Lectures on Conditioned Reflexes: Twenty-Five Years of Objective Study of the Higher Nervous Activity (Behaviour) of Animals

Pavlov argues that the higher nervous activity of animals—learning, discrimination, inhibition, and even what we call temperament—can be studied objectively as a system of reflexes, without recourse to subjective psychology or mentalistic explanation. He rejects the introspective method that had dominated the study of mind, proposing instead that the cerebral hemispheres be investigated with the same physiological methods applied to digestion or circulation. The conditioned reflex, in which a previously neutral stimulus acquires the power to elicit a response through pairing with an unconditioned stimulus, is the basic unit of this objective analysis. Pavlov positions his work as a strictly physiological account of behavior, not a psychological one.

W. Horsley Gantt, an American physician who worked in Pavlov's laboratory in Leningrad from 1925 to 1929, translated and edited the lectures with the collaboration of G. Volborth [citation:1][citation:2]. The first volume was published by International Publishers in 1928, with an introduction by Walter B. Cannon of Harvard [citation:1]. The translation was made from the third Russian edition of Pavlov's Twenty-Five Years of Experience, with five new chapters added by the author specifically for the English edition [citation:1][citation:16]. A second volume, Conditioned Reflexes and Psychiatry, followed in 1941, containing Pavlov's writings from 1928 until his death in 1936 [citation:1][citation:14]. Gantt's translation became the standard English presentation of Pavlov's work for decades.

Pavlov's method was objective in that it recorded only observable events: the presentation of stimuli and the measured secretion of saliva from a surgically prepared fistula . No inferences were made about what the dog thought, felt, or intended. This contrasted sharply with the introspective psychology that dominated the late nineteenth and early twentieth centuries, which relied on trained observers reporting their own mental contents. Pavlov argued that the subjective method was hopeless as a scientific approach because mental states are accessible only to the person experiencing them. His alternative was to treat behavior as a physiological process, subject to laws of excitation and inhibition that could be studied in the same way as any other bodily function. This stance made his work foundational for later behaviorism, though Pavlov himself resisted being classified as a psychologist .

Pavlov's lectures develop the concept of internal inhibition, a process by which conditioned responses are suppressed when the conditioned stimulus is repeatedly presented without the unconditioned stimulus. He argues that internal inhibition is not merely a passive decay but an active nervous process, subject to laws of irradiation and concentration across the cerebral hemispheres. He extends this analysis to sleep, proposing that sleep is a state of widespread inhibition spreading over the cortex—the same process that, when localized, produces the extinction of a conditioned response [citation:13]. This unification of inhibition, sleep, and hypnosis under a single physiological mechanism was one of Pavlov's most influential theoretical moves, shaping subsequent research on the neural basis of arousal and attention.

The book was greeted with enthusiasm by many prominent scientists. John B. Watson, the founder of behaviorism, wrote that Pavlov's work 'will be of tremendous help to American scholarship' and that 'the behaviorists in this country have the most profound respect and affection for him because his work made behaviorism definite and concrete' [citation:9]. H. G. Wells called Pavlov 'a star which lights the world.' Harvey Cushing described it as 'a great book by one of the world's greatest living scientists' [citation:9]. However, a 1942 review in Nature of the second volume was more critical, noting that the collection of general articles was repetitious and that the translation was 'obscure and clumsy,' though the reviewer praised the final chapter—written the year before Pavlov's death—as the most complete and orderly presentation of his work [citation:4].

Conditioned Reflexes (1927), translated by G. V. Anrep, was Pavlov's systematic monograph on the conditioned reflex, presenting a coherent and orderly account of his laboratory findings. Lectures on Conditioned Reflexes (1928) is a collection of lectures and papers delivered over more than two decades, tracing the historical development of his work from its beginnings in 1903 [citation:13]. The lectures are more repetitious and less systematic than the 1927 monograph, but they contain material not found elsewhere, including Pavlov's reflections on the reflex of purpose, the reflex of freedom, and the application of his findings to psychiatry. Together the two books provided the English-speaking world with complementary access to Pavlov's work: one a definitive statement, the other a developmental record.