The Nervous System. Behavior

The neuron theory could be applied usefully to the problem of animal behavior. As early as 1730, Stephen Hales, found that if he decapitated a frog, it would still kick its leg if its skin were pricked. Here a body reacted mechanically without the aid of the brain. This initiated a study of the more or less automatic "reflex action," where a response follows hard upon a stimulus, according to a set pattern and without interference of the will.

Even the human being is not free of such automatic action. A blow just beneath the kneecap will produce the familiar knee jerk. If one's hand comes casually into contact with a hot object, it is snatched away at once, even before one becomes consciously aware that the object is hot.

The English physiologist, Charles Scott Sherrington (1861-1952), studied reflex action and founded neurophysiology, as Golgi and his stain had earlier founded neuroanatomy. Sherrington demonstrated the existence of the "reflex arc," a complex of at least two, and often more than two, neurons. Some sense impression at one place sent a nerve impulse along one neuron, then over a synapse (Sherrington invented the word), then, via a returning neuron, back to another place, where it stimulated muscle action or, perhaps, gland secretion. The fact that there might be one or more intermediate neurons between the first and last did not affect the principle.

It could seem that synapses were so arranged that some were crossed by the impulse more easily than others. Thus, there might be particular "pathways" that were easily traveled among the interlacing cobweb of neurons that made up the nervous system.

It could further be supposed that one pathway might open the way for another; that, in other words, the response of one reflex action might act as the stimulus for a second which would produce a new response acting as a stimulus for a third and so on. A whole battery of reflexes might then make up the more-or-less complex behavior pattern we call an "instinct."

A relatively small and simple organism like an insect could be very little more than a bundle of instincts. Since the "nerve pathways" can be conceived of, easily enough, as being inherited, one can understand that instincts are inherited and are present from birth. Thus, a spider can spin a web perfectly, even if it has never seen a web being spun; and each species of spider will spin its own variety of web.

Mammals (and man in particular) are relatively poor in instincts but are capable of learning, that is, of evolving new behavior patterns on the basis of experience. Even though the systematic study of such behavior in terms of the neuron theory may be difficult, it is possible to analyze behavior in a purely empirical fashion. Throughout history, intelligent men have learned to calculate how human beings would react under particular circumstances and this ability has made them successful leaders of men.

The application of quantitative measurement to the human mind, however (at least to its ability to sense the environment), begins with the German physiologist, Ernst Heinrich Weber (1795-1878). In the 1830s, he found that the size of the difference between two sensations of the same kind depended on the logarithm of the intensity of the sensations.

Just as in lighting a room, if we begin with a room lit by one candle, a second equal candle is sensed as brightening the room by an amount we call x. Further brightening’s of that degree are not produced by single additional candles but by larger and larger sets of candles. First one additional candle will suffice to brighten the room by x, then two more candles will be required for a further by x, then four more, then eight more, and so on. This rule was popularized in i860 by the German physicist, Gustav Theodor Fechner (1801-87), and is sometimes called the "Weber-Fechner law" in consequence. This initiated psychophysics, the quantitative study of sensation.

The study of behavior generally (psychology) is less easily reduced to mathematics, but it can be made experimental. The founder of this approach was the German physiologist, Wilhelm Wundt (1832-1920), who set up the first laboratory dedicated to experimental psychology in 1879. Out of his work arose patterns of experimentation which involved setting rats to solving mazes and chimpanzees to reasoning out methods for reaching bananas. This was applied to human beings, too, and in fact the asking of questions and setting of problems was used in the attempted measurement of human intelligence. The French psychologist, Alfred Binet (1857-1911), published his first IQ (intelligence quotient) tests in 1905.

More fundamental studies, relating behavior more directly to the nervous system, were made by the Russian physiologist, Ivan Petrovich Pavlov (1849-1936). In the earlier portion of his career, he was interested in the nerve control of the secretion of digestive juices. With the turn of the century, however, he began to study reflexes.

A hungry dog which is shown food will salivate. This is a reasonable reflex, for saliva is needed for the lubrication and digestion of food. If a bell is made to ring every time the dog is shown food, it will associate the sound of the bell with the sight of food. Eventually, it will salivate as soon as it hears the sound of the bell, even though it sees no food. This is a "conditioned reflex." Pavlov was able to show that all sorts of reflexes could be set up in this fashion.

A school of psychology, "behaviorism," grew up which maintained that all learning was a matter of the development of conditioned reflexes and of new hookups, so to speak, of the nerve network. One related the appearance of the print patterned "chair", with the sound pattern produced in pronouncing the word, and with the actual object in which one sits, until finally the mere sight of "chair" induces the thought of the object at once. The outstanding exponents of this school at its extreme were two American psychologists, John Broadus Watson (1878-1958)and, later,Burrhus Frederic Skinner (1904-).

Behaviorism is an extremely mechanistic view of psychology, and reduces all phases of the mind to the physical pattern of a complex nerve network. However, the current feeling is that this is too simple an interpretation. If the mind is to be interpreted mechanistically, it must be done in more subtle and sophisticated fashion.