the way in which other substances will be built. Some of these chemicals can even duplicate themselves. One of these substances, ribonucleic acid, RNA for short, seems perhaps to play a role in memory. We have done an experiment to test that possibility. And for that experiment, we chose to use a small flat worm called the plenarian. There were a number of reasons why Dr. John chose this animal. The plenarian has a central nervous system with a rudimentary brain. With this equipment, it is capable of learning. This one is learning a conditioned response. A light is turned on and a second later he's given a slight electric shock. During training, the worm shows little reaction to the light, but the shock causes him to contract. This plenarian has had 500 training trials. Now, if we flash the light alone without the shock, its reaction is very much like the response to shock. It has learned a simple lesson. It has memory. Some change has taken place presumably in the brain. Important to this experiment is the fact that when a plenarian is cut in two, each half will grow to a complete worm. Again, since the head section contains the dominant part of the nervous system, one would expect that a worm which grows from the head section would retain the memory. And so it does. But surprisingly, so does the worm that grows from the tail section. Dr. John's hypothesis was that the RNA in the nerve cells of the tail section is somehow involved in transmitting the memory to the new head. If the RNA in the tail section were destroyed, would that affect the memory? To test this idea, a group of trained pleneria were cut in two. However, this time a chemical that destroys RNA was added to the water. Other trained worms kept in plain pond water were used as controls. After the pleneria had regenerated for about 2 weeks, the head ends that had been in the chemical solution were tested. They continued to respond to the light in the same way that they had before being cut in two. However, the regenerated tail ends that had been in the chemical solution reacted as if they had not been trained at all. Evidently, the tail section was unable to transmit the learning to its new head. It is reasonable to think that this was because the RNA was destroyed at the cut surface. Like most experimental results, other explanations also seem reasonable and so further work must be done to narrow down the possibilities. Science is a business of converging to the truth. We and many others are working on other studies in this field. Each study provides one small bit of information. Enough such bits and someday we will understand memory. Another major area of research covers the electrical activity of the nervous system. A principal research tool is the electronphilograph or EEG. The EEG records the spontaneous electrical activity of the brain. To the untrained person, normal tracings look like random squiggles at first, but even a quick look reveals two very different kinds of wave patterns. Small rapid movements called beta waves are usually most prominent toward the front of the head. Larger, slower alpha waves are most prominent at the back of the head. One significant fact is that alpha waves change abruptly when a person is alerted. For instance, if the person just opens his eyes, the alpha waves disappear. Close and they reappear. Watch again. There has been an upsurge of research into the electrical activity of the nervous system since investigators have learned to implant electrodes deep in the brain. Electrodes can stay in the brain without pain or injury. Among those investigating electrical activity is Dr. Ross Ady of UCLA. We are interested in the way the brain stores information as a memory trace. To study this phenomenon, we have developed an electrical technique which allows us to measure the resistance of brain tissue. We implant a special double electrode into the brain and with it measure the resistance of small amounts of brain tissue. The monkey that you see here has special miniature plastic sockets on its head which permit the connection of these deep brain probes with external measuring devices. The double electrode has been implanted in a deep region of the brain which is known to be important in the process of storing information. The tips of the electrode rest in the brain tissue. An electrical current going from one pole to another must pass through the brain tissue which sets up a certain amount of resistance to the current. Dr.'s idea was to find out if any differences in resistance occur in the brain tissue after new information has been stored in it. To conduct this experiment, the monkey had to be given something new to learn. Equipment was constructed on which three lighted symbols appear in different combinations. Pressing one of the two similar ones makes the lights go off. The monkey has to learn to press the odd one in order to get a pellet of food. The equipment fits on the front of the cage within easy [Music] reach. On this trial, she presses the right panel and gets the food. A recording is made of each trial as the monkey gradually learns this new way of getting something to eat. Large numbers of trials made at different stages in the learning period are averaged in a computer. Averaged records taken early in the learning period look like this. The tone goes on. The symbols appear. She makes a choice. There is very little change in resistance to the current. But compare the change in resistance after the monkey has stored the new information. where a change in resistance occurs as learning progresses. It strongly suggests that the learning causes a chemical change in the tissue. This opens up fascinating new questions. What is the nature of the chemical change? And another fascinating question. Many impulses pass through the neurons of an untrained monkey without producing these changes in resistance. Why is there a change in resistance only when the neurons are firing as a result of the new learning? By basic research such as this, we are exploring bit by bit the mysteries of the nervous system. There is much that we do not understand. But already there are many ways in which we are applying new knowledge. Medical scientists can now implant electrodes in human brains for the purpose of studying diseases of the brain. At the same time, they are using the opportunity to do basic research on its electrical activity. Recordings are made on an EEG. The brain waves are also recorded on magnetic tape for analysis by a computer. By these studies, the doctor was able to decide that the patient could be helped by surgery. In this case, the surgeon knew just what part of the brain was diseased and had to be removed. He also knew that he wouldn't have to remove so much that the patient would suffer ill effects. Gradually we are getting some understanding of this mysterious part of our bodies. But the major questions remain for new generations to solve. What is memory? What is learning consciousness sleep? What causes crippling disease? Why do we behave as we do? We are studying the physiology of the nervous system, its chemistry, its electrical activity, its abnormalities, its relation to the psychology of human [Music] behavior. Here is a new world to conquer, the great ocean of truth. Heat. Heat. Heat. [Music]