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"Essentially, only one thing in life is of real interest to us - our psychical experience. Its mechanism, however, was and still is shrouded in profound obscurity."

I. P. Pavlov


Ivan Pavlov was a Russian scientist most famous for describing the psychological phenomenon referred to as a "conditioned response". Pavlov made a number of other very important discoveries in the realm of physiology, particularly related to digestion. Indeed, it was while studying the secretion of digestive enzymes that he became interested in the integration of the body and the brain.


Born to a Russian minister on September 14, 1849, Pavlov grew up in the town of Ryazan. Due to a childhood accident, Ivan was unable to attend school as early as other children, but did get started at age 11. After finishing school he was sent to theological seminary to follow in his father’s footsteps, but dropped out in 1870 to enroll at the University of St. Petersburg. It was there that Pavlov became interested in and started his career in physiology.

His first research project, under the tutelage of Elie Cyon, involved investigation of pancreatic nerves, and this work earned him gold medal honors at the university. Pavlov continued his studies at the Military Medical Academy between the years of 1875 and 1879. He finished his dissertation and earned the degree of doctor of medicine in 1883. Pavlov gained the influence of prominent researchers such as Ludwig, Heidenhain, and Bofkin during the next several years, and was named Professor of Pharmacology at St. Petersburg Institute of Experimental Medicine in 1895. Soon after this honor he became Professor of Physiology, and held that position until 1924.

Pavlov's first independent work focused on the physiology of the circulation of the blood. He studied the influence of variations in blood volume on blood pressure. He also investigated the nervous control of the heart, and argued that rhythm and strength of cardiac contractions are controlled by four types of nerves. It was during this first independent study that Pavlov used unanesthetized, neurologically intact dogs. This method became the mainstay of Pavlov’s methodology.

Pavlov felt that the experimental methods used by many physiologic researchers introduced too many sources of error. In order to understand the true physiological mechanisms of an organ, that organ had to be observed as it functioned as a part of whole body:


"I would prefer to remain a pure physiologist, that is, an investigator who studies the functions of separate organs, the conditions of their activity, and the synthesis of their function in the total mechanism as a part or in the whole of the organism; and I am little interested in the ultimate, deep basis for the function of an organ or of its tissues, for which primarily chemical or physical analysis is required."

Pavlov's methodology involved training dogs to lie calmly on the operating table while he incised the skin and surface tissues, disclosed the artery, and connected it to instruments for measuring blood pressure.

Pavlov’s second independent work centered around digestion. He started studying digestion as early as 1879, and it was his major focus from 1890 to 1897. His work was an accumulation of observations on the nervous control of one organ system through the method of chronic experiment. The study of digestion involved developing "fistulas" through which secretions from salivary glands, stomach, the pancreas, and small intestine could be collected. His technique was truly unique in that he did not cut the nerve supply nor contaminate the secretions with food.

Pavlov'''s accomplishments from study of digestive organs included:

  • discovery of enterokinase, an enzyme in the duodenum that activates trypsin,

  • description of the neural control of the pancreas and pancreatic control as a response to different foods,

  • demonstration that chewing and swallowing alone would cause gastric secretion,

  • conclusion that the secretory nerve that controls the gastric glands is the vagus nerve,

  • demonstration of variance in types and amounts of secretions of the stomach is a response to different foods,

  • observation that the mere sight of food stimulates salivary and gastric secretion.

In 1897, Pavlov published his results and generalizations in a book called "Work of the Digestive Glands". For this work, he was the first Russian and physiologist to receive the Nobel Prize, which was awarded in 1904.

This last observation listed above marks the beginning of a shift of Pavlov’s research focus. He began to study the "higher mental processes", particularly the effects of sight and smell of food on salivation. He classified all the reactions of an animal as conditioned or unconditioned.

The most famous and well-known experiment of Pavlov is that he 'conditioned' dogs to initiate a salivary response to the sound of a bell. He began by measuring the amount of salivation in response to only food. As the experiments continued, he rang a bell as he presented the food. Again, he noted a salivary response. Finally, by only ringing the bell, Pavlov observed the same response as having presented food to the dogs . . . salivation. These experiments defined what has been a "conditioned response".

It is this same principle that makes our our mouths water and stomachs awaken when we smell the odors of a restaurant or see the 'golden arches' come into view.

The final 35 years of Pavlov’s research were devoted to the investigation of the conditioned reflex and the study of the brain. In the late 1920’s, he began working with clinical patients, trying to understand the qualitative differences between the higher nervous processes of animals and of people.

"Science will sooner or later bring the obtained objective results to our subjective world, and will at once illuminate our mysterious nature, will explain the mechanism and vital meaning of that which eternally occupies the human mind - it’s conscience, and it’s tribulations."


The 'conditioning' model presented by Pavlov had an enormous influence on western behavioral psychology. For Pavlov, the assumption was that the unconscious processes that existed were simple reflexes which could be conditioned to affect behavioral change.


Ivan Petrovich Pavlov can be thanked for maintaining the purity of observational science and striving to keep the standards for experimental methodology at its highest level. Although he is most remembered for his groundbreaking work in behavioral psychology, the inspiring research that led Pavlov to these observation cannot be forgotten. He was a truly great scientist and researcher.

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