Consciousness as a Cellular Function
Psychological consciousness, that intimate feeling of our existence which opposes us to the external world, is irresistibly perceived as marking, at the same time as it establishes it, the superiority of human nature over the material world. "When the Universe would crush him," said Pascal, "man would still be nobler than that which kills him, because he knows that he dies, and the advantage that the Universe has over him, the Universe knows nothing of it." It evidently results from cerebral functioning, but we have no means of analyzing this functioning; we would not know how to recognize consciousness if it manifested itself during a vivisection on the brain of a laboratory animal; it is of its essence to be known only to the individual who is its seat; moreover, by virtue of an obvious and imperative moral rule, it is prior to the operation suppressed by anesthesia. As a physiologist, I would therefore not have much to say, but in a Congress on automatic machines that took place in January 1951, I encountered, in the way I am going to describe, a question of another order that led me to try to formulate a theory on the origin of consciousness. My excellent colleague from the Academy of Sciences, the Duke of Gramont, finding this theory interesting, spoke about it to La Revue, which did me the honor of asking me for an exposition of the ideas I am arriving at in this domain. Let it be understood that the question is posed exclusively on biological grounds; we must seek what one can imagine without resorting to the transcendent notion of a soul existing by itself.
The origin of consciousness? The question, in itself, appears very vague and so to speak elusive; it was, in the Congress, posed in a firmer way, and I dare say more pressing.
"These recent years have seen an abundant flowering of research on machines that control their own functioning and are capable of rectifying it when it deviates 'from their program,' as we say, that is to say from the action plan set by the constructor. Such an error in conduct leads to a reaction, a new process that comes back to the machine, a feed-back (return feed), according to the English expression passed as such into French science.
Feed-back was, without the name, usual in mechanics; notably we have a good example in Watt's governor applied to steam engines for more than a century. A double pendulum suspended on a vertical axis rotates with the machine; centrifugal force pushes the two pendulums away from their axis, the more so as rotation is faster; a suitable lever system causes this displacement to act on the arrival of steam in the motor cylinder: if the machine slows down, more steam arrives and vice-versa.
The number and complexity of mechanisms thus self-governed have become sufficient for one to think of codifying their study in a body of science which it seemed useful to give a name, cybernetics. This specification is generally and rightly recognized as having the American Wiener as its author; but it is not without interest to note that this master of mathematical mechanics had a physiologist collaborator, still young but already well qualified, Rosenblueth. This is because Nature has extensively used the principle of feed-back in the organization of nervous control of our movements; all our voluntary muscles are equipped with sensory nerves that engage the tension of the muscle; and these proprioceptive nerves, as Sherrington who made them known to us in detail called them, result, by reflex, in moderating in the necessary proportion the command of contraction. This mechanism is unconscious; it nonetheless plays an important role in the coordination of voluntary movements; take a pair of antagonistic muscles, let's say the flexor and extensor of the same limb segment. Sherrington has shown that between these two muscles there is reciprocity of innervation; at the precise moment when one begins to contract, the other relaxes in order to facilitate the first action; conversely, at the moment when voluntary contraction ends, the antagonistic muscle contracts in turn to a certain extent to brake the impulse received by the limb which, ballistically, would more or less continue the movement.
The importance of this feed-back appears when it is lacking; for example in locomotor ataxia, a serious walking disorder, where the patient who wants to lift a foot, unable to limit the movement, throws his leg too high and too far; following a certain disease, the small nervous ganglion located near the vertebral column from which sensory fibers in general draw their origin is altered in such a way that proprioceptive fibers are functionally suppressed; the call to the moderating feed-back no longer takes place; and henceforth, with legs whose muscles have kept their power and respond perfectly to contraction orders, whose joints move freely, the patient is unable to walk.
It is therefore not surprising that mechanics and neurologists meet to deliberate on common subjects. The January 1951 Congress was titled: Computing Machines and Human Thought. The comparison with the brain has continually revealed numerous and profound analogies. One of the participants, the Belgian engineer Boulanger, was led to qualify the calculating machine as a "particular case of the reasoning machine," and the French engineer Couffignal, animator of the Congress, announced a book entitled: Thinking Machines, which has indeed just been published.
But the question of consciousness was raised explicitly only in one of the last sessions. It was one of my former students, a student I am proud of, Dr. Paul Chauchard, who posed it in the following way: are these machines that resemble the brain endowed with consciousness? Then, immediately generalizing in a more interesting form, he asked: can one conceive that the organization of individually unconscious pieces, brings about the appearance of consciousness?
Our meeting, as a whole, manifested that the question reflected a general preoccupation. There was a very interesting discussion of which unfortunately only fragmentary notes remain. My memories, in agreement with those of Chauchard, would indicate that the mechanics inclined toward an affirmative answer; biologists, on the contrary, like Chauchard himself, generally thought that consciousness is an appurtenance of life.
I had without reservation, but with a simple word, declared myself in agreement with this second point of view. I would have been hard-pressed at that moment to justify my opinion; it was rather a feeling; I couldn't imagine a collection of metal pieces, a bag of nails, according to the simplistic image that came to my mind, acquiring consciousness after transformation into screws, gears, connecting rods, etc., even by adding electronic tubes or such other physicochemical devices as one would want, and whatever the complexity of their combination. During the year that has just passed, my reflections have expanded and clarified in the same direction. The elements that combine to form all the organs of an animal are living cells. It is important to understand well what this means. Let us examine the question in general terms, without even limiting ourselves to the cells of the nervous system or neurons.
A cell is a small mass of protoplasm, the fundamental substance of any vital organization, more or less similar to egg white; the average weight of an animal cell is well below one-thousandth of a milligram; but small as it is, it has its unity with, in general, well-defined boundaries separating it from neighboring cells. For neurons precisely, a little more than half a century ago, and after a lively debate in which many anatomists took part, headed by Ramon y Cajal, the question was settled in this sense; despite their complicated ramifications that intersect, the nervous elements do not merge, but are contiguous with defined and specialized points of contact, the synapses. Each of these distinct protoplasmic domains is under the dependency of a center that can be seen within the protoplasm, the cell nucleus. The importance of the nucleus had been established ten and fifteen years earlier (Nussbaum, Balbiani), on unicellular organisms; by cutting them in such a way as to obtain a part without a nucleus, one sees this part, in a day or two, disintegrate and disappear, while the part having a nucleus, not only continues to live, to feed, but regenerates what had been removed from it. The same is true for each cell, part of a multicellular organism, notably for neurons (Waller the elder, 1852).
On the other hand, living tissue is irritable, said Glisson in the 17th century. After having been confused with contractility by Haller, irritability was specified and generalized by Virchow in the following definition: active process that appears following a passive alteration.
Waller the younger, at the beginning of this century, found on all kinds of plant or animal tissue, following any trauma, an electrical reaction which he calls blaze-current; with Mrs. Lapicque, by specifying the required conditions for its observation, I recognized that it is a decrease in the positive potential with which the surface of any living cell is charged. For a nerve, this electrical reaction becomes the nervous influx and is communicated to other cells.
In most tissues, the irritation of a cell remains localized; it is revealed under the microscope, better with the ultramicroscope, by a decrease in transparency of its protoplasm; the observation is easy, for example, on an onion skin torn off with care, preserved from desiccation and touched at one of its points with a needle. This colloidal disturbance is the morphological appearance of Waller's blaze-current; it is therefore general. It can be the first stage of a proper function of the tissue, such as muscle contraction. On plant tissue where it does not have such extensive consequences, one can see it either evolve towards total coagulation, that is to say death, or regress, the protoplasm recovering its homogeneity under the influence of the nucleus.
In conclusion, we see that the cell is an organism in itself, with a defined extent, a center of its own and a life distinct from that of neighboring cells. It is an individual, and this individual reacts in a systematic way when it is the object of an intervention from the environment.
Therefore, one is entitled to ask: is it endowed with consciousness?
In what we have just seen, nothing indicates it. But never does the consciousness of another being appear to us directly; even among our fellow humans, we can only affirm it by induction. At the very least, the experimental findings we have noted, tending to make the cell a person, leave room for the hypothesis of cellular consciousness. However, imagination has difficulty in making such a concession to an object so small and which appears inert.
I will therefore evoke certain cellular manifestations which, observed under favorable conditions (magnification and acceleration), give on the contrary a striking impression of psychic life. A white blood cell (leucocyte) is capable of going, even coming out of the vessels through their wall (diapedesis), in search of a microbe or a fragment of altered organ which it must destroy by absorbing and digesting it (phagocytosis). The Laboratory of General Physiology at the Sorbonne has in its collections a beautiful film made by Dr. Comandon, a well-known specialist in microscopic cinematography. Several leucocytes have been caught in action. I have never projected this film, either in my course or in a conference, without the audience manifesting that it was deeply impressed by the sight of these tumultuous monsters colliding, and jostling the red blood cells to make their way in the direction they seem to have chosen.
It would certainly be unjustified to attribute a will to them on the sole faith of this impression; as unjustified as to deny all sensation to the cell which, enclosed in a tissue like a brick in a wall, is incapable of reacting other than by a change in polarization. The theory of tropism, solidly based experimentally, allows us to interpret as purely physico-chemical phenomena the production, on the surface of leucocytes, of excrescences (pseudopods) which seem to make gestures; the same is true for displacement in a determined direction. If there is in the medium diffusion of certain substances, for example soaps, having the property of decreasing the surface tension of the leucocyte, it will tend to spread towards increasing concentrations of these substances; hence emission of pseudopods and overall sliding in this direction. One obtains phenomena of the same kind on a drop of oil containing free fatty acids, rancid oil for example.
It is reasonable to admit that this cellular life, like our own life, involves a material face and a psychological face. Here, as there, according to the expression of a French psychologist prematurely disappeared, Abel Rey, one would mutilate the biological fact if one neglected one of these two essential traits.
Therefore, I admit in each living cell an element of consciousness. This position separates me from the few biologists who have approached this subject, or who, adopting, as Verworn says, the procedure of the ostrich, have explicitly refused to approach it. Le Dantec, a naturalist who, at the beginning of this century, devoted himself successfully to the philosophy of Nature and published in this domain a whole series of esteemed books, wrote in one of the first (New Theory of Life, 1896): "There is no reason to ask if cells think because a being composed of billions of cells thinks."
For Piéron, a contemporary psychologist, who can be considered the head of current French psychology, "the scientific attitude aims to unify as much as possible, and its undeniable ideal is to reduce psychological facts to physiological mechanisms, neglecting the subjective aspect of consciousness."
Henri Roger, a career physiologist who was dean of the Faculty of Medicine of Paris, is even more agnostic; in a volume entitled: Elements of Psychophysiology which he published in 1947, at the end of his life, and which is so to speak his scientific testament, he wrote: "We are incapable of understanding how, during the course of animal evolution, conscious perception has developed; we even find ourselves in the impossibility of formulating a rational hypothesis on its origin and nature."
Sherrington, who, until the end, which occurred a few months ago, of his long life fruitful in experimental research and suggestive theories, was universally honored as a master of nervous Physiology, had himself eluded the question: "The cells of the brain are innumerable," he says; "this consideration reduces to nothing the naive conception of the mental experience of a single cell. To pursue the mind in the unicellular would be equivalent to scrutinizing the stars to perceive a will-o'-the-wisp."
I take the opportunity to protest that I do not represent cellular consciousness in the image of our human consciousness; that the latter can be constituted by the integration of myriads, of millions, of the former does not imply this resemblance; a river is evidently constituted by the integration of innumerable raindrops, and a drop of water is not the image of a river.
After this review of the opinions of biologists, my hypothesis of a cellular psychic life would appear singularly isolated if one did not find in Bergson multiple affirmations in the same sense, for example: "The organized elements that enter into the composition of the individual have themselves a certain individuality and each would claim its vital principle if the individual must have its own:" (Creative Evolution, 1907). The intellectual approach of the spiritualist philosopher is the inverse of ours; instead of seeking whether one can explain consciousness, let's say the soul, starting from an elementary psychism attributed to the cell on physiological considerations, he starts from the existence of the soul to admit elementary psychisms in "the organic elements of the body." Thus our agreement is superficial; we will see it eventually evolve into a radical divergence.
At the same epoch, and moreover while polemicizing against Bergson, the same Le Dantec, who refused to examine whether cells enjoy a psychic element, thought he could affirm that "human consciousness is the integral of elementary consciousnesses." (Science and Conscience, 1908), and he comments, I dare not say explains, his conception like this: "I am led to believe that there exist in the world elements of consciousness of which I only know that, by means of these unknown elements, can be constituted a consciousness similar to mine." He further specifies that these elements of consciousness must relate, not to chemically defined bodies, but to their connections. "Bodies," he says, "have between them chemical attractions, affinities; perhaps one must understand that there are psychic states corresponding to chemical reactions between the elements." This is not a passing fancy, a quip, because Le Dantec confirmed it eleven years later in another volume (The Mechanism of Life.)
Despite the identity of our formulas: integration of elementary consciousnesses, it is very difficult for me to consider this theory as an antecedent to mine, which is based on the affirmation of a consciousness in the cell as an individual. I had to note this anticipated response to Chauchard's question, which, I think, he was unaware of, as I was myself until very recently. It does not seem, moreover, that it ever had a great impact.
In truth, it does not seem to me as easy to represent the fusion of cellular psychic elements as the fusion of water drops. The integration necessary to constitute our own consciousness on this basis poses a problem that must now be examined.
Sherrington insisted with great success on the integrative action of the nervous system. The volume he published under this title in 1906 is in its 7th edition and constitutes without dispute a first-rate reference for all neurophysiologists. But the phenomenon envisaged is rather a coordination, or even a selection between numerous influxes, possibly heterogeneous and even contradictory, arriving simultaneously at the final common path, the motor neuron charged with transmitting an order to a muscle. It is a very important mechanism; but it is not the one we need. Moreover, Sherrington says nothing about the nature of this mechanism; we find no light applicable to our problem there.
Let us look at this first in theory; how can elementary psychic phenomena be added up and organized? These atoms of consciousness that we admit in each cell, would they be capable of flowing out of their maternal cell, to unite with those of neighboring cells? We posit that these cells must each be considered as a person. Now the consciousness of a human person is not directly penetrable for another; policemen who have to interrogate a suspect know something about this; these days the daily newspapers frequently returned to the possible abuses of their efforts to extract the truth from a consciousness that closes in on itself instead of manifesting itself through speech; speech allows each one to transmit to his fellow men, if not the content of his consciousness, at least a more or less approximate expression of this content. Is it necessary to add, although we are hardly likely to forget it, for we all have too frequent experience of it, that this expression can be systematically inaccurate? This is then a lie, good demonstration of the impenetrability of consciousnesses; no one would dare to lie to an interlocutor who could read in the subjective. This impenetrability, moreover, is susceptible to various degrees, either from one person to another, or in the same person according to the disposition of the moment. There are men who are easily brought to confess the truth, and it is well known, for centuries, that after absorption of a suitable dose of alcohol, intimate thoughts tend to pour out; in vino veritas. The use in judicial investigations, debatable and debated use, of certain medications such as pentothal, is only a modern application of this old notion.
We have posited that a cell is an individual; consequently each of the tissues of which our body is composed appears analogous to a crowd, to an assembly; in these it happens that a speaker provokes a collective emotion; his word has realized the integration of individual consciousnesses. Even taking this only as a rhetorical figure, his word has realized the integration of consciousnesses; we can see there an image of the postulated phenomena and seek how a physiological tissue, assembly of cells, could arrive at this result. Cells cannot speak, but they have between them, at least in certain cases, and precisely in the nervous tissues which are particularly interesting for our question, functional interconnections.
Cellular unity does not mean isolation when it comes to neurons. On the contrary, neurons have as their proper function to establish, through their own body, connections between various cells, either close or distant from each other. In this second case, nerves intervene, which, essentially, are filaments of protoplasm emanating from the central mass of a neuron and go, by their extremity, to hook onto any point of another cell. From the first cell to the second, they transmit a variation of electric potential, currently quite well analyzed from the physico-chemical point of view, but which for a long time, under the vague designation of nervous influx, plays the indispensable role attributed by Descartes to animal spirits. This variation is electrically of the minus sign, which in general physiology implies activity; when it arrives at a muscle, it contracts; when it arrives at a neuron, it is excited, which can lead to complicated and diverse reactions; without considering at this moment what these reactions may be, let us simply note that the neuron passes from the state of rest to the state of activity. It is a physico-chemical, physiological activity, and not a psychological activity, but let us admit as a provisional hypothesis that the first will entail the second. I am happy, while waiting for other confirmations, to be able to put this hypothesis under the patronage of Claude Bernard; in an interesting posthumous publication, (Thoughts, 1937,), we find the following formula: "The physical acts on the metaphysical."
A population of nerve cells can thus be the seat of a simultaneous disturbance homologous to the collective emotion of a human assembly. In fact, experimental physiology, without concerning itself with our problem and pursuing without theoretical preoccupation the task of analyzing nervous phenomena, has brought to light, a little more than a quarter of a century ago, a case of this kind which is fundamental.
There exists a serious contagious affection which, from time to time, spreads in Europe and which bears the name of lethargic encephalitis; among its symptoms, it presents an irresistible tendency to sleep; it is evidently a disease of the brain, and when, in autopsies of subjects who died of this affliction, one sought to specify the corresponding lesions, they were regularly found in the base of this organ, more precisely in the mesencephalon.
To understand well what this localization represents, let us first see the anatomical and functional significance of the mesencephalon. In a lower vertebrate, such as a frog, with the vault of the skull removed, one perceives, from front to back, two oblong nervous vesicles; this is the telencephalon (terminal brain), primitively center of olfaction; then two round vesicles, the optic lobes or bigeminal tubercles, centers of vision; with a relatively thick layer of nervous elements located below (floor of the optic lobes), this constitutes the mesencephalon; elongated elements of this floor go, in front to join the telencephalon, and, behind, after having momentarily separated from each other in a diamond shape (rhombencephalon) rejoin to continue with the spinal cord.
The vesicles of the telencephalon, which nevertheless, with the evolution of the zoological series, will become our cerebral hemispheres, that is to say the essential part of our brain, do not at this stage have first-rate importance. When they have been removed, the animal, although having become lazy, straightens up if put on its back, spontaneously resumes its normal sitting pose, jumps with vivacity and precision when pinched; thrown into water, it swims regularly and vigorously. On the contrary, if one cuts the encephalon immediately behind the optic lobes, the animal is nothing more than an inert body, except for reflexes which occur with a mechanical appearance under adequate excitations; it is still a beautiful machine, but it is no longer an individual.
At the level of evolution of Batrachians, the higher coordinations that make the individual therefore depend on the centers located in the mesencephalon. In 1923, Mrs. Lapicque had demonstrated in this region the existence of a functional center which acts on the motor nerves to regulate their excitability. The correct execution of a voluntary movement, commanded by the brain, requires that between its antagonistic innervations, for example flexion and extension, there exists a certain ratio in the sensitivity to the duration of excitations, sensitivity which is measured by chronaxie. This necessary differentiation is created, maintained, suppressed or reversed according to circumstances, notably according to the posture of the limb by an unconscious command which emanates from the mesencephalon. This function, an important part of the coordination of voluntary movements, we found it again, more precise and firmer in Mammals when we together took up this subject a few years later (1928); we called it subordination.
Passing from Frogs to Mammals, one finds the encephalon amplified in an almost monstrous way; taking into account the anatomical similarity known with precision since the end of the last century with the works of Eugene Dubois (from The Hague), its mass is about a hundred times larger; it is the telencephalon especially which has increased, expanding in all directions and folding from front to back; it now puts at the service of the highest innervation, notably of the psyche, all the development it has been able to obtain from its primordially modest endowment dedicated to the sense of olfaction, rudimentary in us; at the back the brain adjoins the cerebellum which has developed on the rhombencephalon. The mesencephalon has remained underneath, relatively very small, invisible without dissection; it happens that it is simply designated as "base of the brain," but it has kept its preeminent functions. It is still it which, by the subordination as we have defined it, prepares the correct obedience to the motor orders of the brain; it has remained for the entire organism a center of coordination of movements. It also presides over the functioning of the brain itself. Here are the rather rapid stages by which one arrived at this second notion.
The origin of it is the observation related above of lesions of the mesencephalon following lethargic encephalitis. The Viennese neurologist von Economo had as early as 1917-1918 suggested from this the existence in this region of a sleep center; he resumed this thesis with more force in 1925; French neurologists convened their colleagues in Paris to discuss the question (International Neurological Meeting, 1927); in the meantime the Swiss psychiatrist Demole had clearly obtained sleep in the cat by injection into the mesencephalon of small quantities of a dilute solution of calcium chloride; the classical pharmacodynamic action of such a solution is a decrease in nervous excitability; by injection of a solution of a potassium salt, which has the inverse property, Demole awakened the animal. Thus one was touching so to speak with the finger a center of wakefulness. After production of other arguments and extensive discussion, the Congress concluded in this sense. Moreover, the following year, the physiologist Hess, from Zurich, who was to receive the Nobel Prize a little later, succeeded by means of electric currents, carried directly to the mesencephalon by fine electrodes placed permanently through the skull and brain, in producing sleep and awakening at will.
Who says wakefulness says consciousness, and sleep, according to its depth, is either the suspension or the obnubilation of consciousness. So we came to speak of a "center of consciousness"; the expression is bad, ambiguous, if not vicious, because consciousness as it is given to us by introspection obviously implies an ample participation of the cerebral cortex. It is the integration of the elements of consciousness presented in the cells of this cortex that is realized by the mesencephalon.
It is remarkable, as P. and J. Chauchard noted as early as 1911, that it is the same nervous organization which, on the one hand regulates the excitability of motor neurons (subordination), on the other hand conditions the conscious activity of the brain. The center in question can be defined more narrowly than by the simple designation, "mesencephalon," because the various physiological experiments all designate, except for slight variants, the same small region. This narrow localization, bringing the center back to a limited group of neurons provides a physiological datum probably applicable to psychological integration. Indeed, whether for subordination, or for maintaining the brain in a vigilant state, the center individualized by Mrs. Lapicque nearly thirty years ago and which deserves to bear her name, acts in a univocal manner; it decreases the chronaxie of the subordinated nervous elements, and this activity is transmitted, not by ordinary influxes, such as those that command motricity, series of more or less brief and rapid electrical variations, but by a more or less stable potential variation; an anelectrotonus in the sense of Pfluger (Monnier and Jasper, 1932).
This characteristic functioning legitimizes the above hypothesis, that the physiological substratum of the integration in question is the action of the mesencephalic center.
Taken from the physico-chemical point of view, this action comes down to an increase in the resting potential of cerebral neurons; that this electrical change translates into a change in cellular psychism, we will admit it by recalling in favor of our opinion the assertion of Claude Bernard, already reported above: "The physical acts on the metaphysical."
Is this center itself the seat of phenomena of consciousness? I do not see how one could find out about this point. What matters is that, in fact, its combination with the brain constitutes a material structure, an architecture of cells whose functioning realizes the mental unity of an individual, his personality seen from the internal side, let us say his spirit by giving to this word the broad meaning that the English language puts in Mind or Spirit. The structure in question includes only a fraction of the cells of the body; they are, it is true, encephalic nerve cells, united to the generality of the others by functional communications; integration is thus realized in several stages, of which the lower ones are purely physiological.
If the theory seemed to leave the domain of physiologists, I would answer that on the contrary it places itself under the patronage of Claude Bernard. Indeed, we read in the Thoughts:
"For a long time physiologists have been preoccupied with the search for the seat of the principle of Life. Life or its principle, is not in any organ, in any apparatus in particular; Life, or its principle, is in the Cell, the cell alone, the amoeboid cell, the white globule, the embryonic cell. This is how Life must be conceived today as being cellular life."
"Formerly Life was considered as an immaterial principle which was lodged in the organism to animate and direct the organs and functions. These are outdated ideas that must be destroyed by establishing new theories based on cellular life."