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

of the nociceptors for pain is not the only means by which a discharge of nervous energy is caused.

Nervous energy may be discharged also by adequate stimulation of the various ticklish regions of the body; the entire skin surface of the body contains delicate ticklish receptors.

These receptors are closely related to the nociceptors for pain, and their adequate stimulation by an insect-like touch causes a discharge of energy,—a nerve-muscular reaction,—

resembling that developed for the purpose of brushing off insects.

This reflex is similar to the scratch reflex in the dog.

The discharge of energy is almost wholly independent of the will and is a self-protective action in the same sense as is the response to pain stimuli. The ear in man and in animals is acutely ticklish, the adequate stimulus being any foreign body, especially a buzzing, insect-like contact. The discharge of nervous energy in horses and in cattle on adequate stimulation of the ticklish receptors of the ear is so extraordinary that in the course of evolution it must have been of great importance to the safety of the animal.

A similar ticklish zone guards the nasal chambers, the discharge of energy here taking a form which effectively dislodges the foreign body.

The larynx is exquisitely ticklish, and, in response to any adequate stimulus, energy is discharged in the production of a vigorous cough.

The mouth and pharynx have active receptors which cause the rejection of noxious substances. The conjunctival reflex, though not classed as ticklish, is a most efficient self-protective reflex.

I assume that there is no doubt as to the relation between the adequate stimuli and the nerve-muscular response of the various ticklish receptors of the surface of the skin, of the ear, the nose, the eye, and the larynx. These mechanisms were developed by natural selection as protective measures against the intrusion of insects and foreign bodies into regions of great importance.

The discharge of energy in these instances is in accordance with the laws of inheritance and association. The other ticklish points which are capable of discharging vast amounts of energy are the lateral chest-wall, the abdomen, the loins, the neck, and the soles of the feet. The type of adequate stimuli of the soles of the feet, the distribution of the ticklish points upon them, and the associated response, leave no doubt that these ticklish points were long ago established as a means of protection from injury.

Under present conditions they are of little value to man.

 

The adequate stimulus for the ticklish points of the ribs, the loins, the abdomen, and the neck is deep isolated pressure, probably the most adequate being pressure by a tooth-shaped body.

The response to tickling in these regions is actively and obviously self-defensive. The horse discharges energy in the form of a kick; the dog wriggles and makes a counter-bite; the man makes efforts at defense and escape.

 

There is strong evidence that the deep ticklish points of the body were developed through vast periods of fighting with teeth and claws (Fig. 9). Even puppies at play bite each other in their ticklish points and thus give a recapitulation of their ancestral battles and of the real battles to come (Fig. 10). The mere fact that animals fight effectively in the dark and always according to the habit of their species supports the belief that the fighting of animals is not an intellectual but a reflex process. There are no rules which govern the conduct of a fight between animals. The events follow each other with such kaleidoscopic rapidity that the process is but a series of automatic stimulations and physiologic reactions.

Whatever their significance, therefore, it is certain that man did not come either accidentally or without purpose into possession of the deep ticklish regions of his chest and abdomen.

Should any one doubt the vast power that adequate stimulation of these regions possesses in causing the discharge of energy, let him be bound hand and foot and vigorously tickled for an hour.

What would happen? He would be as completely exhausted as though he had experienced a major surgical operation or had run a Marathon race.

 

A close analogy to the reflex process in the fighting of animals is shown in the role played by the sexual receptors in conjugation.

Adequate stimulation of either of these two distinct groups of receptors, the sexual and the noci, causes specific behavior—

the one toward embrace, the other toward repulsion. Again, one of the most peremptory causes of the discharge of energy is that due to an attempt to obstruct forcibly the mouth and the nose so that asphyxia is threatened. Under such conditions neither friend nor foe is trusted, and a desperate struggle for air ensues.

It will be readily granted that the reactions to prevent suffocation were established for the purpose of self-preservation, but the discharge of nerve-muscular energy to this particular end is no more specific and no more shows adaptive qualities than do the preceding examples.

Even the proposal to bind one down hand and foot excites resentment, a feeling originally suggested by the need for self-preservation.

No patient views with equanimity the application of shackles as a preparation for anesthesia.

 

We have now considered some of the causes of those discharges of nervous energy which result from various types of harmful physical contact, and have referred to the analogous, though antithetical, response to the stimulation of the sexual receptors.

The response to the adequate stimuli of each of the several receptors is a discharge of nerve-muscular energy of a specific type; that is, there is one type of response for the ear, one for the larynx, one for the pharynx, another for the nose, another for the eye, another for the deep ticklish points of the chest and the abdomen, quite another for the delicate tickling of the skin, and still another type of response to sexual stimuli.

 

According to Sherrington, a given receptor has a low threshold for only one, its own specific stimulus, and a high threshold for all others; that is, the doors that guard the nerve-paths to the brain are opened only when the proper password is received.

According to Sherrington’s law, the individual as a whole responds to but one stimulus at a time, that is, only one stimulus occupies the nerve-paths which carry the impulses as a result of which acts are performed, i. e., the final common path.

As soon as a stronger stimulus reaches the brain it dispossesses whatever other stimulus is then occupying the final common path—

the path of action. The various receptors have a definite order of precedence over each other (Sherrington). For example, the impulse from the delicate ticklish points of the skin, whose adequate stimulus is an insect-like contact, could not successfully compete for the final common path with the stimulus of a nociceptor.

The stimulus of a fly on the nose would be at once superseded by the crushing of a finger. In quick succession do the various receptors (Sherrington) occupy the final common path, but each stimulus is for the time the sole possessor, hence the nervous system is integrated (connected) to act as a whole. Each individual at every moment of life has a limited amount of dischargeable nervous energy.

This energy is at the disposal of any stimulus that obtains possession of the final common path, and results in the performance of an act.

Each discharge of energy is subtracted from the sum total of stored energy and, whether the subtractions are made by the excitation of nociceptors by trauma, by tickling, by fighting, by fear, by flight, or by the excitation of sexual receptors, by any of these singly or in combination with others, the sum total of the expenditure of energy, if large enough, produces exhaustion.

Apparently there is no distinction between that state of exhaustion which is due to the discharge of nervous energy in response to trauma and that due to other causes. The manner of the discharge of energy is specific for each type of stimulation.

On this conception, traumatic shock takes its place as a natural phenomenon and is divested of its mask of mystery.

 

The Discharge of Energy through Stimulation of the Distance Receptors, or through Representation of Injury (Psychic) We will now turn from the discussion of the discharge of nervous energy by mechanical stimuli to the discharge of energy through mental perception.

Phylogenetic association may result from stimulation of the distance receptors through sight, hearing, smell, or by a representation of physical experiences, as well as from physical contact.

The effect upon the organism of the representation of injury or of the perception of danger through the distance receptors is designated FEAR. Fear is as widely distributed in nature as is its cause, that is, fear is as widely distributed as injury. Animals under the stimulus of fear, according to W. T. Hornaday, not only may exhibit preternatural strength, but also may show strategy of the highest order, a strategy not seen under the influence of a lesser stimulus.

In some animals fear is so intense that it defeats escape; this is especially true in the case of birds in the presence of snakes.

The power of flight has endowed the bird with an easy means of escape from snakes, especially when the encounter is in the tops of trees.

Here the snake must move cautiously, else he will lose his equilibrium; his method of attack is by stealth. When the snake has stalked its prey, the bird is often so overcome by fear that it cannot fly and so becomes an easy victim (Fig. 11). The phenomena of fear are described by Darwin as follows:

 

“Fear is often preceded by astonishment, and is so near akin to it that both lead to the senses of sight and hearing being instantly aroused.

In both cases the eyes and mouth are widely opened and the eyebrows raised. The frightened man at first stands like a statue, motionless and breathless, or crouches down as if instinctively to escape observation. The heart beats quickly and violently, so that it palpitates or knocks against the ribs. * That the skin is much affected under the sense of great fear we see in the marvelous and inexplicable manner in which perspiration immediately exudes from it.

This exudation is all the more remarkable as the surface is then cold, and hence the term, `a cold sweat’; whereas the sudorific glands are properly excited into action when the surface is heated.

The hairs also on the skin stand erect, and the superficial muscles shiver. In connection with the disturbed action of the heart, the breathing is hurried. The salivary glands act imperfectly; the mouth becomes dry, and is often opened and shut. I have also noticed that under slight fear there is a strong tendency to yawn.

One of the best-marked symptoms is the trembling of all the muscles of the body; and this is often first seen in the lips.

From this cause, and from the dryness of the mouth, the voice becomes husky and indistinct, or may altogether fail.

* As fear increases into agony of terror, we behold, as under all violent emotions, diversified results. The heart beats wildly, or may fail to act and faintness ensues; there is death-like pallor; the breathing is labored; the wings of the nostrils are widely dilated; `there is a gasping and convulsive motion of the lips, a tremor on the hollow cheek, a gulping and catching of the throat’; the uncovered and protruding eyeballs are fixed on the object of terror; or they may roll restlessly from side to side. * The pupils are said to be enormously dilated. All the muscles of the body may become rigid, or may be thrown into convulsive movements.

The hands are alternately clenched and opened, often