تـــــقرير عن عالم النفسي بافــــلوف جاهز- انكــــليزي

Name: Ivan Petrovich Pavlov
Birth Date: September 26, 1849
Death Date: February 27, 1936
Place of Birth: Ryazan, Russia
Place of Death: Russia
Nationality: Russian
Gender: Male
Occupations: physiologist
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The Russian physiologist Ivan Petrovich Pavlov (1849-1936) pioneered in the study of circulation, digestion, and conditioned reflexes. He believed that he clearly established the physiological nature of psychological phenomena.

Ivan Pavlov was born in Ryazan on Sept. 26, 1849, the son of a poor parish priest, from whom Pavlov acquired a lifelong love for physical labor and for learning. At the age of 9 or 10, Pavlov suffered from a fall which affected his general health and delayed his formal education. When he was 11, he entered the second grade of the church school at Ryazan. In 1864 he went to the Theological Seminary of Ryazan, studying religion, classical languages, and philosophy and developing an interest in science.

Making of a Physiologist

In 1870 Pavlov gained admission to the University of St. Petersburg (Leningrad), electing animal physiology as his major field and chemistry as his minor. There he studied inorganic chemistry under Dmitrii Mendeleev and organic chemistry under Aleksandr Butlerov, but the deepest impression was made by the lectures and the skilled experimental techniques of Ilya Tsion. It was in Tsion's laboratory that Pavlov was exposed to scientific investigations, resulting in his paper "On the Nerves Controlling the Pancreatic Gland."

After graduating, Pavlov entered the third course of the Medico-Chirurgical Academy (renamed in 1881 the Military Medical Academy), working as a laboratory assistant (1876-1878). In 1877 he published his first work, Experimental Data Concerning the Accommodating Mechanism of the Blood Vessels, dealing with the reflex regulation of the circulation of blood. Two years later he completed his course at the academy, and on the basis of a competitive examination he was awarded a scholarship for postgraduate study at the academy.

Pavlov spent the next decade in Sergei Botkins laboratory at the academy. In 1883 Pavlov completed his thesis, The Centrifugal Nerves of the Heart, and received the degree of doctor of medicine. The following year he was appointed lecturer in physiology at the academy, won the Wylie fellowship, and then spent the next 2 years in Germany. During the 1880s Pavlov perfected his experimental techniques which made possible his later important discoveries.

In 1881 Pavlov married Serafima Karchevskaia, a woman with profound spiritual feeling, a deep love for literature, and strong affection for her husband. In 1890 he was appointed to the vacant chair of pharmacology at the academy, and a year later he assumed the directorship of the department of physiology of the Institute of Experimental Medicine. Five years later he accepted the chair of physiology at the academy, which he held until 1925. For the next 45 years Pavlov pursued his studies on the digestive glands and conditioned reflexes.

Scientific Contributions

During the first phase of his scientific activity (1874-1888), Pavlov developed operative-surgical techniques that enabled him to perform experiments on unanesthetized animals without inflicting much pain. He studied the circulatory system, particularly the oscillation of blood pressure under various controlled conditions and the regulation of cardiac activity. He noted that the blood pressure of his dogs hardly varied despite the feeding of dry food or excessive amounts of meat broth. In his examination of cardiac activity he was able to observe the special nerve fibers that controlled the rhythm and the strength of the heartbeat. His theory was that the heart is regulated by four specific nerve fibers; it is now generally accepted that the vagus and sympathetic nerves produce the effects on the heart that Pavlov noticed.

In the course of his second phase of scientific work (1888-1902), Pavlov concentrated on the nerves directing the digestive glands and the functions of the alimentary canal under normal conditions. He discovered the secretory nerves of the pancreas in 1888 and the following year the nerves controlling the secretory activity of the gastric glands. Pavlov and his pupils also produced a considerable amount of accurate data on the workings of the gastrointestinal tract, which served as a basis for Pavlov's Lectures on the Work of the Principal Digestive Glands (published in Russia in 1897). For this work Pavlov received in 1904 the Nobel Prize in physiology or medicine.

The final phase of Pavlov's scientific career (1902-1936) was primarily concerned with ascertaining the functions of the cerebral cortex by means of conditioned reflexes. Prior to 1900, Pavlov observed that his dogs would secrete saliva and gastric juices before the meat was actually given to them. The sight, odor, or even the footsteps of the attendant were sufficient to trigger the flow of saliva. Pavlov realized that the dogs were responding to activity associated with their feeding, and in 1901 he termed such a response a "conditioned reflex," which was acquired, or learned, as opposed to the unconditioned, or inherited, reflex. He faced a dilemma: could he embark on the study of conditioned reflexes by applying physiological methods to what was generally viewed as psychic phenomena? He opted to follow Ivan Sechenov, who considered that, in theory, psychic phenomena are essentially reflexes and therefore subject to physiological analysis.

The important lectures, papers, and speeches of Pavlov dealing with conditioned reflexes and the cerebral cortex are presented in Twenty Years of Objective Study of the Higher Nervous Activity (Behavior) of Animals: Conditioned Reflexes (1923) and Lectures on the Work of the Cerebral Hemispheres (1927). He not only concerned himself with the formation of conditioned responses but noted that they were subject to various kinds of manipulation. He discovered that conditioned responses can be extinguished--at least temporarily--if not reinforced; that one conditioned stimulus can replace another and yet produce identical conditioned responses; and that there are several orders of conditioning. In time Pavlov developed a purely physiological theory of cortical excitation and inhibition which considered, among other things, the process of sleep identical with internal inhibition. However magnificent his experiments were in revealing the responses of animals to conditioning stimuli, he encountered difficulty in experimentally proving his assertion that conditioned responses are due to temporary neuronal connections in the cortex.

In 1918 Pavlov had an opportunity to study several cases of mental illness and thought that a physiological approach to psychiatric phenomena might prove useful. He noted that he could induce "experimental neuroses" in animals by overstraining the excitatory process or the inhibitory process, or by quickly alternating excitation and inhibition. Pavlov then drew an analogy between the functional disorders in animals with those observed in humans. In examining the catatonic manifestations of schizophrenia, he characterized this psychopathological state as actually being "chronic hypnosis"--chiefly as a consequence of weak cortical cells--which functions as a protective mechanism, preserving the nerve cells from further weakening or destruction.

In Pavlov's last scientific article, "The Conditioned Reflex" (1934), written for the Great Medical Encyclopedia, he discussed his theory of the two signaling systems which differentiated the animal nervous system from that of man. The first signaling system, possessed both by humans and animals, receives stimulations and impressions of the external world through sense organs. The second signaling system in man deals with the signals of the first system, involving words, thoughts, abstractions, and generalizations. Conditioned reflexes play a significant role in both signal systems. Pavlov declared that "the conditioned reflex has become the central phenomenon in physiology"; he saw in the conditioned reflex the principal mechanism of adaptation to the environment by the living organism.

Philosophy and Outlook

Pavlov's endeavor to give the conditioned reflex widest application in animal and human behavior tended to color his philosophical view of psychology. Although he did not go so far as to deny psychology the right to exist, in his own work and in his demands upon his collaborators he insisted that the language of physiology be employed exclusively to describe psychic activity. Ultimately he envisioned a time when psychology would be completely subsumed into physiology. Respecting the Cartesian duality of mind and matter, Pavlov saw no need for it inasmuch as he believed all mental processes can be explained physiologically.

Politically, most of his life Pavlov was opposed to the extremist positions of the right and left. He did not welcome the Russian February Revolution of 1917 with any enthusiasm. As for the Bolshevik program for creating a Communist society, Pavlov publically stated, "If that which the Bolsheviks are doing with Russia is an experiment, for such an experiment I should regret giving even a frog." Despite his early hostility to the Communist regime, in 1921 a decree of the Soviet of People's Commissars, signed by Lenin himself, assured Pavlov of continuing support for his scientific work and special privileges. Undoubtedly, Soviet authorities viewed Pavlov's approach to psychology as confirmation of Marxist materialism as well as a method of restructuring society. By 1935 Pavlov became reconciled to the Soviet Communist system, declaring that the "government, too, is an experimenter but in an immeasurably higher category."

Pavlov became seriously ill in 1935 but recovered sufficiently to participate at the Fifteenth International Physiological Congress, and later he attended the Neurological Congress at London. On Feb. 27, 1936, he died.