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Whereas Ivan P. Pavlov (1849-1936) is well-known for his work on classical conditioning, his contribution to neuroscience, particularly his interest in the function of neural centers in the central nervous system, is not as widely known. During the last three decades of his life, Pavlov explored cortical processes by salivary reflex conditioning, a method he used to develop his theory of higher nervous activity. This theory outlined the function of the brain in higher organisms in their interaction with the changing environmental contingencies. As early as 1908, Pavlov outlined a neurophysiological theory as the physiological basis of his theory of higher nervous activity. He maintained that the neural processes of excitation and inhibition irradiate and concentrate among the cortical neural centers. Most of all, he emphasized the plasticity of the cortex in higher organisms' in the Darwinian struggle for existence.

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In 1929 Viktor P. Protopopov began to replicate E. L. Thorndike's animal experiments on habit acquisition. To determine the conditions necessary for habit formation, Protopopov used the natural experiment method, in which dogs encountered environments that prevented them from reaching a stimulus-bait. Not all dogs acquired the behavior necessary for obtaining the bait. Explaining the results within the framework of the Pavlovian theory of higher nervous activity, Protopopov concluded that habits were acquired when an active animal provoked by a bait-stimulus encountered an environmental barrier. The dogs tried a series of phylogenetic behaviors until the stimulus-bait was reached. The latter movements were retained, forming an ontogenetic habit. The dogs also learned not to produce the unsuccessful movements. In accord with the Pavlovian theory, individual differences in habit formation were related to temperament types. A critique of the Thorndikian Law of Effect is provided in terms of the Pavlovian theory of higher nervous activity.

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A Scientific Session of the USSR Academy of Sciences and the USSR Academy of Medical Sciences met in 1950 in Moscow, to comply with the order of I.V. Stalin to institutionalize the theory of higher nervous activity of I.P. Pavlov. This Scientific Session decreed that annual scientific conferences should be held to consider problems related to Pavlovian physiology. In response to this call, a session on the Physiological Teachings of the Academician I. P. Pavolv on Psychiatry and Neuropathology was convened in Moscow in 1951. Certain influential Soviet psychiatrists - V.A. Giliarovski, M.O. Gurevich and A. S. Shmarian were condemned for adhering to anti-Marxist ideology and to psychiatric theories conceived by Western psychiatrists. The named psychiatrists acknowledged the correctness of the accusations, admitted their errors, and promised in the future to follow Pavlov's teachings on psychiatry. The session's Presidium urged the development of a New Soviet Psychiatry based upon experimental and clinical findings and consistent with the Pavlovian conceptualization of higher nervous activity, which considered pychiatric and neurotic syndromes in terms of the dynamic localization of the brain's functions. Long-range consequences of the 1951 session are considered.

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Pavlov became interested in the nature of voluntary movements after receiving Konorski and Miller's letter in 1928 describing their experiments on conditioning of motor movements in dogs. Their paradigmatic experiment involved presenting an indifferent stimulus, followed by passive raising of the dog's leg and then reinforcement. If the same stimulus was provided during a number of trials, the animal lifted its corresponding leg. In 1928 Pavlov asked his students to condition motor movements in his laboratory. Although their findings were equivocal, Pavlov incorporated the so-called voluntary movements into his theory of higher nervous activity. Voluntary movements were responses to external environmental contingencies. On the cortical level, the motor analyzer's cells had both afferent and efferent functions. In Pavlov's view, the motor analyzer's cells established connections with the afferent cells of other sensory analyzers. Pavlov held that motor movements, as responses to external and internal environments, give humans the illusion of voluntary behavior.

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I. P. Pavlov claimed that the mind-body problem would ultimately be resolved by empirical methods, rather than by rational arguments. A committed monist, Pavlov was confronted by dualism in the case of an hysterical person. Under normal conditions, her body's left side was insensitive to pain, but when she was hypnotized, there was a reversal of her sensitivity to pain, with the right side becoming insensitive. Pavlov acknowledged that the divergence between stimulation and response suggested dualism, yet condemned his disciple G.P. Zelenyi as well as Charles S. Sherrington, for their dualistic tendencies. Pavlov's continuous adherence to monism it attributed to the influence of popular scientific books that he read during his adolescence. The books maintained that science was based upon monism. Pavlov proposed that by introducing the concept of emotions, an hysterical person's condition could be explained within the framework of his theory of higher nervous activity, thereby obviating the need to change his paradigm.

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In 1950, Stalin and the Soviet Government prevailed upon the USSR Academy of Sciences and the USSR Academy of Medical Sciences to organize the 1950 Joint Scientific Session for the purpose of formalizing the teachings of I.P. Pavlov. During the Session, some of Pavlov's erstwhile students--the Pavlovians--split into accusers and accused. The more prominent of the latter were denounced for deviating from the orthodox Pavlovian path, and urged to admit their mistakes, to work within the framework of Pavlov's theory of higher nervous activity, and to avoid Western influence. Within this context, the travail of the prominent Pavlovian physiologist L. A. Orbeli is discussed. Contemporary Russian historians and scientists, evaluating the consequences of the 1950 Joint Scientific Session, point out its negative effects; namely, the general moral decline of Soviet physiologists pressured to accept a dogmatic ideology, the lowering of the quality of research in physiology, and the self-imposed exclusion of Soviet physiology from the worldwide scientific community.

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Two Warsaw medical students, Jerzy Konorski and Stefan Miller, having read I.P. Pavlov's works on conditional reflexes, informed him in a 1928 letter that they had discovered a new type of conditioning. A previously neutral stimulus preceded the passive lifting of a dog's paw which then was followed by feeding; this stimulus then evoked the spontaneous raising of that paw. Pavlov responded informing them that their conditioning of motor responses expanded his theory of higher nervous activity, but that their conditioning paradigm-that they named CRII-did not differ fundamentally from the Pavlovian conditioning paradigm. The replication of the Warsaw experiment in Pavlov's laboratory failed to provide unequivocal results. From 1931 to 1933, Konorski, working in Pavlov's Leningrad laboratory, further explored the parameters of CRII. Pavlov insisted that the conditioning of motor movements differs from the conditioning of other sensory analyzers only in that, on the neural level, the motor analyzer is both afferent, that is, perceptive, and efferent, that is, responsive. Konorski was not convinced, and he subsequently maintained that the two conditioning paradigms were fundamentally different.

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About 1880, Rudolf Heidenhain, then Professor of Physiology and Histology at the University of Breslau, experimentally studied hypnotic phenomena. Heidenhain explained hypnosis physiologically, in terms of cortical inhibition. Subsequently, I.P. Pavlov, who in 1877 and again in 1884 was Heidenhain's student at Breslau, encountered hypnotic phenomena during conditional reflex experiments. In 1910, Pavlov described hypnotic states and explained them (as had Heidenhain three decades earlier), in terms of partial inhibition of the cortex. As the concepts of inhibition and excitation are cornerstones of Pavlov's theory of higher nervous activity, it is of historical interest to search for influences that led Pavlov to incorporate the concept of inhibition into his theory. It is most likely that Pavlov first encountered the concept of central inhibition in the 1860s when reading I.M. Sechenov's The Reflexes of the Brain (1863/1866) and that the importance of the concept was augmented by Heidenhain's use of it in explaining hypnotic phenomena.

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In 1934, I. P. Pavlov conceptualized paranoia within his theory of higher nervous activity. The conceptualization was based on the case study method used in the Psychiatric Clinic where Pavlov observed five cases diagnosed by psychiatrists as paranoid states. Furthermore, experiments with dogs as subjects produced behaviours that appeared analogous to paranoiac characteristics observed in the clinic. Pavlov's paranoia theory did not differ much from Ernst Kretschmer's 1927 explanation of the formation of paranoia. Hereditary predisposition and traumatic life experiences make, according to Pavlov, some centres in the brain more active than nearby areas, which results in preoccupation with certain ideas. Imbalance between neural excitation and inhibition creates a condition where weak external stimuli produce strong reactions, which explains paranoiac overreaction to the feeling of inferiority. Some suggestions as to Pavlov's interest in paranoia are offered.

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David Joravsky (1989) alleges that Ivan Petrovich Pavlov's theory of higher nervous activity fails to explain "most forms of complex behavior" because establishment of second-order and third-order chains of conditional reflexes was not feasible. Yet, Pavlov (1951a), relying on experimental evidence, some of which is presented, held that the interaction of higher organisms with the external environment was based on the dynamic stereotype, that is, on the integration in the cortical hemispheres of neural traces coming from the external and internal environments. In its formulation in the 1930s, Pavlov's theory was dynamic, not associative. It postulated the synthesis of conditioned reflexes, not associative chains of conditioned reflexes.

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The Pavlovian principle of strength assumed that the magnitude of the conditional response is a linear function of the intensity of the external conditional stimulus. But experiments failed to provide evidence for the universality of the principle. The Pavlovians tried to identify conditions that distorted the linearity of this relationship. Some of the disturbing conditions were external and some were internal intervening variables. It is possible that the relation between the strength of the conditional stimulus and the magnitude of the conditional response is not linear but logarithmic. Pavlov acknowledged the lack of experimental evidence to support the principle of strength in its original form.

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The life of the mentally disturbed in psychiatric institutions during the first decades of the nineteenth century has been many times described by psychiatrists connected with those institutions. The accuracy of these accounts is, however, difficult to ascertain because independent testimonies are rare. Yet, such material on the conditions at the Psychiatric Section of Charité Hospital in Berlin, which was at that time Prussia's leading psychiatric institution, is extant. This material pertains to the criminal trial proceedings against Ernst Horn, the Second Director at Charité, who in 1811 was charged with malfeasance and negligent homicide in the treatment of a mentally disturbed patient. The materials describe the daily routine of the patients as well as the therapeutic procedures - both occupational therapy and the application of noxious agents. Consideration of the conditions and therapeutic treatments of the mentally disturbed at this time is important because these were the formative years of institutionalized psychiatry which have to some extent, influenced practices during the rest of the century.

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Pavlov's aim was to use the salivary conditioning method to investigate the function of the brain of higher animals in their adaptation to the external environment. The salivary reflex, according to Pavlov, was of minor biological significance but a good indicator of the subtle changes in the brain under different experimental conditions. To account for conditioned reflex phenomena, Pavlov faced two alternatives: to offer an objective (physiological) or a subjective (psychological) explanation. In 1901, after a bitter conflict with his disciple A. T. Snarskiy, Pavlov chose the first alternative. During the next decades, Pavlov provided reasons for this decision: The physiological approach (a) avoids anthropomorphizing or speculations about the dogs' subjective experiences, and (b) permits the explanation of observed phenomena which the subjective method is not capable of doing. Pavlov realized that the conditioned reflex method has a limitation; it cannot be used in the study of human subjects because their thinking interferes with experimental results.

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In 1923, Pavlov criticized the Marxist theses and the policy of the Soviet regime. In 1924, N.I. Bukharin, a Marxist theoretician and member of the Soviet government, responded to Pavlov's passionate speech with a sarcastic diatribe. I suggest that Pavlov's speech and Bukharin's article represent a conflict between a scientist critical of the Marxist pseudotheory and a journalist's abusive response to the realization that his theory was without much merit.

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This paper examined D. Joravsky's (1989) hypothesis that I.P. Pavlov dogmatically refused to acknowledge that classical conditioning can be mediated by subcortical regions of the large cerebral hemispheres. Decortication literature from 1901 to 1936 was reviewed. The early studies available to Pavlov, who died in 1936, showed that decortication does not allow the establishment of new or retaining of old conditional reflexes (CRs). G.P. Zelenyi's later experiments(1930) suggested that the establishment of primitive CRs in decorticated dogs was possible. Pavlov never denied this possibility but cautioned that Zelenyi's experiments could have been methodologically flawed. Although Joravsky's original hypothesis on Pavlov's position on the relation between decortication and the establishment of CRs is by and large accepted, it must be stressed that Pavlov's theory of higher nervous activity was primarily concerned with the function of the brain in the higher organism's struggle for existence. Within this context the cortical, rather than subcortical, processes play the decisive role in the organism's adaptation to the changing external environment.

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Introductory texts in psychology create the misleading impression that I. P. Pavlov was concerned solely with conditioned reflexes. In fact, influenced by Woodworth's Contemporary Schools of Psychology (1931), Pavlov also became interested in learning. Pavlov proposed a two-factor learning theory according to which all learning was based on association, but conditioning and trial and error learning had specific functions. According to Pavlov, conditioned reflexes were temporary and unstable and therefore more flexible in the interaction of higher organisms with the changing environment. Trial and error learning provided knowledge and was relatively more stable. Scientific discovery was based on facts obtained by trial and error; valid relations were reinforced by experimental results, whereas incorrect relationships were extinguished. Some suggestions are made that would allow authors of introductory texts to describe more informatively the contributions of Pavlov to modern psychology.

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In the late 1920s, the Viennese psychoanalyst Paul Schilder, after performing a conditioning experiment with human subjects, criticized I. P. Pavlov's concept of "experimental neurosis." Schilder maintained that subjective reports by conditioned human subjects were more informative than the objectively observed behavior of conditioned dogs. In 1932, Pavlov published a rejoinder to Schilder's critique in the Journal of the American Medical Association. Pavlov maintained that Schilder misunderstood the value and implications of the scientific, objective method in the study of experimental neurosis. In 1934, Schilder subjected Pavlov's theory of higher nervous activity to an incisive critique in a 1935 article in Imago. Schilder objected to Pavlov's narrow, reductionist conceptualization of the conditional reflex. Schilder reiterated his view that the psychological, subjective explanation of the conditional reflex is preferable to the physiological, objective explanation, and that the inference of cortical phenomena from experimental findings might be improper. Neither Pavlov nor any of his disciples replied to Schilder. The author provides an apology for the Pavlovian position, suggesting that Schilder was unfamiliar with early and late writings of Pavlov.

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Ivan P. Pavlov's youthful relations with parents and siblings, formal education, and social activities in Riazan' are described. The Pavlovs, a highly achievement-oriented family descending from a lowly serf, improved their social status by serving the Russian Orthodox Church. Pavlov, the son of a priest, studied in the 1860s at the Riazan' Ecclesiastic Seminary for priesthood. The turbulent 1860s' decade was a period of social and political reforms. Western ideas and science were introduced to Russia. The ambitious and idealistic I.P. Pavlov was influenced by popular essays written by the journalist D.I. Pisarev, the works of the German physiologist J. Moleschott, the English writer G.H. Lewes, the German zoologist C. Vogt and the physiologist M.I. Sechenov. Losing his religious faith, Pavlov abandoned the traditional goal of becoming a priest, and, convinced that science was a road to truth and progress, left Riazan' to study natural science at the University of St. Petersburg.

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Pavlov clearly formulated his ideas on the second signal system (specifically, language) in the 1930s. This occurred in conjunction with his interest in interspecies differences and in the study of human neuroses. Pavlov proposed that conditional reflexes signal concrete reality while symbolic-language provides abstractions of reality. Phylogenetically, language emerged in the humans because this form of communication had survival value to the species. Pavlov's disciples L. A. Orbeli and N. I. Krasnogorskii had considered the ontogenetic development of language. The experimental investigation of A. G. Ivanov-Smolenskii extended Pavlov's empirical study of the function of language in psychopathology. Notwithstanding a sustained interest in language, Pavlov did not develop a theory of language acquisition based upon the conditioning principle. Pavlov's conceptualization of language may not have been original, nor did it contribute significantly to modern linguistics. It is now mainly of historical interest. It was, nevertheless, important to the conceptualization of neuroses within the context of the theory of higher nervous activity and it had far-reaching political implications for Soviet psychology in the immediate post-World War II period.

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