Excerpts from Lectures on Conditioned Reflexes, Volume II: Conditioned Reflexes and Psychiatry
Ivan Petrovitch Pavlov
Introduction by W. Horsley Gantt
World War II provided medicine with rare opportunities for studying the breakdown of normal persons subjected to intense stresses. In England at the time of the Normandy invasion in June, 1944, special arrangements had been made to deal with a new crop of acute military and civilian neuroses resulting from this operation. One day while travelling to an emergency neurosis centre, soon after the start of the invasion, I stopped at an American neuro-psychiatric hospital to visit a colleague, Dr. Howard Fabing. He had just been reading a book by the famous Russian neuro-physiologist I. P. Pavlov, called Conditioned Reflexes and Psychiatry, and strongly advised me to do the same at once. This book consisted of a series of lectures given by Pavlov not long before his death in 1936 at the age of eighty-six; but they had not become available in English until 1941. Stocks of the translation had been destroyed in the London Blitz that same year, but Dr. Fabing had managed to secure a copy. Like several other neuro-psychiatrists of World War II, he had found Pavlov’s observations on animals extremely useful for the better understanding of certain behaviour patterns observed when human beings break down under abnormal stress.
Pavlov’s clinical descriptions of the ‘experimental neuroses’ which he could induce in dogs proved, in fact, to have a close correspondence with those war-neuroses which we were investigating at the time. Also, many of the physical treatments that had gradually been developed by trial and error during the war to relieve acute nervous symptons, had obviously been anticipated by Pavlov as a result of his prolonged research on dogs. It was now clear that what was needed was a much more careful study of certain of these findings, in their possible relation to human psychiatry, than had recently been given them either in England or in America. William Sargent, Battle for the Mind, Pan, London, 1957, pp. 14-15.
Pavlov’s applications of his concepts to psychiatry in the last decade of his life were based upon his previous experimentations with dogs. An analogy was made between the symptoms obtained in the laboratory with those seen in patients. By this method he thought that he was able to illuminate the origin and development of the several forms of human psychoses, particularly schizophrenia, hysteria, obsessions and paranoia. The observations upon which his deductions were based concerned first, his four constitutional types or temperaments – those in which excitation predominated (choleric, sanguine) and those in which inhibition predominated (phlegmatic, melancholic). The central group which did not ordinarily break down included the sanguine and the phlegmatic – both, however, stable, well-balanced animals. The extreme groups, choleric and melancholic were liable to a breakdown either in the direction of excessive excitation or excessive inhibition.
As causes of the experimental neurosis Pavlov considered not only the type of animal (heredity), but the situation (environment), the chief elements of which had to do with the method of giving the conditioned stimuli involving a “collision between the excitatory and inhibitory processes.” In Vol. I of Lectures on Conditioned Reflexes Pavlov described the experimental neurosis, or disturbance of behaviour in the animals; entailing a so-called collision of the excitatory and inhibitory processes. In the present volume he showed that, in addition to collision, an excessively strong excitatory stimulus would also produce a disturbance. The intensity of the conditioned reflex has been shown (by Gantt et al), to depend upon the intensity of the unconditioned stimulus, i.e., the motivation or emotional tension, and by Pavlov (Lyman, Kupalov, et al), to depend also upon the intensity of the conditioned stimulus – a loud bell produces a greater food excitation than a faint one. This is true within certain ranges of the intensity of the conditioned stimulus, but beyond a certain maximal intensity variations of the effect may lead to certain phases – equivalent (in which strong and weak stimuli produce the same effect), the paradoxical (in which the weak stimuli give a greater response than the strong), the ultraparadoxical (in which the excitatory conditioned stimuli become inhibitory and vice versa). Such conditioned stimuli, too strong to give the maximal conditioned reflex, Pavlov termed transmarginal or supramaximal, which I have translated here as ultramaximal.
Pavlov considered that inhibition was a protective mechanism. When the conditioned stimuli became so strong that the result produced would exceed the capacity of the given nervous system, by the foregoing law excitation became replaced by inhibition, thus protecting the weak cortical cells from excessive excitation. Underlying this explanation was the hypothesis that excitation and inhibition rested upon independent substances. Although there is little experimental evidence for such a view, in recent years an indication of its truth has been received from the experiments of Loewi, Babkin, Wolff; Stavraky on acetylcholin as a stimulus for certain peripheral nerves and the experiments of Cannon, Rosenblueth, Rioch et al on sympathin – a substance stimulating peripheral nerves having in general opposite effects to those stimulated by acetylcholin.
In dogs with a “weak nervous system” the above-described phases, particularly the ultraparadoxical, were prominent. Such animals showed negativism, stereotypy and other symptoms comparable to what is seen in the schizophrenic patient. For example, these dogs continued to make certain useless, stereotyped movements over and over again. “Negativism” was expressed by their refusal of food, when it was offered, and, on the other hand, turning toward food as it was taken away. Also some of these dogs fell into a “hypnotic” state in which there was paralysis of the motor skeletal musculature, especially of those muscles most concerned with the given excitation, i.e., those of eating. Such animals stood like marble statues, drooling at the mouth but unable to take the food. These Pavlov considered analogous to the patients, catatonics, who exhibit catalepsy and remain immobile to even painful stimuli, and consistently refuse food so that they have to be fed through the nose. Cyclism has also been seen in certain of Pavlov’s dogs, corresponding to the succession of mania and depression in human patients.
(Also) Pavlov’s honesty and methods are in general beyond criticism. He wholeheartedly admitted the existence of secretin when discovered by Bayliss though he had to modify his own theories. And this was after he had tested the results in his own laboratory – “Of course they are right; we can not aspire to the monopoly of knowledge.” He was the first to admit his error in having stated that he had proven the inheritance of acquired characteristics (conditioned reflexes).
Except for a few instances, as the above, no successful criticism has been made of Pavlov’s facts. Another example referred to the data on which the law of irradiation and concentration was built. Lashley, Loucks, and others contended that the mathematical analysis of the experiments showed that Pavlov had insufficient factual material for the laws. Hull, on the other hand, confirmed Pavlov’s results in human subjects, but gave a different explanation to the facts. As far as Pavlov’s experimental results have been tested it would seem, then, that no significant error has been found in any of the data. An explanation can be found in Pavlov’s careful, painstaking methods, his adequate controls, his habit of giving the same problem to several collaborators working in separate laboratories or institutes, with whom he checked results and supervised experiments except in the last years of his life.
Pavlov is, however, especially vulnerable to criticism in the theories, laws and deductions which he has built upon his scientifically obtained facts.
(On the other hand) Pavlov had the advantage of being easily understood and his theories are so clearly stated that they may be put to the test. The necessity of theory in science has been mentioned in the preceding pages, but a closing remark of the great English physiologist, Sir William Bayliss, is stated here in defence of Pavlov’s manner of stating theories:
As Bacon has well pointed out, truth is more likely to come out of error, if this is clear and definite, than out of confusion, and my experience teaches me that it is better to hold a well-understood and intelligible opinion, even if it should turn out to be wrong, than to be content with a muddle-headed mixture of conflicting views sometimes miscalled impartiality, and often no better than no opinion at all. Sir Wm. M. Bayliss, Principles of General Physiology, 1931, p. xviii.
Straus in his brilliant treatise on Pavlov says he, like Columbus, while not finding what he set out for, nevertheless made a great discovery.
Says a prominent American physiologist and historian:
Pavlov was indeed one of five or six individuals of the last generation who caused mankind to think in new terms; like Freud he created a new horizon, but unlike Freud he remained wholly objective in his mode of collecting scientific data. John Fulton, ‘Ivan Petrovitch Pavlov,’ New England Journal of Medicine, March 5, 1936, Vol. 214, No. 10, p. 5.
Let us then accept Pavlov at his word, admit that his imposing and clear-cut theories conveyed by the terms, concentration and irradiation of excitation and of inhibition, induction, internal inhibition and sleep, are but stepping stones, or are even beyond the pale, that they have served their day, what then remains? Granted that these should one day reach the scrap-heap, are we left emptyhanded? For generations to come every investigator in the field of physiology and more especially psychobiology may be thankful to Pavlov for having blazed a path, for having demonstrated the use of an objective method to measure important aspects of behaviour (as well as of secretion) in the intact, healthy, though restrained, animal. Pavlov’s careful elaboration of the method and the painstaking, scientific, and bold demonstration of its use will permanently elevate him to a place among the Great Scientists.
W. HORSLEY GANTT
Ivan Petrovitch Pavlov, Lectures on Conditioned Reflexes, Volume II: Conditioned Reflexes and Psychiatry, translated and edited by W. Horsley Gantt, Lawrence & Wishart Ltd., London 1941.