The Origin and Nature of Emotions - George W. Crile (books to read to improve english txt) 📗

nervous system was primarily to secure some form of motor activity, first as a means of securing food, and later as a means of escaping from enemies and to promote procreation.

Activities for the preservation of the individual and of the species were and are the only purposes for which the body energy is expended.

The central nervous system hag accordingly been developed for the purpose of securing such motor activities as will best adapt the individuals of a species for their self-preservative conflict with environment.

 

It is easy to appreciate that the simplest expressions of nerve response—

the reflexes—are motor in character, but it is difficult to understand how such intangible reactions as love, hate, poetic fancy, or moral inhibition can be also the result of the adaptation to environment of a distinctively motor mechanism. We expect, however, to prove that so-called “psychic” states as well as the reflexes are products of adaptation; that they occur automatically in response to adequate stimuli in the environment; that, like the reflexes, they are expressions of motor activity, which, although intangible and unseen, in turn incite to activity the units of the motor mechanism of the body; and finally, that any “psychic” condition results in a definite depletion of the potential energy in the brain-cells which is proportionate to the muscular exertion of which it is the representative.

 

That this nerve mechanism may effectively carry out its twofold function, first, of self-adaptation to meet adequately the increasingly complicated stimuli of environment; and second, of adapting the motor mechanism to respond adequately to its demands, there have been implanted in the body numerous nerve ceptors—

some for the transmission of stimuli harmful to the mechanism—

nociceptors some of a beneficial character—beneceptors; and still others more highly specialized, which partake of the nature of both bene-and nociceptors—the distance ceptors, or special senses.

 

A convincing proof that environment has been the creator of man is seen in the absolute adaptation of the nociceptors as manifested in their specific response to adequate stimuli, and in their presence in only those parts of the body which throughout the history of the race have been most exposed to harmful contacts.

We find they are most numerous in the face, the neck, the abdomen, the hands, and the feet; while in the back they are few in number, and within the bony cavities they are lacking.

 

Instances of the specific responses made by the nociceptors might be multiplied indefinitely. Sneezing, for example, is a specific response made by the motor mechanism to stimulation of nociceptors in the nose, while stimulation of the larynx does not produce a sneeze, but a cough; stimulation of the nociceptors of the stomach does not produce cough, but vomiting; stimulation of the nociceptors of the intestine does not produce vomiting, but increased peristaltic action.

There are no nociceptors misplaced; none wasted; none that do not make an adequate response to adequate stimulation.

 

Another most significant proof that the environment of the past has been the creator of the man of to-day is seen in the fact that man has added to his environment certain factors to which adaptation has not as yet been made. For example, heat is a stimulus which has existed since the days of prehistoric man, while the x-ray is a discovery of to-day; to heat, the nociceptors produce an adequate response; to the x-ray there is no response.

There was no weapon in the prehistoric ages which could move at the speed of a bullet from the modern rifle, therefore, while slow penetration of the tissues produces great pain and muscular response, there is no response to the swiftly moving bullet.

 

The response to contact stimuli then depends always on the presence of nociceptors in the affected part of the body and to the type of the contact. Powerful response is made to crushing injury by environmental forces; to such injuring contacts as resemble the impacts of fighting; to such tearing injuries as resemble those made by teeth and claws (Fig. 9). On the other hand, the sharp division of tissue by cutting produces no adaptive response; indeed, one might imagine that the body could be cut to pieces by a superlatively sharp knife applied at tremendous speed without material adaptive response.

 

These examples indicate how the history of the phylogenetic experiences of the human race may be learned by a study of the position and the action of the nociceptors, just as truly as the study of the arrangement and variations in the strata of the earth’s crust discloses to us geologic history.

 

These adaptive responses to stimuli are the result of the action of the brain-cells, which are thus continually played upon by the stimuli of environment. The energy stored in the brain-cells in turn activates the various organs and parts of the body.

If the environmental impacts are repeated with such frequency that the brain-cells have no time for restoration between them, the energy of the cells becomes exhausted and a condition of shock results.

Every action of the body may thus be analyzed into a stimulation of ceptors, a consequent discharge of brain-cell energy, and a final adaptive activation of the appropriate part.

Walking, running, and their modifications constitute an adaptation of wonderful perfection, for, as Sherrington has shown, the adaptation of locomotion consists of a series of reflexes—

ceptors in the joints, in the limb, and in the foot being stimulated by variations in pressure.

 

As we have shown, the bene-and nociceptors orientate man to all forms of physical contact—the former GUIDE HIM TO the acquisition of food and to sexual contact; the latter DIRECT HIM FROM contacts of a harmful nature. The distance ceptors, on the other hand, adapt man to his distant environment by means of communication through unseen forces—ethereal vibrations produce sight; air waves produce sound; microscopic particles of matter produce smell.

The advantage of the distance ceptors is that they allow time for orientation, and because of this great advantage the majority of man’s actions are responses to their adequate stimuli.

As Sherrington has stated, the greater part of the brain has been developed by means of stimuli received through the special senses, especially through the light ceptors, the optic nerves.

 

We have just stated that by means of the distance ceptors animals and man orientate themselves to their distant environment.

As a result of the stimulation of the special senses chase and escape are effected, fight is conducted, food is secured, and mates are found.

It is obvious, therefore, that the distance ceptors are the primary cause of continuous and exhausting expenditures of energy.

On the other hand, stimuli applied to contact ceptors lead to short, quick discharges of nervous energy. The child puts his hand in the fire and there is an immediate and complete response to the injuring contact; he sees a pot of jam on the pantry shelf and a long train of continued activities are set in motion, leading to the acquisition of the desired object.

 

The contact ceptors do not at all promote the expenditure of energy in the chase or in fight, in the search for food or for mates.

Since the distance ceptors control these activities, one would expect to find that they control also those organs whose function is the production of energizing internal secretions. Over these organs—the thyroid, the adrenals, the hypophysis—the contact ceptors have no control.

Prolonged laboratory experimentation seems to prove this postulate.

According to our observations, no amount of physical trauma inflicted upon animals will cause hyperthyroidism or increased adrenalin in the blood, while fear and rage do produce hyperthyroidism and increased adrenalin (Fig. 44) (Cannon). This is a statement of far-reaching importance and is the key to an explanation of many chronic diseases—

diseases which are associated with the intense stimulation of the distance ceptors in human relations.

 

Stimuli of the contact ceptors differ from stimuli of the distance ceptors in still another important particular. The adequacy of stimuli of the contact ceptors depends upon their number and intensity, while the adequacy of the stimuli of the distance ceptors depends upon the EXPERIENCE of the species and of the individual.

That is, according to phylogeny and ontogeny this or that sound, this or that smell, this or that sight, through association recapitulates the experience of the species and of the individual—

awakens the phylogenetic and ontogenetic memory. In other words, sights, sounds, and odors are symbols which awaken phylogenetic association.

If a species has become adapted to make a specific response to a certain object, then that response will occur automatically in an individual of that species when he hears, sees, or smells that object.

Suppose, for example, that the shadow of a hawk were to fall simultaneously on the eyes of a bird, a rabbit, a cow, and a boy.

That shadow would at once activate the rabbit and the bird to an endeavor to escape, each in a specific manner according to its phylogenetic adaptation; the cow would be indifferent and neutral; while the boy, according to his personal experience or ontogeny, might remain neutral, might watch the flight of the hawk with interest or might try to shoot it.

 

Each phylogenetic and each ontogenetic experience by an indirect method develops its own mechanism of adaptation in the brain; and the brain threshold is raised or lowered to stimuli by the strength and frequency of repetition of the experience.

Thus through the innumerable symbols supplied by environment the distance ceptors drive this or that animal according to the type of brain pattern and the particular state of threshold which has been developed in that animal by its phylogenetic and ontogenetic experiences.

The brain pattern depends upon his phylogeny, the state of threshold upon his ontogeny. Each BRAIN PATTERN is created by some particular element in the environment to which an adaptation has been made for the good of the species. The *state of threshold depends upon the effect made upon the individual by his personal contacts with that particular element in his environment. The presence of that element produces in the individual an associative recall of the adaptation of his species—that is, the brain pattern developed by his phylogeny becomes energized to make a specific response.

The intensity of the response depends upon the state of threshold—

that is, upon the associative recall of the individual’s own experience—his ontogeny.

 

If the full history of the species and of the individual could be known in every detail, then every detail of that individual’s conduct in health and disease could be predicted.

Reaction to environment is the basis of conduct, of moral standards, of manners and conventions, of work and play, of love and hate, of protection and murder, of governing and being governed, in fact, of all the reactions between human beings—of the entire web of life.

To quote Sherrington once more: “Environment drives the brain, the brain drives the various organs of the body.”

 

By what means are these adaptations made? What is the mechanism through which adequate responses are made to the stimuli received by the ceptors?

We postulate that in the brain there are innumerable patterns each the mechanism for the performance of a single kind of action, and that the brain-cells supply the energy—electric or otherwise—

by which the act is performed; that the energy stored in the brain-cells is in some unknown manner released by the force which activates the brain pattern; and that through an unknown property of these brain patterns each stimulus causes such a change that the next stimulus of the same kind passes with greater facility.

 

Each separate motor action presumably has its own mechanism—

brain pattern—which is activated by but one ceptor and by that ceptor only when physical force of a certain intensity and rate of motion is applied. This is true both of the visible