SOURCE: "Pavlov and Darwin," in Evolution after Darwin, edited by Sol Tax, University of Chicago Press, 1960, pp. 219-38.

[In the following essay, Gantt equates the importance of the scientific discoveries of Pavlov with those of Charles Darwin and surveys Pavlovian and post-Pavlovian research.]

The lives of Pavlov and Darwin overlapped. When Darwin was producing the great work which we now celebrate, Pavlov was a stripling lad of ten years, romping and scuffling with the urchins on the streets of Ryazan in central Russia. They both lived in the great age of the adolescence of science, in the century when science, like a rambunctious youth, felt the cocksureness of the teen-ager.

Darwin's theory of evolution liberated thinking among the masses. He gave to science a freedom from authority; he justified its right to stand in a new field upon facts. Pavlov was perhaps a more militant and conscientious champion of science than Darwin. The liberalization of science for which Darwin was responsible arose more from the impact of the theory of evolution than from any missionary zeal on Darwin's part. But Pavlov had the ardor of the reformer. He felt very much the prevalence of subjective thinking, the vague, confused arguments that permeated the psychology of that period. And it was against this kind of reasoning and false explanations that Pavlov struggled rather than against the existence and the importance of our subjective living.

Although Darwin and Pavlov were unlike in personality and in methods of working, in one major way they resembled each other. Darwin's concepts were compounded from numerous detailed observations—observations made under many conditions, in many organisms, in many environments. Pavlov, too, was a keen observer. Over the portals of the new building for research in Koltushi, erected for him a few years before his death in 1936, he had inscribed the words "Observation and Observation." Not only did Pavlov rely on this attribute in his own experiments, but in epitomizing the characteristics of the scientist, he emphasized the strict collection of facts, the method which Darwin used as the basis for his theory of evolution (Pavlov, 1941, p. 189).

Darwin's theory of evolution, although perhaps less firmly established as a law than are some of the Pavlovian principles, has nevertheless had a more profound effect upon popular thinking than have the discoveries of Pavlov. This is because Darwin's facts seemingly conflicted with the teachings of "orthodox" religion. Darwin has had the effect not so much of confuting the basis for religious beliefs as of defining the proper domains of religion and science.

Pavlov accomplished what was of equal importance for our mental life. He no more settled the age-old riddles of the fundamental nature of mind and of our spiritual life than Darwin solved the fundamentals of religion. But he did show that mental phenomena—the elements of our psychical life—have a physiological component and that in many of their aspects they should be studied by strictly scientific methods, the same methods that had been successfully used in the study of the digestive juices—for which Pavlov received the Nobel Prize in 1903.

This discovery was new in its field, but it was not new in principle for the function of the living organism. The study of the laws of nervous activity by physiological methods involved no principles that had not been employed, e.g., for the study of muscular activity: when we move our arm it can be explained as a voluntary action or as a system of levers and fulcrums according to Archimedes or as a utilization of chemical energy. For the thinking of the general public, this was nothing revolutionary.

But whenever science deals with the most complex functions of the nervous system and its contact with the subjective life and mental life, whether this be in psychology, psychophysiology, or psychiatry, Pavlov's discoveries have a profound influence, an influence which at present is barely realized. The "battle for the mind"¹ initiated by Pavlov is only in its infancy; it is still enshrouded in a good deal of obscurity or even confusion.

Despite the general photographic resemblances between Darwin and Pavlov, their marked differences in personality led to the equally marked differences in their methods. Though both were accurate observers, Darwin's observations were as a naturalist, Pavlov's as an experimenter. Darwin laboriously accumulated facts over a long period and methodically assembled them until they convincingly supported the theory of evolution, which had been known beforehand. Pavlov's observations of laboratory facts were collected with equal care, but he then elaborated them into novel and original theories of brain action, often hypothetical. Also, in theorizing, Pavlov occasionally allowed himself great latitude of generalization, as when he spoke of the "reflex of freedom" and the "reflex of purpose."

PAVLOV ON INHERITANCE OF ACQUIRED CHARACTERISTICS

Both Darwin and Pavlov considered the question of the inheritance of acquired characteristics. Before Darwin, Lamarck had given a dogmatic formulation for the mechanism, and Darwin felt that new traits were passed on to the progeny through the mixing of blood of the parents. Darwin's view, of course, was later superseded by the work of Mendel and subsequently by the principles of the gene theory (Weissmann, Morgan, et al.).

This belief of Darwin's is perhaps one reason why he is so popular currently in Russia. As his views on inheritance are generally known, I shall quote him only briefly:

It seems probable that some actions, which were at first performed consciously, have become through habit and association converted into reflex actions, and are now so firmly fixed and inherited, that they are performed, even when not of the least use (Darwin, 1872, p. 39).

Chauncy Leake quotes a Russian physiologist as follows:

Darwin means to us, perhaps, something a little different from what he means to Western Europeans or Americans. You think mostly of Darwin, I believe, or Darwinism as the ruthless struggle of nature, in which the strong conquer and eliminate the weak; in which nature rends, tooth and claw, and so on. We do not think that is Darwinism. That is Nietzsche and Huxley. But, to us, the important aspects of Darwinism is his principle of the survival of living things on the basis of their adaptations to a changing environment (Leake, 1959, p. 155).

The position of Pavlov in supporting Lamarckianism is surrounded by confusion, chiefly from two sources. First, although Pavlov often asserted in the 1920's that some of the educational efforts of the Bolsheviki were misdirected—because they considered as conditional reflexes what were really unconditional reflexes and therefore unmodifiable through education—he has been used as a champion of environment versus heredity by the dominating Lysenko school in the U.S.S.R. in its emphasis on modification by environment and in its struggle against the geneticists.

Second, this seeming contradiction in Pavlov's beliefs stems from a paper he read in 1923 concluding that conditional reflexes established experimentally in mice could be inherited—a position that Kleitman and Razran emphasize he did not refute (Razran, 1958). In the speech, delivered to the Eleventh International Physiological Congress meeting in Edinburgh, Pavlov said, apropos of inheritance:

The latest experiments (which are not yet finished) show that the conditioned reflexes, i.e., the highest nervous activity, are inherited. At present some experiments on white mice have been completed. Conditioned reflexes to electric bells are formed, so that the animals are trained to run to their feeding place on the ringing of the bell. The following results have been obtained:

The first generation of white mice required 300 lessons. Three hundred times was it necessary to combine the feeding of the mice with the ringing of the bell in order to accustom them to run to the feeding place on hearing the bell ring. The second generation required, for the same result, only 100 lessons. The third generation learned after 30 lessons, the fourth generation required only 10. The last generation which I saw before leaving Petrograd learned after 5 repetitions. The sixth generation will be tested after my return. 1 think it very probable that after some time a new generation of mice will run to the feeding place on hearing the bell with no previous training.

It is well known that a chicken when it just comes from the egg immediately begins to pick up any black spot on the floor trying to find some grain, thus showing that it was an inborn reflex from the eye to the food. Why should we not build up the same reaction, not from the eye but from the ear as indicated in the case of the white mice? (quoted in Razran, 1958).

Razran points out in his paper, "Pavlov and Lamarck," that the theme of this address was not primarily inheritance of acquired characteristics, that this was "really only a small, but striking, aside." Previously, as Razran mentions, Pavlov had inclined to the view that it was possible for some habits to become fixed by heredity, viz., the unconditioned reflexes. For example, Pavlov said in 1913: 'One may suppose that some of the conditional temporary connections may be later transformed into unconditional reflexes by heredity" (1928, p. 236). Again, in 1914, he said, "It is highly probable (and there are to this effect some factual indications) that, when the same conditions of life are maintained in series of successive generations, newly formed conditional reflexes uninterruptedly become constant unconditioned reflexes" (1928, p. 242).

Razran says, "No mention whatsoever was made of the problem in any of Pavlov's subsequent writings before 1923."

Much attention has been devoted to the postwar conflict in the U.S.S.R. between Lysenko and Michurin, on the one hand—the champions of environmental influence—and the geneticists represented by Vavilov and I believe earlier by the views of Kozlov. There has been so much written in this country concerning Lysenko and his claims that it is unnecessary to give details. Although the question of environment and heredity still has its different advocates, the opinions of competent authorities such as H. J. Muller, who spent eighteen months in Russia and knew both sides of the Vavilov-Lysenko controversy, indicate that Lysenko's claims are political rather than scientific (Zirkle, 1950).

The question of Lysenko's false claims is not so much of interest to us as is his effect in Russia on the views attributed to Pavlov there. Pavlov has been set up twenty years after his death as in violent opposition to Morgan and the Western geneticists, whereas Morgan's statement in regard to the 1923 address is by no means the virulent, anti-Pavlovian attack which the Russians have attributed to him. Morgan said, "There was some consternation in 1923 when the great Russian physiologist, Pawlow, reported the results of experiments that go far beyond what most Lamarckians have dared hope. Pawlow's conclusions—and as yet we have only his conclusions—are very surprising" (1925, p. 157).

I was in Pavlov's laboratory at the time that the experiments in question were being conducted by Studentsov; the purpose was to determine whether successive generations of mice would form conditional reflexes more quickly then their forebears. There was an ingenious apparatus, designed by Professor Hanike, by means of which laboratory mice were given all their feedings preceded by a conditional stimulus. At this signal the mice went from one cage into another, where they received food, and the number of times before they learned to go when the bell rang was recorded. Studentsov reported the facts of the lesser number of trials required for successive generations of mice to learn, as mentioned in Pavlov's Edinburgh address.

Studentsov died before the end of the experiments, I believe after they had been carried through 11 generations. When, with Pavlov's emphasis on thorough control of experiments and his habit of giving the same theme to at least two, sometimes three, collaborators working in different institutions, this problem was assigned to another investigator, the results did not show that successive generations formed the conditional reflex of going into the food cage at the signal any more quickly than did their forebears. The repetition of these experiments was done, as I recall, about 1924-26.

Since the later experiments turned out negatively, i.e., did not support inheritance of conditional reflexes, and since Pavlov had never read a paper the main theme of which was the inheritance of acquired characteristics, no significance is to be attached to the fact that he did not write a special article retracting these views. In fact, in the bibliography of his Lectures on Conditioned Reflexes, there is no record of any article by Studentsov or on the subject of inheritance.

I have described Pavlov's revised experiments as follows:

The apparatus for forming conditioned reflexes in mice is very ingenious; it was perfected by Professor Hanike in 1925. When a given bell sounds, the mice run to a certain place to get food, and in going there they have to cross a platform attached to springs. When they step on this platform the act is registered on a revolving drum. A revision of the former work on inheritance of conditioned reflexes is being carried out with an entirely new apparatus. The mice now receive all their food (twenty times during each night) preceded by the bell. It is all done mechanically, so that the presence of the operator is not required. A clock arrangement makes twenty electrical contacts during the night (the natural time for the feeding of mice), rings the bell, and a few moments later opens a valve which allows grain to drop into a certain compartment of each cage. When the bell rings there is a general migration of the mice into the "dining room." The mice never get food without the bell. Males and females are kept in separate cages, so that the number of oncoming generations can be carefully regulated. When an experiment is made the mice are removed to a special cage where the results can be registered automatically (Gantt, 1928).

In a discussion which I had in 1926 with Pavlov about this work, he told me that his conclusions about the inheritance of acquired characteristics was one of the biggest errors of his scientific career. He attributed the mistake to the fact that he accepted—contrary to his usual custom—the results of Studentsov without personally supervising the experiments. He told me then that he had given the problem to another collaborator, whose results did not confirm those of Studentsov.

Neither in this case nor in any other is there evidence that Pavlov tended to cling to his theories or his concepts when further facts did not support them. Like other scientists, he made errors. One of these was his statement that the regulation of the pancreatic secretion was effected solely through the nerves. The discovery by Bayliss and Starling of the hormone secretion overthrew Pavlov's theory of nerve control as the sole regulator. To give up this conviction was difficult, but Pavlov stated to his collaborators after he had confirmed the experiments of Bayliss and Starling: "Of course they are right. We cannot claim to a monopoly on all scientific truth."

PAVLOV AND TYPES

Darwin's teachings emphasize the almost imperceptible gradations occurring in nature between different organisms in the process of evolution. Ernst Mayr (1959) emphasizes how the Darwinian cannot be a typologist:

Darwin introduced into the scientific literature a new way of thinking, "population thinking." What is this population thinking and how does it differ from typological thinking, the then prevailing mode of thinking? Typological thinking no doubt had its roots in the earliest efforts of primitive man to classify the bewildering diversity of nature into categories. The eidos of Plato is the formal philosophical condification of this form of thinking. According to it there are a limited number of fixed, unchangeable "ideas" underlying the observed variability, with the eidos (idea) being the only thing that is fixed and real while the observed variability has no more reality than the shadows of an object on a cave wall, as it is stated in Plato's allegory. The discontinuities between these natural "ideas" (types), it was believed, account for the frequency of gaps in nature. Most of the great philosophers of the 17th, 18th and 19th centuries were influenced by the idealistic philosophy of Plato, and the thinking of this school dominated the thinking of the period. Since there is no gradation between types, gradual evolution is basically a logical impossibility for the typologist.

The ultimate conclusions of the population thinker and of the typologist are precisely the opposite. For the typologist, the type (eidos) is real and the variation an illusion, while for the populationist the type (average) is an abstraction and only the variation is real. No two ways of looking at nature could be more different.

Pavlov said that the great difference between the human and the subhuman animals was in the language function, which he called the "second signaling system." He recognized that language represents a new function, present only in the human, upon which is based the quality responsible for the superior advances of Homo sapiens, viz., the capacity for symbolization and abstraction. Pavlov considered words not only as secondary signals—the signals of signals—but as a distinct and new function of the brain.

Here is introduced a new principle of higher activity (abstraction—and at the same time the generalisation of the multitude of signals of the former system, in its turn again with the analysis and synthesis of these new generalised signals), the principle of the conditioning limitless orientation in the surrounding world and of creating the highest adaptation of the human—science both in the form of a humanitarian empiricism as well as in its specialised form (1941, p. 114).

Pavlov divided the human being (perhaps without sufficient justification) into two main types according to the extent of the development of the second signaling system: In the first group were those who used mainly the first signaling system (e.g., artists), and in the second group were those with a more highly developed second signaling system—the scientist, mathematicians, etc., who depend chiefly upon abstractions. That Pavlov considered this function a definite human one is attested to by his statement (1941, p. 162):

Until the time when Homo sapiens appeared animals were connected with environment so that the direct impressions fell upon the different receptors and were conducted to the corresponding cells of the central nervous system. These impressions were the several signals of the external object. However there arises in the developing human an extraordinary perfection, the signals of the second order, the signals of the primary signals in the form of words—the spoken, the heard, the seen word. Finally it came about that through these new signals everything was designated that the human being perceived both from the environment and from his inner world, and these signals commenced to serve him not only in communicating with other men, but also when he was alone.

The theory of natural selection rests upon the breaking-down of types. Pavlov, on the other hand, found definite variations among his dogs which led him to put them into four categories based upon the Hippocratic division into four temperaments—the extremes of choleric and melancholic, and the middle types of sanguine and phlegmatic (1928, p. 370).

Although the division into four rigid types on the basis of the predominance of excitatory and inhibitory conditional reflexes, as well as on the general behavior, may not be entirely satisfactory, there does seem to be some division possible, derived from the circumscribed conditional reflex studies in the dogs. In my own studies, although I have not been able to substantiate the strict conformity to the four Hippocratic temperaments, I do find it profitable to divide the dogs into groups according to their susceptibility to stress (Gantt, 1943).

Recent work from Russia on the typology of dogs, as well as of the human, is even more promising. Thus the work of Krasusky on the reaction of dogs to certain drugs (e.g., caffeine) is claimed to give a more rational basis for a classification of types. Krasusky makes the important revision in describing the behavior that external behavior is not to be taken as an adequate criterion, since this depends to a great extent upon what the individual is accustomed to, such as the presence of the human being, its early training, and environment. This work depends upon concepts that seem to be opposed to those of Lysenko. Though heredity is emphasized in Krasusky's research, there is no definite mention made of its relation to Lysenkoism.

A biochemical basis for a study of types in the human being has been laid by the Protopopov School of Psychiatry in Kiev. Their results support the view that manic psychotic attacks can be predicted by biochemical and metabolic studies some months before they occur and can be prevented by appropriate therapy.

VALIDITY OF DARWIN'S OBSERVATIONS IN THE LIGHT OF MODERN RESEARCH

In his book The Expression of the Emotions in Man and Animals (1872) Darwin made profound deductions from careful observations, but his formulations have been neglected in the century since publication. I must admit that I was also unaware of Darwin's concepts on these subjects until this year. However, his formulations, made without benefit of laboratory or equipment, are so close in many cases to what I have found over the past thirty years by the conditional reflex methods that I must insert a digest of his observations, gathered from various statements throughout his book and placed here under the headings by which we now express the topics.

SCHIZOKINESIS

AS I have defined this principle, it involves (1) specifically, a lack of parallel between the general autonomic (respiratory, cardiac) patterns and the more voluntary motor ones and (2) the extension of this principle to a persistance of useless reactions to the environment, representing maladaptations. There are at least twelve separate references in Darwin's book to differences between cardiac and muscular responses, similar to those I have seen in the laboratory and which I call "schizokinesis." Thus on page 28 Darwin says, "Some actions ordinarily associated through habit with certain states of the mind may be partially repres-sed through the will, and in such cases the muscles which are least under the separate control of the will, [the cardio-respiratory] are the most liable to act, causing movements which we recognize as expressive."

He goes further and states: "In all cases there seems to exist a profound antagonism between the same movements, as directed by the will and by a reflex stimulant, in the force with which they are performed and in the facility with which they are excited." Darwin also invokes the support of Claude Bernard: "L'influence du cerveau tend donc à entraver les movements réflexes, a limiter leur force et leur étendue."

In regard to the principle of schizokinesis (maladaptation) in disease Darwin quotes Maudsley as saying that "reflex movements which commonly effect a useful end may, under the changed circumstances of disease, do great mischief, becoming even the occasion of violent suffering and of a most painful death." According to Darwin, many of these responses that he states become purposeless or even harmful do so through a relationship between another emotional state and the original one, so that the secondary emotional state may produce an entirely inappropriate response. Many examples are given, such as cats shaking their feet at the mere sound of flowing water, as if they were actually standing in it, and the pounding of kittens with their extended claws against numerous objects, a movement appropriate only for the mother's mammae.

In regard to the self-destructiveness of the cardiac reaction, he says, "The heart beats quickly, wildly, and violently; but whether it pumps the blood more efficiently through the body may be doubted, for the surface seems bloodless and the strength of the muscles soon fails." Darwin repeatedly emphasizes the maladaptability of certain habits (conditional reflexes): "My object is to show that certain movements were originally performed for a definite end, and that, under nearly the same circumstances, they are still pertinaciously performed through habit when not of the least use" (italics mine).

CARDIAC CONDITIONAL REFLEX

Although the existence of a cardiac component of the conditional reflex has not yet been recognized in physiology in this centenary year, Darwin repeatedly cites well-known instances of what could be called a cardiac component of the conditional reflex: "When a man or horse starts, his heart beats wildly against his ribs, and here it may be truly said we have an organ which has never been under the control of the will, partaking in the general reflex movements of the body." The relationship is clearly expressed by him on page 73: "When the heart is affected it reacts on the brain; and the state of the brain again reacts through the pneumogastric nerve on the heart; so that under any excitement there will be much mutual action and reaction between these, the two most important organs of the body. . . . We must not overlook the indirect effects of habit on the heart."

Again he points out that this is so even though the heart is not "under the control of the will." A clear statement of cardiac conditioning follows indicating that muscular exertion is not the cause of the increase in cardiac activity: "On the principle of association, of which so many instances have been given, we may feel nearly sure that any sensation or emotion, as great as pain or rage, which has habitually led to much muscular action, will immediately influence the flow of nerve-force to the heart, although there may not be at the time any muscular exertion."

He states further that when the cerebrospinal system is highly excited "violent movements follow," and he points out that "voluntary muscular exertion relieves pain. . . . The anticipation of a pleasure leads to purposeless and extravagant movement. . . . Persons suffering from grief seek relief from violent frantic movements" (p. 176). In infants, too, he observes that "screaming brings relief."

All these observations by Darwin are strikingly parallel to what we have observed in the laboratory—that a quiescent state follows intense activity (Cruet and Gantt, The Bulletin of the Johns Hopkins Hospital, December, 1959).

EFFECT OF "PERSON"

We have devoted considerable attention at our Laboratory to the marked influence on dogs of the presence of other dogs and of human beings. We have seen an especially strong effect during tactile stimulation, such as rubbing behind the ears; in some animals the heart rate is reduced from 160 to 40 or less.

Darwin notes the wide prevalence of the effect of tactile stimulation in nature, plus a "strong desire to touch the beloved person. . . . Dogs and cats manifestly take pleasure in rubbing against their master and in being rubbed. . . . Monkeys delight in fondling and in being fondled" (1872, p. 233). He mentions kissing, rubbing noses, patting of the arms, etc. as human expressions, regarding kissing as innate "insofar as it depends on the pleasure derived from contact with the beloved person" (p. 352). He also describes a patient with heart disease and an extremely irregular pulse which "invariably became regular as soon as my Father entered the room" (p. 339).

While not agreed as to whether this desire for social contact is innate and constitutes a homeostatic drive, psychologists are well aware of its importance to mental health; much clinical data is accumulating on the effects of personal isolation and the implications of family environment for subsequent intellectual and personality growth.

EARLY LEARNING

In recent years the sterile environment-heredity issue has been succeeded by studies of a number of more specific factors that determine learning. There is an awareness of "critical periods," at which the individual reaches a state of maturation that facilitates learning of a particular skill or where he "suddenly" begins to respond to a certain set of environmental stimuli.

The phenomenon of "imprinting," introduced by Heinroth in 1911 and since studied in many species using various behavioral items, occurs at an exceptionally early age and involves sudden learning of a very tenacious sort. Perhaps the best-known example is that of Konrad Lorenz' greylag geese who were hatched in isolation by him and thereafter, as their behavior clearly indicated, regarded him as their mother.

If the young individual at a readiness point is not given opportunity in the form of the necessary equipment or a reasonable substitute or if he is denied the freedom to act, the normal behavior involved may fail to appear. Young mammals at Liddell's "Animal Behavior Farm" at Cornell, separated from their mothers soon after birth, failed to develop skill in sucking. Such was probably the case leading to observations by Hippocrates and by Harvey and later quoted by Darwin in The Expressions of the Emotions, namely, that "a young animal [removed from its mother] forgets in the course of a few days the art of sucking, and cannot without some difficulty again acquire it." An interesting corollary is the oft-observed refusal by the mother to accept the return of the offspring which has been snatched away.

There is certainly an element of timing here, too. Soon after birth, or later at "weaning-time," the young animal readily adapts to substitutes for mammae. However, being separated at a point in-between from that to which he has become accustomed, may result in abnormal and even fatal behavior.

Another learned item, eating habits, play a prominent and often pernicious role. Darwin (1872) refers to various caterpillars that, having regularly fed on the leaves of a particular tree, refused to eat the leaves of another kind of tree, although it could have supplied all their nutritional needs. We have observed similar food habits in dogs, and Stefansson has told me that arctic dogs refuse meat, which is not customarily part of their diet.

POST-PAVLOVIAN RESEARCH

The main concepts of Pavlov have stood firm against assaults, as have the principles he derived. Many of his statements which he regarded as working theories are still in the realm of theory: difficult differentiation as the source of experimental neuroses; the nature, perhaps even the existence, of the processes of induction; concentration and irradiation, as he conjectured them; the explanation of sleep as the spreading of internal inhibition. On the other hand, many of his theories have later been supported by facts; thus, long before the discovery of chemical transmitters such as acetylcholine and sympathin, Pavlov postulated that excitation and inhibition in the brain depend upon definite chemical substances.

EVOLUTION OF CONDITIONAL REFLEX FUNCTION

Using two criteria for the extension of the conditional reflex, (1) formation of the positive reflex and (2) its differentiation, Pickenhain (1959) concludes that in Hydra, Infusoria, and other organisms up to the echinoderms, there is a summation of excitation rather than new formation of the conditional reflex.

A central nervous system is necessary for the conditional reflex. Boycott and Young formed food and defense, excitatory and inhibitory, conditional reflexes in goldfish. Through extirpation of the phylogenetically most recent formations, viz., the cerebral ganglia, the conditional reflex formation was impaired or destroyed. Voronin formed conditional reflexes to light and to defense in crabs; these could be extinguished but were spontaneously restored the next day. In many insects conditional reflexes have been elaborated. Nikitina produced secretory fibers based on temperature in silk worms after 10-15 reinforcements, using change in light as stimulus. In bees Von Frisch has formed many diverse conditional reflexes reinforced by sugar syrup. Voskresenskaya determined that the head ganglion in the bee was required for the conditional reflex. Fankhauser and Vernon showed in salamandors that the number of ganglion cells is related to the conditional reflex formation. Simple formation of conditional reflexes, as well as differentiation, occurs after virtually the same number of reinforcements throughout the animal kingdom. Thus Angyan of Budapest states that he was able to form conditional reflexes in worms after 7 reinforcements. But how the experiments are performed is also important, as shown by the work of Voronin; he obtained formation in crabs after 25-50 reinforcements; in fish, after 30-45; in birds, after 40-120; in rabbits, after 47-107; in dogs, after 3-36; in chimpanzees, after 4-6 reinforcements.

For optimal formation of the conditional reflex in the various genera, it is necessary to observe the natural living conditions and not to base conclusions too strictly on the artificial laboratory environment, e.g., fish are grossly disturbed by an environment in which birds, rabbits, and higher animals are undisturbed. Also fish can form conditional reflexes to such complex stimuli as light plus tone better than to these separately. Nor can fish form trace reflexes where the interval is longer than 5-10 seconds. Trace reflexes are difficult in fowls, rabbits, and dogs, and unstable, while in apes inhibition is elaborated after 3 reinforcements and can be retained, as shown by Voronin, for 8 years.

The development of a centralized nervous system is expressed (1) in the ganglionic chain of the insects and (2) in the central nervous system of the chordates, with its opportunity for plasticity. There is added another mechanism, that of language, Pavlov's second signaling system, in the human being. A primitive form of abstraction is present in subhuman species, some of which can differentiate 7 different kinds of optical stimuli, e.g., in some birds 2 and in others 7. These abstractions seem to be limited in various analyzers to 7 possibilities, and even in the human being with tachistoscopic stimuli it is said that there can be only 7 good differentiations (Pickenhain, 1959).

It is interesting to emphasize that the simple formation of the conditional reflex occurs with nearly the same speed in all animals, viz., after a few combinations of the environmental situation and the unconditional stimulus. But the conditional reflex, though formed, may not be overtly expressed, as I have demonstrated with the cardiac conditional reflex.

The cardiac conditional reflex may be formed in the dog after 1 reinforcement, while the motor conditional is not seen until after 30 or 40 reinforcements, a phenomenon which I call schizokinesis.

The difference among the species of animals is not in the speed of the formation of the simple conditional reflex, but in the complexity, elaborations, and extension of the symbolizations that are possible. In the area where there can be formation, however, there is comparable plasticity in adaptation, which means that the lower animals can adapt to those situations within their limitations with the same readiness as can those animals higher on the zoological ladder.

The comparable speed of formation of the conditional reflex throughout the animal scale may rest upon a basic property of nervous tissue. This finds a parallel in the statement of von Murait that everywhere in nature the passage of the nerve impulse is mediated through acetylcholine or nor-adrenalin, and everywhere the conversion of energy into movement occurs by one mechanism, viz., the chemical change involving adenosine triphosphate (ATP).

EXTENSION OF PAVLOVIAN CONCEPTS

Many other responses and reactions in the organism have been brought within the CR methodology since Pavlov. Bykov (1957) in Russia has done more than anyone else in this field. He has shown that renal secretion of urine, metabolic exchanges, thermal regulation of the body, hormonal secretions, ovulation, electrophysical components, and many others can be readily elaborated as CR's. In the Pavlovian Laboratory of the Johns Hopkins Medical School, we have also extended this field to include vestibular reactions of equilibration (Gantt, Löwenbach, and Brown, 1953), respiratory and cardiovascular responses, including heart rate and blood pressure (Dykman and Gantt, 1958; Gantt and Dykman, 1957), as well as responses to stimuli placed within the central nervous system (interoceptors) (Bykov, 1957). In the human being we have added to these the psychogalvanic response (Reese, Doss, and Gantt, 1953).

The cardiovascular conditional reflex.—Our chief interest since 1939 has been a study of the cardiac responses.

I began this with Dr. W. C. Hoffmann, who came from Norway as a Rockefeller Fellow to work in my laboratory in September, 1939. The cardiovascular responses have both advantages and disadvantages for this type of work. The disadvantage lies in the widespread connections of this system with nearly all events occurring within and outside the organism and the consequent difficulty of controls and isolation of the individual. The advantage of including the cardiovascular system is that, on the theoretical side, it reveals mechanisms, to be pointed out subsequently, which we could never discover from the conventional secretory or motor components. Moreover, the cardiac response, unlike the motor and secretory, can give a measure below zero, as it were, viz., by a decrease in heart rate (HR) or blood pressure below the control, whereas with movement or with secretion, we cannot get such a negative measure, since the absence of secretion or movement is as far as we can go at present without complicated procedures, e.g., muscle potentials.

The first question that concerned us was whether there really existed a cardiovascular conditional reflex—which, for the sake of brevity, I will call the "HR-CR." The majority of physiologists and cardiologists whose opinions we sought were inclined to the view that the cardiovascular system would not participate to a measurable extent in the CR. There is, of course, another aspect of the question, and that is whether there is a cardiac CR to an adequate stimulus to the heart, as well as whether the cardiac system participates as a component in responses that are not primarily specific to the heart, viz., food and slight faradic stimulation. This has not been investigated so thoroughly, although there is sufficient evidence of a specific cardiovascular response to adequate stimuli.

To epitomize two decades of work from my laboratory on the cardiac reactions: the cardiac component of the CR's are, in general, parallel to the secretory and motor; there is a quantitative relationship with the intensity of the excitatory CR, a marked difference between the cardiac component of the excitatory and inhibitory CR's, a precise cardiac time reflex, etc. The inhibitory CR is characterized by a slight rise in HR, with a marked subsequent decrease below normal. Here we have in the cardiac response a measure of inhibition which gives an explanation to the quiescent phase and sleep, which Pavlov found resulting from inhibitions.

More important, however, than the resemblances between the specific CR movements and secretions and the cardiac rate (HR) component of the CR are the differences. First, the cardiac response is often the more sensitive of the measures we have employed. Second, contrary to our expectation, the HR-CR appears more quickly than either the motor or the secretory component. Thus it is often necessary to give 50-100 reinforcements before we see the elaboration of the CR to the motor or to secretory stimuli. But with the cardiac measure, we often see that a CR is formed after one reinforcement with the unconditional stimulus (food or pain) (Pinto, Newton, and Gantt, 1957). This quick formation of the CR explains much that was not evident previously; thus from laboratory studies it appeared that many repetitions were necessary to produce the CR, while the experiences of life showed that a CR was frequently formed after one coincidence of a physiological stimulus and its symbol, e.g., a single coincidence of a strong emotional experience often resulted in, at a later time in life, the same feelings being reproduced, although the original and real physiological unconditional stimulus was subsequently, as at first, lacking (Gantt, 1957).

Schizokinesis.—Now another unexpected event appeared to us. If the heart was sensitive enough to respond so quickly, would these earliest-formed CR's also disappear more quickly? Ask yourself the same question, and see whether you do not predict, as we did, that the cardiac CR's would be unstable and disappear more quickly than other components. In many, though not all, individuals, however, the HR-CR's are extremely stable; once formed, they outlast the more specific components, such as secretion and movement. In many dogs, even after repeated attempts to extinguish, the cardiac CR persisted as strong as ever and for as long as one to four years without practice, while the secretory and motor components remained extinguished!

This marked difference—the early formation and the extreme durability, in contrast to the greater plasticity of the specific secretory or motor responses—is what we have called schizokinesis (Gantt, 1953). In this term I intend to include not only in a narrow sense a difference between the general emotional components of the acquired responses and the specific ones, but in a broader way the lack of perfect adaptation that exists in our biological systems. The heart is doing one thing, out of adaptation to present reality; superficially, the individual may be in repose and undisturbed, but beneath, in the autonomic components of the response, there may be violent turbulence. Here may lie the explanation for the persistence of psychogenic hypertension to past experiences long forgotten (Gantt, 1957).

The tremendous advantage of the conditional reflex is the adaptability of the individual dependent upon experience. This adaptability consists in a readiness to act to the signals of an event and a certain plasticity added to the more stereotyped inborn reactions inherent in structure. But the increasing complexity of the conditional reflex function, seen especially in the human being, carries with it a great liability. First, on account of the complexity, there is a greater possibility for malfunction, just as there is a greater probability of a complex machine going wrong. Second, as we amass conditional reflexes, in order to preserve adaptability, there are of necessity more and more inhibitions with their consequent stresses. Third, as pointed out in connection with schizokinesis, these inhibitions are frequently only partial and imperfect adaptations. Thus, through an accumulation of only partially adaptive conditional reflexes, the individual becomes increasingly a museum of antiquities.

Autokinesis.—In several decades of studying neurotic as well as normal dogs, I have been struck by the changes occurring over a long period, based on past experiences but developing in the absence of the repetition of the original experience. Thus in "Nick" appeared a whole train of neurotic symptoms related to the original stress, but developing and becoming worse during 3 years when the animal was removed from this environment. Even more severe symptoms developed in "V3." These are examples of negative autokinesis, but there is also evidence of a positive autokinesis, e.g., when a single therapeutic conference or some single experience in the life of an individual has a profound and lasting effect for good. In the normal animal, autokinesis can be seen in the elaboration of new relationships among the original excitatory foci, modifying or completely changing the relationship between the conditional reflexes.

This is a circumscribed view of autokinesis, but one may conclude that there is a normally occurring basic principle of inner development—that this is a basic physiological law. Besides the examples from my laboratory, which provide striking contrasts because we have quantitative measurements for comparison and precise stimuli, there are a host of other examples from the laboratories of other workers, as well as from ordinary life. Embryology itself is an example of development determined from within, changes depending upon the internal structure more than on the external environment.

Although the peripheral impulses go into the cortex in specific patterns according to the receptor with definite mosaic arrangements, as shown by Vernon Mountcastle (personal communication), beyond that point is the possibility for integration, combination, and change. The neurological basis for such changes is described by Eccles (1958) in regard to synapses: "The initial activation of the synapses brings about a lasting improvement in the efficacy of these functions. . . . One explanation is that the synaptic knobs grow in size, another that the synaptic transmitter substance is increased." When he says that "usage enhances synaptic efficacy for days or months," here is evidence of central, internal change. Pavlov's action of induction over periods far beyond the action of the stimulus, his interaction of cortex and sub-cortex, are reinforced by the more recent "reverberating circuits" of the electrophysiologists. The effects of cerebral trauma on memory of events within 20 minutes of the trauma indicate that demonstrable changes are proceeding in the brain for at least this length of time after the stimulation has ceased.

These facts constitute the sketchy outlines of a shifting inner structure, with remodeling and rebuilding going on within. This function and capacity to change from within is what I mean by autokinesis.

This is something new for the organism. It apparently involves a changed relationship between centers in the central nervous system, and it occurs as the result primarily of new relationships within the organism. Since the organism is a little universe of its own, why should there not be possible changes occurring between the units of this organism on the basis of internal stimulation? Besides these facts, is there anything more impossible for reciprocal relations to be changed internally, among the inner centers of excitation, than for the organism to be capable of changing in respect to the external environment?

There is too much evidence to refute this idea. Its recognition will open up an entirely new field for exploration, a field which requires special emphasis for its future scientific development. This is an endeavor in which psychiatrists as well as physiologists should join.

The principle of homeostasis, so well developed by the genius of Claude Bernard and amplified by Cannon, now needs to be joined by the principle of schizokinesis and autokinesis, equally cogent for the understanding of normal behavior and psychopathology.

CONCLUSIONS

The conditional reflex function—at the apex of the evolutionary process—is itself not only an asset but a liability. Even more so is the supreme development of this function as represented by the second signaling system of the human. Not only do our great successes in science, mathematics, and literature rest on this quality but also our tragic failures—prejudices—and often our cataclysms of destruction—individual, national, international. Not only can the individual be categorized, branded, and persecuted through the function of such words as "capitalist," "Nazi," "Communist," and racial designations, but wars, with their annihilation of millions of lives, can be waged on the same basis.

Darwin's observations reveal the plasticity inherent in living organisms, the ability to cope with the environment, and the marvelous function for adaptations throughout the ages, while Pavlov's work on the conditional reflexes emphasizes the ability of the individual to adapt during its life.

To criticize Darwin and Pavlov because they did not discover what could not be discovered until their original contributions had been made and understood is not justifiable. Such criticism cannot be made by those who understand the history of science. Because Darwin did not enunciate the principles of Mendelism and of the later geneticists and because Pavlov did not demonstrate the role of acetylcholine or reveal the exact mechanism of inhibition or arrive at a final classification of types—these do not constitute scientific errors. Science has to take one definite step before it can attempt the next, and the next step will often give a point of view which will reveal the previous one in a perspective which was not possible before. Voltaire, in discussing Descartes, pointed out that he should no more be expected to make all the necessary elaborations of his theories which were made later than could Columbus be expected to describe in detail all the mountains and rivers of America.

Though Darwin and Pavlov differed in their methods, temperaments, and personalities, they were alike in their qualities of thoroughness, consistency, and patience in collecting facts on which to base their principles. Their ability to listen to the voice of nature, whether expressed in life or through the planned laboratory experiment, their capacity for laborious accumulation of data, their scientific zeal, their insight, their establishment of scientific laws by the facts—these are reasons why they both are foremost pioneers in the long procession of scientific explorers throughout the ages.

NOTES

¹ The phrase "battle for the mind," though dramatizing the struggle for a scientific and objective point of view, perhaps gives the wrong slant. It is more properly a battle for the right of scientific investigation of what is available to "scientific methods," even if these are phenomena usually dealt with exclusively by subjective and vague formulations.

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