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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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