The Mechanism Of The Influence Of Mind On Body

The question as to how mind influences body, and body mind, has always

proved a riddle to all but those with a special theory in the matter.

The facts of the mutual influence of mind on body are so obtruded on

observation that they could never be missed, but it is quite another

thing to reach a satisfactory explanation of them. How the will

initiates motion continues in spite of all our advance in psychology,

to be as much a mystery as ever. Just how sensation is transformed

into ideas is a parallel mystery. Since the mind is able to influence

motion, it is not surprising that it should be capable of modifying

secretion or inhibiting other kinds of functions. Any of these various

activities is scarcely more mysterious than the other. Since the

transformation of sensation into thought takes place, it is

comparatively easy to conclude that the mental processes are able to

exclude, or to some extent inhibit, sensation. All these activities

have actually been observed. How does this mutual influence of mind on

body take place? What principles underlie it?

At present, it would be futile to hope to outline the absolute

principles on which the mechanism of mental influence or suggestion

depends, but we can discuss recent explanations that have been

offered, and this will help us to understand, not the mystery itself,

but just where the mystery lies and what the physical mechanism

connected with it is.


of the methods of Weigert and Golgi--after Andriezen). c, z.,

clear zone free from nerve fibers; M.P., Exner's plexus in the

molecular layer; A. str., ambiguous cell stratum; Subm, P.,

sub-molecular plexus; Gt. P. P., great pyramidal plexus; Pol.

P., polymorphic plexus; W., white matter. (Barker.) ]

These explanations are as yet only theoretic, but theories have often

helped students in science to make their thoughts more concrete and

their investigations more practical. It would be a mistake to conclude

that because some of the theories advanced are very plausible, we

have, therefore, reached definite truth with regard to the mechanics

of the brain that underlie suggestion and mental influence.

Brain Complexity.--The most interesting feature of the discoveries in

brain anatomy during the past generation, has been that the central

nervous system is of even greater complexity than had been thought.

Because of this, these new discoveries, instead of solving the

biological mystery they subtend, or even helping very much to solve

it, have made it still harder to understand just how we succeed in

controlling and directing this immensely complex machine, of whose

details we are utterly unconscious, yet which we learn to use with

such discriminating nicety of adjustment and accomplishment. The

discoveries of Golgi and of Ramon y Cajal show us that the brain

consists of nerve cells with a number of ramifying fibers connecting

each cell and each group of cells with other simple and compound

elements of the brain, and sending down connecting fibers to every

organ and every part of the body. Dr. Ford Robertson calculates that

in an average human brain there are at least three billions of cells.

Without knowing anything of their existence, much less anything of the

infinite detail of their structure and mode of operation, we have

learned to use these for many purposes.


neighborhood of the calcarine fissure. A. plexiform layer; B, layer

of the little pyramid; C, layer of the medium-sized pyramid; a,

descending axis cylinders; b, ascending or centripetal collaterals;

c, stems of the giant pyramidal cells. (Ramon y Cajal.)

(This and the next three illustrations illustrate the complexity of

the central nervous system as observed in the very young child where

the development does not as yet obscure the interesting details of

dentritic branching. They serve to emphasize the much more

pronounced condition which develops in the adult.)]

Nerve Impulses.--We do not know even how nerve impulses travel.

Probably they do so by a mode of vibration, just as heat and light and

electricity are transmitted as modes of motion. The similarity that

used to be thought to exist between the transmission of nerve impulses

and of electrical energy is now known definitely to be only an

analogy, and not to represent anything closer. Waves of nervous energy

travel at a different rate of speed from electrical waves, and there

are other notable differences. Such phases as molecular action, or

motion, or vibration are only cloaks for our ignorance, A generation

ago Huxley declared that "the forces exerted by living matter are

either identical with those existing in the inorganic world or are

convertible into them." He instanced nervous energy as the most

recondite of all, and yet as being in some way or other

associated with the electrical processes of living beings. As Prof,

Forel said in his "Hygiene of the Nerves," "the neurokym cannot be a

simple physical wave, such as electricity, light or sound; if it were

its exceedingly fine weak waves would soon exhaust themselves without

causing the tremendous discharges which they actually call forth in

the brain."

Law of Avalanche.--How great is the power of the nervous system or the

energy of it that may be set loose by some very simple reflex, as

suggested by Forel, is illustrated by what Ramon y Cajal calls the Law

of Avalanche. A single peripheral nerve ending is represented in many

different portions of the brain. An ocular nerve ending, for instance,

probably has direct connection with four or more portions of each

hemisphere. Each of these portions of the brain has association fibers

connecting it with other parts and so the stirring of a single nerve

ending may disturb many thousands, perhaps hundreds of thousands, of

brain cells; at least it affects them in some way or other. The older

psychologists used to insist on the similarity, or analogy, between

the cosmos ol the universe and the microcosmos that man is. The

English poet of the nineteenth century told us that there is no

moving of a flower without the stirring of a star, so intimately

connected by the laws of gravitation is the universe. In the microcosm

something of this same thing is true and a titillation of even the

most trivial nerve ending may produce, in Ramon y Cajal's phrase, "an

avalanche" of cell disturbances in the central nervous system which

may seriously disturb the whole system.

What is thus true for the brain is true, also, for the cord, and the

complexity of spinal cells needs to be seen to be properly realized.


CORTEX OF A CHILD FIFTEEN DAYS OLD. A and B, very thick nerve plexus

of the layer in which the little pyramids are contained; C, a plexus

containing a series of branches that is less thick and intricate; D,

small cells whose ascending axis-cylinders have resolved themselves

into a set of similar branches; E, arachnoid star cells whose axis

cylinders produce a thick plexus in the first layer; F and G, small

cells with short axis cylinders that have very few branches. (Ramon

y Cajal.)]

Psychic States.--There are a number of human states representing

extremes of sensory and intellectual conditions in man, that have

always attracted attention, and in recent years have been special

objects of investigation by physiologists. Natural sleep is one of

these; the unconsciousness of narcotism or anesthesia is another.

Hypnotism is allied to both of these, and would seem to lie on a plane

between them. Then there are various states of exaltation in which

sensations fail to produce their usual effect. Those escaping

from a fire, or passing through a severe panic of any kind may sustain

all manner of injuries without being aware of them. Martyrs, for all

manner of causes, are able to withstand suffering with such

equanimity, and sometimes even joy, that it is evident that they

cannot feel, as would people under ordinary conditions, the pain that

is being inflicted on them.

In the midst of intense mental preoccupation one may hold so cramped a

position as would be quite impossible for the same length of time with

the faculties normally engaged. There are pathological conditions,

like hysteria, in which the pain and fatigue sense may, for a time at

least, be quite in abeyance.

Neurons.--With the advance in our knowledge of brain anatomy, various

explanations for these curious conditions have been suggested. The

discovery that the central nervous system is composed of a large

number of separate units, and not of a feltwork of continuous fibers

with cells here and there, revolutionized all previous attempts at

explanation of these conditions. We know now that it is not fibers but

cells that are the most important components of the brain and

spinal-cord substance, and that, indeed, the fibers are only

prolongations of cells. The central nervous system is made up of nerve

cells with various appendages, and each one of these cells and its

appendages is called a neuron. These appendages are of two kinds, one

the axon, the long conducting fiber which transmits the nerve force of

the cell, the other the dendrons or connecting elements by which the

cell is linked with the axon of another cell. The contact of the axon

of one neuron with the dendrons of another is called a synapse. Each

neuron does not extend to and from the brain and the periphery, but

series of neurons connect the surface of the body with the brain.

There is usually a group of neurons in the path from the surface to

the brain cortex. The peripheral neuron for sensation runs from the

surface of the body to the spinal cord, while for motion it runs in

the opposite direction. There is a secondary neuron in each chain that

runs up or down the spinal cord to and from the base of the brain. A

third--sometimes, perhaps, a fourth--neuron connects in the two

directions, afferent and efferent, the cortex and the base of the


Neuronic Movement.--Duval, the French anatomist and histologist,

suggested the possibility of voluntary and involuntary movement in the

neurons or nerve cells themselves, thus making and breaking


According to his suggestion, sleep would be due to a separation of the

neurons that run from the surface of the body to the brain cortex,

because the various neurons had become too tired for further function.

As a consequence of fatigue, their terminal filaments would fall away

from one another, external sensations would no longer be communicated

to the brain, because the peripheral neuron was not connected with the

next in the chain. As a further result, the brain, undisturbed by

sensations, would be left at rest so far as the body was concerned.

Within the brain certain connections through which flow thoughts that

would keep us awake, are also supposed on this theory to be broken,

and consequently all the nerve cells have a chance to rest, except, of

course, those concerned with such very vital functions as heart

movement, respiration and peristalsis.

Somehow, these vital neurons obtain their rest in the intervals

between the impulses which they send down, just as cardiac cells do

between heart beats.

Neurons in Psychic States.--This same explanation would serve for

narcosis, that is, for anesthesia, due to chloroform or ether, or any

other drug. As a consequence of the effect of the narcotic upon the

central neuron, they are brought into a condition resembling fatigue,

at least to the extent of breaking their connections with other

neurons so long as they are under the influence of the drug. While

sensory nerves at the periphery, then, are being stimulated by the

cutting of tissues to which they are attached, the message from them

does not reach the brain because of a disturbance of the connections

in the chain of neurons. Drunkenness illustrates the same phenomenon

in a less degree. The effect of the intoxicant upon the central

neurons disturbs sensation because it makes the connection much less

complete than before, and so it is easy to understand the familiar

occurrence of even severe injuries to drunken men without their being

aware of them, or at least without their suffering nearly so much as

would be the case if they were not intoxicated.

Hypnotism.--The same theory would also hold for the phenomena

observed in hypnotism. After all, the best explanation of hypnotism

that we have is that there is a turning inward of the patient's

attention, so that only those sensations are allowed to reach the

brain to which mental attention has already been called by suggestion.

Hypnotism usually begins with a certain fatigue of peripheral neurons

until these do not act normally, and then the cerebral neurons become,

as it were, short-circuited on themselves with a consequent internal

concentration of attention. The anesthesia so often noted in hypnotic

or hysterical states is explained by the same theory. For the time

being, at least, the connection between the peripheral neurons and the

central neurons is broken or but imperfectly made, and conduction does

not take place, or is hampered. There may be loss of motion as well as

of sensation, or of motion without sensation. In all these cases, the

discontinuity of the nervous system enables us to understand more

readily the mechanism by which these curious phenomena occur.

Exaltation or intense interest or profound preoccupation may so

concentrate nervous energy within the nerve centers themselves as to

inhibit the flow of sensory impulses from without and thus enable

people to stand pain and fatigue that would otherwise seem quite


Unconsciousness.--The unconsciousness due to apoplexy, or to a blow

on the head, would be comparatively easy of explanation on the same

theory. The hemorrhage would actually push certain neurons apart

within the skull, or the intracranial pressure produced by it would

keep them from making proper connections. A blow on the head may

readily be supposed to jar neuronic terminal filaments so severely

that it would be some time before connections could be made, and the

injury might be serious enough to prevent certain cells from ever

again coming in contact in such a way as to allow the passage of nerve

impulses from one to the other. Concussion of the brain would, on this

theory, mean that neurons were so shaken apart as to produce some

confusion in their terminal filaments and consequent serious

disturbances of consciousness, if not its complete loss, and

corresponding disturbance of the power to move. In a word, this theory

would seem to afford a reasonably satisfactory explanation for most of

the extraordinary phenomena of mental life and, therefore, might also

be expected to be applicable to the ordinary phenomena, though these

are so elusive that it is difficult to satisfactorily apply theories

to them.

Tired States.--When fatigued, it becomes extremely difficult for us

to follow a train of thought, especially if it is somewhat intricate.

It becomes easy to forget things, even such as under ordinary

circumstances would be readily remembered. Names are much more likely

to be forgotten. Facts and, above all, dates, refuse to come as they

do under normal conditions. Efforts in the direction of recalling

details are eminently unsatisfactory. The command goes forth, but

there is evidently hesitation about obedience. Other thoughts

intrude themselves. Ideas come unbidden. The connection of thought is

readily broken, and is hard to get at again. There may have been very

little mental work, but somehow the fatigue of the general physical

system is reflected through our central nervous system on the mind as

well as the body. The early morning hours are the best for mental

work, not, it seems, because the mind is fresher after its rest, but

rather because the physical factors that are important for mental

action are in good condition. Later they become disturbed by the

fatigues of the day. The delicate cells of the brain become fatigued

by sympathy with the somatic cells and it is harder to secure those

nervous connections necessary for thought.

Voluntary Neuron Motion.--This theory of Duval's supposes that to

some extent the neurons or nerve cells are possessed of voluntary

movement. At least during certain states of the mind, they are moved

and seem to have an inherent, if not quite voluntary, power of

motion. There are many objections urged against the theory because of

this neuronic motion. It has been said that the movement of neurons

has been observed in certain of the Medusae. The observation has

been doubted and it lacks confirmation. In higher animals, of course,

the observation is impossible because an investigation of the nervous

system for this purpose would necessarily bring about the death of the

animal and the cessation of spontaneous mobility. Whether it occurs or

not, therefore, is a theoretic problem. So many objections tell

against Duval's theory that it is now only discussed because of its

subjective value.

Neuroglia Theory.--Ramon y Cajal elaborated a second theory of

explanation for the mechanism of the nervous system that has seemed to

many authorities in brain physiology much more satisfactory than

Duval's theory of the actual motion of the neurons themselves. The

Spanish nervous histologist had made a special study of the neuroglia

or connective tissue cells in the central nervous system. These are

very small in size but very numerous. Ramon y Cajal suggested that it

was because the terminal filaments of these neuroglia cells inserted

themselves between the neuronic filaments, thus insulating one from

another, somewhat as if an insulating plug were inserted between two

portions of an electric circuit, that the interruption of nervous

currents took place. This explanation is free from many of the

objections urged against Duval's theory.

The small size of the neuroglia cells makes it easy to understand how

movement may take place in them sufficient to bring about separation

of neurons. It would not be surprising if they should be more or less

actively contractile. Whenever they contract, neuronic filaments which

they have been holding apart, come together so as to permit the

passage of nervous impulses, if any are flowing at the time. When the

neuroglia cells become fatigued or seriously disturbed, they refuse

any longer to obey the will in any way, or at least gradually get

beyond control, and in their relaxation becoming prolonged, push

neurons apart. When a man is very tired it gradually becomes

impossible for him to keep awake. This is partly because poisons,

produced in the course of fatigue, exhaust the vitality of the

neuroglia cells and also of the neurons, so that less energy is

required to push these latter apart.

It is easy to understand that the neuroglia cells might well become

affected by the various narcotics and intoxicants in such a way as to

produce the phenomena of anesthesia and drunkenness. The rapid

recovery from anesthetics seems to indicate that it is not neurons, or

essential nerve cells, that are so deeply affected, but some

extraneous, and less important, mechanism within the brain. The

neuroglia theory explains this very well and does away with the

difficulty. Certain curious phenomena of hysteria are easily explained

on this theory. When there is anesthesia in a member because of

hysteria, this anesthesia does not follow the distribution of certain

nerves, but is limited by a line in the shape of a cuff drawn round

the limb. This indicates that the trouble is not peripheral but

central, and that owing to psychic disturbance, all the neurons that

receive sensory impulses from a particular portion of the body are so

affected by a psychic condition that they are no longer capable of

receiving impulses from the periphery. The neuroglia cells in a

particular area have passed from the control of the will and, relaxing

themselves, have inserted their processes between the terminal

filaments of neurons, thus preventing conduction.

Varieties of Neuroglia.--The connective tissue cells are of many

kinds, each probably exercising a special function. Ramon y Cajal has

described and pictured a special kind of neuroglia cells for the gray

and another for the white matter. In his description of these cells he

has pointed out many interesting diversities of form, and probably

also of function. He has also described particularly a special form of

neuroglia cells which lie close to the blood vessels. These he calls

perivascular cells, and they seem to have an important function in

regulating the amount of blood that goes to a particular part of the

brain. He has written so clearly and yet so concisely with regard to

these that it seems better to cite his own words: [Footnote 15]

[Footnote 15: This article is a translation made by the author shortly

after a visit to Ramon y Cajal in Madrid, in 1900. See International

Clinics, Phila., Vol. II Series Eleventh.]

Under the term neuroglia are included at least three kinds of

cells,--those of the white brain substance, those of the gray

substance, and the perivascular cells, which have been described by

Golgi. The neuroglia cells of the white brain material are easily

recognizable, being large and with rather prominent, smooth, and

sharply outlined processes. As my brother seems to have shown, their

object appears to be to furnish an insulating, or, at least, a badly

conducting, substance to serve as an interrupter of nerve-currents.

They certainly do not represent interstices of true nerve substance

through which lymphatic fluid can conveniently find its way.

The neuroglia cells of the gray matter present a very special and

highly characteristic appearance. They are of manifold form,--at

times star-shaped, at times like a comet drawn out in length.

These are the tall cells of von Retzius. They have very numerous

prolongations, with a large number of short branched collaterals

which give the whole cell the appearance of having feathers

projecting from its periphery. These cells have been observed in two

different conditions. One is that of relaxation, and the picture is

that given above. The other is that of contraction, during which the

cell body has more protoplasm in it, and the processes become

shorter and thicker, and some of the secondary branches disappear

entirely. These cells resemble, in certain ways at least, the

pigment cells which occur in the skin of some animals. By means of

their contractility, these pigment cells can stretch out their

processes while in a state of contraction. It must be remembered

that this form of neuroglia cells is most abundantly present in

those parts of the brain in which it might be expected that a number

of nerve currents would frequently come together. They occur, for

example, with special frequency in the molecular layer of the

cerebral cortex, where the bundle of pyramidal fibers, with their

immense number of terminal nerve-endings, come in contact with one


The third form of neuroglia cells consists of those known as the

perivascular cells. They are found only in the neighborhood of the

capillaries of the gray matter and they send one or more firm

prolongations to the outer surface of the endothelium of the blood


These processes are inserted in the walls of the blood vessels.

Every capillary has thousands of these little pseudopod

prolongations, and from the vessel the cell reaches out in a number

of directions. The object of these cells undoubtedly is by

contraction of the prolongations to bring about local dilatation of

the blood vessels. This dilatation of the blood vessels causes

greater or less intensity of the psychical processes in certain

parts of the brain, because of the greater or less congestion of the

circulation in a part which it produces.

With the exception of these last cells the object of the neuroglia

cells is to insulate nerve fibrils and cells from one another. When

the cells are relaxed, the passage of a nerve current is either

entirely prevented or rendered much less easy than before. It is in

this way that the true nature of intellectual rest is explained.

Sleep--not only natural sleep, but also artificial narcosis, such as

is produced by narcotics, hypnotics or hypnotization--is evidently

the result of the same conditions.

During the state of contraction the pseudopod of the neuroglia cells

are drawn in; that is to say, the protoplasm of the cells absorbs

the processes, and so the true nerve cells and nerve fibrils which

were separated from each other by the interposition of neuroglia

come into contact. By this mechanism the brain passes from the

condition of rest into one of activity. These neuroglia contractions

may, particularly in certain parts of the brain, occur

automatically. Often, however, they are produced by the action of

the will, which, in this manner is able to influence the

definite groups of neuroglia cells. As the result of this influence

of the will the association of intellectual operations can be guided

in various directions. The unusual course that the association of

ideas sometimes takes, the flow of words and of thoughts at certain

moments, the passing difficulty of speech, the recurrence of

tormenting thoughts, the disappearance of expressions or ideas from

the memory, even the increase of mental activity and of every kind

of motor reaction as well as many other phenomena of intellection,

can be satisfactorily explained on this hypothesis. It is only

necessary to suppose that in certain parts of the brain the

neuroglia cells are at rest, while at other parts they are in a

condition of active contraction.

To put it all in a few words, the neuroglia cells of the gray

substance of the brain represent an insulating and switching

apparatus for nerve currents. They are an insulation apparatus when

in a state of contraction, a switching and insulating apparatus when

in a state of rest. It is to be remarked, then, that according to

this theory the contraction of brain cells does not take place, as

in Duval's theory, during intellectual rest, but, on the contrary,

during the state of activity of the cerebral cortex. It is much more

probable that the action of cells coincides with the active stage of

intellection than that brain cellular activity--that is,

contraction--should correspond with psychic rest.

The application of some of these theories enables us to understand

just how short-circuiting may come about, how many of the curious

phenomena of memory happen, and what are the effects, as well as the

causes, of attention and distraction of attention and of diversion of

mind. It is particularly the latter portion of Ramon y Cajal's theory,

with regard to attention and the more or less voluntary though

unconscious and usually indeliberate control of blood supply to

various portions of the brain, that is of special interest. If the

neuroglia cells, whose end plates are attached to blood-vessel walls,

become over-contracted or lose their power of relaxation or of

contraction, many of the curious phenomena of over-tiredness in

neurotic conditions, and the lack of the power of concentration, and

sufficient attention to things, can be readily understood. In a word,

the theory enables us to translate many expressions that are vague and

indefinite, from terms of mind into terms of the physical basis of

mind--the anatomy and physiology of the brain.

While I have dwelt on Ramon y Cajal's theory, because for years it has

been familiar, of course I must re-echo his own warning that it is,

after all, only a theory. It presupposes an active interposition of

the glia cells between the axon of one neuron and the dendrons of

another. This cannot be demonstrated. A third theory of mental

operations, then, has been suggested, and the English school, so ably

led by Sherrington ("Integrative Action of the Nervous System,"

London, 1903) and McDougal ("Synapse Theory of Fatigue," Brain,

1910) has deservedly attracted wide attention. They contend that all

the phenomena can be more simply explained without postulating the

movement required for the Duval Theory or the glial activity of Ramon

y Cajal's hypothesis. They consider that each nerve cell has, as it

were, a certain potential energy which it sends forth in nerve

impulses. These are transferred from neuron to neuron through the

synapse. If what we might call, to borrow a figure from electricity,

the voltage of the cell impulse be sufficient to overcome the

resistance at the synapse, the impulse passes from neuron to neuron.

In fatigue the potential energy of the cell is gradually dissipated.

The impulses become feebler till they cease to pass. This occurs in

the state we usually experience as tiredness and in analogous states

such as sleep, unconsciousness, narcosis and the like. Obviously this

theory can be elaborated and applied parallel with the neuroglia

theory except that here we are substituting synapse resistance for the

hypothetical, undemonstrated action of the glial cells. But, as the

latter seems a simpler process upon which to explain the various

phenomena, especially to those not familiar with very recent

developments in nervous histology and studies in nervous mechanism,

and as it merely involves a question of the nature of the resistance

and not of its site, I have used it for explanatory purposes without

advocating either theory in the present state of our knowledge.

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