Part 9

In the second place, these ideas come and go in the same fashion as do those which make up the content of the main personal consciousness; and many are constantly recurring to become coconscious memories. The same problem, of the nature of conservation, therefore confronts us with coconscious ideas in the determination of the mechanism of coconscious memory. To explain conservation through coconscious ideas is but a shifting of the problem. If a broader concept be maintained, namely, that this coconsciousness, which can be demonstrated in special conditions, is but a fraction of the sum total of coconscious ideas outside of the personal awareness, we are confronted with a concept which from its philosophical nature deals with postulates beyond experience. We can neither prove nor disprove it. There is much that can be said in its support for the deeper we dive into the subconscious regions of the mind the more extensively do we come across evidences of coconscious states underlying specific phenomena. Nevertheless, the demonstration of coconscious states in any number of specific phenomena does not touch the problem of the nature of conservation. In weighing the probability of the hypothesis on theoretical grounds it would seem, as I have already said in a preceding lecture, to be hardly conceivable that ideas that had passed out of mind, the thoughts of the moment of which we are no longer aware, can be treasured, conserved as such in a sort of psychological storehouse or reservoir of consciousness, just as if they were static or material facts. Such a conception would require that every specific state of consciousness, every idea, every thought, perception, sensation and feeling, after it had passed out of mind for the moment, should enter a great sea of ideas which would be the sum total of all our past experiences. In this sum-total millions of ideas would have to be conserved _in concrete_ form until wanted again for use by the personal consciousness of the moment. Here would be found, in what you will see at once would be a real subconscious mind beyond the content or confines of our awareness, stored up, so to speak, ready for future use, the mass of our past mental experiences. Here you would find, perhaps, the visualized idea of a seagull soaring over the waters of your beautiful bay conserved in association with the idea of the mathematical formula, a + b = c; the one having originated in a perception of the outer world through the window of your study while you were working at a lesson in algebra which gave rise to the latter. And yet conserved as ideas, as such vast numbers of experiences would be, we should not be aware of them until they were brought by some mysterious agency into the consciousness of the moment. The great mass of the mental experiences of our lives which we have at our command, our extensive educational and other acquisitions from which we consciously borrow from time to time, as well as those which, we have seen, are conserved though they cannot be voluntarily reproduced, all these mental experiences, by the hypothesis, would still have persisting conscious existences in their _original concrete psychological form_.

Such an hypothesis, to my mind, is hardly thinkable, and yet this very hypothesis has been proposed, though in less concrete form perhaps, in the doctrine of the “subliminal mind,” a particular form of the theory of the subconscious mind. This doctrine, which we owe to the genius of the late W. H. H. Meyers, has more recently appeared, without full recognition of its paternity, in the writings of a more modern school of psychology. According to this doctrine our personal consciousness, the ideas which we have at any given moment and of which we are aware, are but a small portion of the sum total of our consciousness. Of this sum-total we are aware, at any given moment, of only a fractional portion. Our personal consciousness is but sort of up-rushes from this great sum of conscious states which have been called the subliminal mind, the subliminal self, the subconscious self. These conscious up-rushes make up the personal “I,” with the sense of awareness for their content.

The facts to be explained do not require such a metaphysical hypothesis. All that is required is that our continuously occurring experiences should be conserved in a _form_, and by an arrangement, which will allow the concrete ideas belonging to them to reappear in consciousness whenever the conserved arrangement is again stimulated. This requirement, the theory of conservation, which is generally accepted by those who approach the problem by psycho-physiological methods, fully satisfies. Before stating this theory in specific form let me mention to you still another variety of the subliminal hypothesis, metaphysical in its nature, which appeals to some minds of a philosophical tendency.

=Conservation considered as an undifferentiated psychical something or “psyche.”=—It is difficult to state this hypothesis clearly and precisely for it is necessarily vague, transcending as it does human experience. It is conceived, as I understand the matter, or at least the hypothesis connotes, that ideas of the moment, after ceasing to be a part of awareness, subside and become merged in some form or other in a larger mind or consciousness of which they were momentary concrete manifestations or phases. This consciousness is conceived as a sort of unity. Ideas out of awareness still persist as consciousness in some form though not necessarily as specific ideas. According to this hypothesis, it is evident that when the ideas of the moment’s awareness subside and become merged into the larger consciousness either one of two things must happen; they must either be conserved as specific ideas, or lose their individuality as states of consciousness, and become fused in this larger consciousness as an undifferentiated psychical something. Some like to call it a “psyche,” apparently finding that by using a Greek term, or a more abstract expression, they avoid the difficulties of clear thinking.

The first alternative is equivalent to the hypothesis of conservation in the form of coconscious specific ideas which we have just discussed. The second alternative still leaves unexplained the mechanism by which differentiation again takes place in this psychical unity, how a conscious unity becomes differentiated again into and makes up the various phases (ideas) of consciousness at each moment; that is, the mechanism of memory.

But, aside from this difficulty, the hypothesis is opposed by evidence which we have already found for the persistence of ideas (after cessation as states of consciousness) in some concrete form capable of very specific activity and of producing very specific effects. We have seen that such ideas may under certain conditions continue to manifest the same specific functionating activity as if continuing their existence in concrete form (e. g., so-called subconscious solution of problems, physiological disturbances, etc.). This phenomenon is scarcely reconcilable with the hypothesis that ideas after passing out of awareness lose their concrete specificity and become merged into an undifferentiated psychical something.[55]

Furthermore, for a concept transcending experience to be acceptable it must be shown that it adequately explains all the known facts, is incompatible with none, and that the facts are not intelligible on any other known principle. These conditions seem to me far from having been fulfilled. Before accepting such a concept it is desirable to see if conservation cannot be brought under some principle within the domain of experience.

=Conservation considered as physical residua.=—Now the theory of memory which offers a satisfactory explanation of the mode in which registration, conservation, and reproduction occur postulates the conserved residua as physical in nature. Whenever we have a mental experience of any kind—a thought, or perception of the environment, or feeling—some change, some “trace,” is left in the neurons of the brain. I need not here discuss the relation between brain activity and mind activity. It is enough to remind you that, whatever view be held, it is universally accepted that every mental process is accompanied by a physical process in the brain; that, parallel with every series of thoughts, perceptions, or feelings, there goes a series of physical changes of some kind in the brain neurons. And, conversely, whenever this same series of physical changes occurs the corresponding series of mental processes, that is, of states of consciousness, arises. In other words, physical brain processes or experiences are correlated with corresponding mind processes or experiences, and vice versa.[56] This is known as the doctrine of psycho-physical parallelism. Upon this doctrine the whole of psycho-physiology and psycho-pathology rests. Mental physiology, cerebral localization, and mental diseases excepting on its assumption are unintelligible—indeed, the brain as the organ of the mind becomes meaningless. We need not here inquire into the nature of the parallelism, whether it is of the nature of dualism, e. g., a parallelism of two different kinds of facts, one psychical and the other physical; or whether it is a monism, i.e., a parallelism of two different aspects of one and the same fact or a parallelism of a single reality (mind) with a mode of apprehending it (matter)—mind and matter in their inner nature being held to be practically one and the same. The theory of memory is unaffected whichever view of the mind-brain relation be held.

Now, according to the psycho-physiological theory of memory, with every passing state of conscious experience, with every idea, thought, or perception, the brain process that goes along with it leaves some trace, some residue of itself, within the neurons and in the functional arrangements between them. It is an accepted principle of physiology that when a number of neurons, involved, let us say, in a coördinated sensori-motor act, are stimulated into functional activity they become so associated and the paths between them become so opened or, as it were, sensitized, that a _disposition_ becomes established for the whole group, or a number of different groups, to function together and reproduce the original reaction when either one or the other is afterward stimulated into activity. This “disposition” is spoken of in physiological language as a lowering of the threshold of excitability—a term which does not explain but only describes the fact. For an explanation we must look to the nature of the physical change that is wrought in the neurons by the initial functioning. This change we may speak of as a _residuum_.

Similarly a system of brain neurons, which in any experience is correlated in activity with conscious experience, becomes, so to speak, sensitized and acquires, in consequence, a “disposition” to function again as a system (lowering of thresholds?) in a like fashion; so that when one element in the system is again stimulated it reproduces the whole original brain process, and with this reproduction (according to the doctrine of psycho-physical parallelism) there is a reproduction of the original conscious experience. In other words, without binding ourselves down to absolute precision of language, it is sufficiently accurate to say that every mental experience leaves behind a residue, or a trace, of the physical brain process in the chain of brain neurons. This residue is the physical _register_ of the mental experience. _This physical register may be conserved or not._ If it is conserved we have the requisite condition for memory; the _form_ in which our mental experiences are conserved. But it is not until these physical registers are stimulated and the original brain experience is reproduced that we have memory. If this occurs the reproduction of the brain experience reproduces the conscious experience, i.e., conscious memory (according to whatever theory of parallelism is maintained). Thus in all ideation, in every process of thought, the record of the conscious stream may be registered and conserved in the correlated neural process. Consequently, the neurons in retaining residua of the original process become, to a greater or less degree, _organized into a functioning system_ corresponding to the system of ideas of the original mental process and capable of reproducing it. When we reproduce the original ideas in the form of memories it is because there is a reproduction of the physiological neural process.

It is important to note that just as, on the psychological side, memory always involves the awakening of a previous conscious experience by an associated idea, one that was an element in the previous system of associated sensations, perceptions, thoughts, etc., making up the experience, so, on the physiological side, we must suppose that it involves stimulation of the whole system of neurons belonging to this experience by the physiological stimulus corresponding to the conscious element or stimulus. For instance, if I see my friend A, the image is not a memory, though it is one I have had many times before and has left residua of itself capable of being reproduced as memory. But if I see his hat, and immediately previously linked pictorial images of him arise in my mind; or, if, when I see him, there arise images of his library in which I have previously seen him, these images are memory. A conscious memory is always the reproduction of an experience by an associated idea or other element of experience (conscious or subconscious). Similarly we must infer that the neurons correlated with any past mental experience are stimulated by associated neuron processes. This is the foundation-stone of mental physiology; for upon the general principle of the correlation of mental processes with neural processes rests the whole of cerebral localization and brain physiology.

Although we assume newly arranged dynamic associations of neurons corresponding to associations of ideas, we do not know how this rearrangement is brought about, though we may conceive of it as following the physiological laws of lowering of thresholds of excitability. Nor do we know whether the modifications left as residua (by which the thresholds are lowered) are physical or chemical in their nature, though there is some reason for believing they may be chemical.

=Chemical and physical theories of residua.=—It is possible that, through chemical changes of some kind left in the system of neurons corresponding to an experience, the neurons may become sensitized so as to react again as a whole to a second stimulus applied to one element. In other words a hyper-susceptibility may become established. There is a physiological phenomenon, known as anaphylaxis, which may possibly prove more than analogous, in that it depends upon the production, through chemical changes, of hyper-susceptibility to a stimulus which before was inert. The phenomenon is one of sensitizing the body to certain previously innocuous substances. If, for instance, a serum from a horse be injected into a guinea pig no observable reaction follows. But, if a second dose be injected, a very pronounced reaction follows and the animal dies with striking manifestations called anaphylactic shock. This consists of spasm of the bronchioles of the lungs induced by contraction of their unstriated muscles and results in an attack of asphyxia.[57]

The mechanism of anaphylaxis is a very complicated one involving the production in the blood of chemical substances called antibodies, and is far from being thoroughly understood. One theory is that sensitization consists in the “fixing” of the cells of the tissues with these antibodies. This may or may not be correct—probably not—and I am far from wishing to imply that sensitization of the neurons, as a consequence of functioning, has anything in common with the mechanism of sensitizing the body in anaphylaxis. I merely wish to point out that sensitizing nervous tissue through chemical changes is a physiological concept quite within the bounds of possibility; and, as all functioning is probably accompanied by metabolic (chemical) changes, such metabolic changes may well persist in neurons after brain reactions produce sensitization.

If this hypothesis of sensitization should be proven it would offer an intelligible mechanism of the phenomenon of memory. If the system of neurons engaged in any conscious experience were sensitized by chemical changes it would acquire a hyper-susceptibility. The system as a whole would consequently be excited into activity by any other functioning system of neurons with which it was in anatomical association and might reproduce the originally correlated conscious experience.

Various theories based on known or theoretical chemical or physical alterations in the neurons have been proposed to account for memory on the physiological side. Robertson[58] has proposed that it is of the nature of autocatalysis. Catalysis is the property possessed by certain bodies called catalyzers of initiating or accelerating chemical reactions which would take place without the catalyzer, but more slowly. “A catalyzer is a stimulus which excites a transformation of energy. The catalyzer plays the same rôle in a chemical transformation as does the minimal exciting force which sets free the accumulation of potential energy previous to its transformation into kinetic energy. A catalyzer is the friction of the match which sets free the chemical energy of the powder magazine.”[59]

Numerous examples of catalytic actions might be given from chemistry. The inversion of sugar by acids, the decomposition of hydrogen peroxide by platinum black, fermentation by means of a soluble ferment or diastase, a phenomenon which may almost be called vital, are all instances. According to Leduc “the action of pepsin, of the pancreatic ferment, of zymase and other similar ferments has a great analogy with the purely physical phenomenon of catalysis.”

In auto-catalysis one of the _products_ of the reaction acts as the catalyzer. Now Robertson concluded, as a result of his experiments carried out on frogs, that the processes which accompany the excitation of the cells of the neurons are of the nature of catalysis; for he found that they have as one effect the production of an acid; and he also found that acids accelerate such processes which he concludes to be probably of the nature of oxidations. “The chemical phenomena which constitute the activity of a neuron cell,” he says, “seem to us then an _auto-catalytic oxidation_, that is to say, an oxidation in which one of the products of the reaction acts as a catalyzer in the reaction.” It occurred to him then that the physiological correlate of memory might be explained on the principle of auto-catalysis. When, to test this hypothesis, he came to compare the results of certain psychological experiments on memory, made by two different experimenters (Ebbinghaus and Smith), with the law characteristic of auto-catalytic chemical reactions, he found that they corresponded in a surprisingly close way with this law. That is to say, assuming the value of the residua of memory (measured by the number of syllables learnt by heart) to be proportional to the mass of the chemical product of auto-catalysis, we should expect that the increase of the number of syllables or other experiences retained by memory following increase of repetitions would obey the law of catalytic reaction as expressed in the mathematical formula established for the reaction. Now, as a fact, he found that the number of syllables that should be so retained in memory, as calculated theoretically by the formula, corresponded in a remarkable way with the actual number determined by experiment. “The agreement was closer,” the author states, “than that which generally obtained in experiments in chemical dynamics carried out _in vitro_.” Robertson sums up his conclusions as follows:

“5th. We have shown that the phenomenon of which the subjective aspect is called ‘memory’ is of a nature indicating that the autocatalyzed chemical reactions form the mechanism conditioning the response of the central nervous system to stimuli.

“6th. In admitting that the extent of the trace of memory may be proportionate to the mass of a product of an autocatalyzed chemical reaction unfolding itself in the central nervous system as the result of the application of a stimulus, we have shown that the relation which one theoretically deduces between the mass of memory material and the number of repetitions corresponds to that which has been found by experience.

“7th. On the basis of the hypothesis above mentioned we have shown that the law of Weber-Fechner admits of a rational physico-chemical interpretation, and that the result thus obtained, provided the hypothesis above mentioned be an exact representation of facts, is that the intensity of the sensation is at each instant proportionate to the mass of the product of the autocatalyzed chemical reaction above mentioned and, consequently, to the extent of the trace of memory.”

While it is easy to understand that auto-catalysis may take part in the chemical process which underlies the performance of simple volition, as inferred by Robertson,[60] and perhaps reproduction in the memory process, it is difficult to understand how such a chemical action can explain conservation. The problem is not that of acceleration of an action, but of something like the storing up of energy.

Rignano[61] has proposed an hypothesis according to which the cells of the nervous system are to be considered as so many accumulators, analogous to electric accumulators or storage batteries. “The similarities and differences which nerve currents present in comparison with electric currents warrant us in assuming in nerve currents some of the properties of electric currents, and in attributing at the same time to the first other properties which the electric do not possess, provided these qualities are not incompatible with the others.”

Now, according to the hypothesis, the specific nervous current set up by any stimulus forms and deposits in the nucleus of the cells (through which the current flows) a _substance_ which adds itself to the others already there without changing them and which is capable, under appropriate conditions, of being discharged and restoring the same _specific_ current by which it was produced. Each cell thus becomes what Rignano calls an _elementary nervous accumulator_. He points out that “both the conception of _accumulators of nervous energy in tension_, and that of _accumulators of a specific nervous energy constituting their specific irritability_,” which the hypothesis includes, are not new but “an ordinary conception very generally employed.”... “The only new thing which the above definition includes is the hypothesis that the substance, which is thus capable of giving as a discharge a given nervous current, _was produced and deposited_ only by a nervous current of the same specificity, but in the inverse direction, and could have been produced and deposited only by such a current.” "In just this capacity of restoring again the same specificity of nervous current as that by which each element had been deposited one would look for the cause of the mnemonic faculty, in the widest sense, which all living matter possesses. And further the very essence of the mnemonic faculty would consist entirely in this restitution.“