Ivan Pavlov

1849-1936
Russian physiologist and Nobel laureate best known for his development of the concept of the conditioned reflex, or conditioned response.

Ivan Pavlov was born into an impoverished family in the rural village of Ryazan, Russia. He won a government scholarship to the University of St. Petersburg and studied medicine at the Imperial Medical Academy, receiving his degree in 1883. In 1890, Pavlov was appointed to a professorship at the St. Petersburg Military Academy and a few years later joined the faculty of the University of St. Petersburg. He organized the Institute of Experimental Medicine in 1895, which was to be his research laboratory for the next 40 years.

In the 1890s, Pavlov investigated the workings of the digestive system—focusing on digestive secretions— using special surgically created openings in the digestive tracts of dogs, a project strongly influenced by the work of an earlier physiologist, Ivan Sechenov (1829-1905). As a result of this research, Pavlov was awarded the Nobel Prize for Physiology and Medicine in 1904. During his investigations in this area, Pavlov observed that normal, healthy dogs would salivate upon seeing their keeper, apparently in anticipation of being fed. This led him, through a systematic series of experiments, to formulate the principles of the conditioned response, which he believed could be applied to humans as well as to animals. According to Pavlov's system, an unconditioned stimulus, such as offering food to a dog, produced a response, or unconditioned reflex, that required no training (salivation). In contrast, a normally neutral act, such as ringing a bell, became a conditioned stimulus when associated with the offering of food and eventually would produce salivation also, but as a conditioned reflex. According to Pavlov, the conditioned reflex was a physiological phenomenon caused by the creation of new reflexive pathways created in the cortex of the brain by the conditioning process. In further studies of the cortex, Pavlov posited the presence of two important processes that accompany conditioning: excitation, which leads to the acquisition of conditioned responses, and inhibition, which suppresses them. He eventually came to believe that cortical inhibition was an important factor in the sleep process.

Pavlov continued working with conditioned reflexes throughout the early decades of the twentieth century, generating several addition principles through further experimentation. The principle of timing dictated that the neutral stimulus must precede the unconditioned reflex in order to become a conditioned stimulus. (In other words, a buzzer would have to go off before food was offered to a dog in order for the dog to associate the food and buzzer with each other). The concept of extinction referred to the fact that a conditioned response could be "unlearned" if the neutral stimulus (buzzer) was repeatedly used without reinforcement (food). Generalization was the name given to the observation that a stimulus similar to the conditioned stimulus would still produce a response as the dog generalized from its original experience to a similar one, but the response would be less pronounced in proportion to the difference between the stimuli. Finally, testing the limits of the dogs' ability to differentiate among stimuli led, unexpectedly, to experimental

Ivan Pavlov (right of center) with his staff and one of his laboratory dogs. (The Bettmann Archive. Reproduced with permission.)

neuroses, similar to mental breakdowns in humans, when the subjects were forced to confront conflicting or ambiguous stimuli for any length of time. Observing the ways in which neurotic symptoms differed among test subjects led Pavlov between 1916 and 1936 to formulate a theory of four different types of temperament linked to physiological differences based on differences in excitatory and inhibitory activity. Attempting to extend the implications of this theory to human psychopathology, Pavlov helped establish the Soviet Union's continuing tradition of organically-based psychiatric treatment.

Pavlov, who died of pneumonia in 1936, tried to apply his ideas to psychiatry, and was influential enough to be considered one of the founders of Russian psychiatry, and he remains a dominant figure in Russian psychology. Although he never considered himself a psychologist, Pavlov's ultimate belief in conditioning as the fundamental unit of learning in humans and animals provided one of the cornerstones of the behaviorist school of psychology in the United States. It is ironic that, although Pavlov was a staunch critic of communism, in the late 1920s Joseph Stalin (1879-1953) chose Pavlov's work as the basis for a new Soviet psychology. Pavlov's books include Lectures on the Work of the Principal Digestive Glands (1897), Lectures on Conditioned Reflexes (1928), and Conditioned Reflexes and Psychiatry (1941).