We are approaching the 171st anniversary (September 26th) of the birth of famous Russian physiologist Ivan Petrovich Pavlov (1849-1936). Pavlov did pioneering work elucidating the mechanism of the digestion of food for which he was awarded the Nobel Prize in Physiology or Medicine in 1904.
But he is more widely remembered for his discovery of the "conditioned reflex", work that greatly influenced the development of behaviourism in psychology. Pavlov's work is engagingly described by George Johnson in The Ten Most Beautiful Experiments (The Folio Society, 2008).
Ivan Pavlov, son of a Russian Orthodox priest, studied for the priesthood in the late 1860s. However, spurred by deep interest in the biological world and enthused by Darwin’s book On the Origin of Species, he left the seminary in 1870 and entered the University of St Petersburg to study chemistry. He concentrated on physiology, earning a doctorate of medicine in 1879.
In 1891 Pavlov was appointed head of physiology at the new Institute for Experimental Medicine. Here he used sophisticated surgical techniques to study how food is digested and absorbed by the body. Pavlov favoured the “chronic” approach in his physiological studies, where the animal, usually a dog, had its stomach, oesophagus or salivary gland manipulated under anaesthesia in order to allow fluid collection and analysis.
Observations and measurements began when the animal fully recovered from this operation. In the common “acute” approach in physiological experiments the animal was operated on in order to view some biological process in action, following which the animal was sacrificed.
To collect and analyse saliva, Pavlov relocated the opening of the duct leading to a saliva gland to the outside of the cheek, anchoring it there with a stitch. Saliva began to flow as food was placed on the dog’s tongue, lubricating the food to facilitate its passage to the stomach.
Here, and later in the duodenum, nerve sensors analyse the food signalling the body to secrete the appropriate digestive fluids needed to digest whatever the dog had eaten. After winning the Nobel Prize for this work in 1904 Pavlov moved from digestion to study “the highest parts of the nervous system”.
In his studies of digestion, Pavlov noted several things that spurred him to move on. For example, dogs would start to salivate as Pavlov approached and before food was placed on the tongue. Also, if the dog was given something unsavoury, for example mustard oil, saliva would still flow but consisted mostly of water to wash away the offensive agent and there were no gastric secretions. Salivation and stomach action were closely linked to reflexes in the autonomic nervous system.
Pavlov wanted to see if external signals could affect this process. He sounded a metronome as he gave a dog food. After a while the dog salivated on hearing the metronome, even when no food was present – previously he salivated only on seeing and/or eating the food. Pavlov called this a “conditioned reflex” to distinguish it from an “innate reflex” such as salivating at the sight of food or jerking your hand away from fire.
Innate reflexes are hard-wired, whereas the conditioned reflex must be learned. Pavlov named this learning “conditioning”. He also found the conditioned reflex is repressed if it consistently gives the wrong result – if the metronome repeatedly sounds but no food appears, the dog eventually stops salivating at the sound.
Pavlov believed that conditioned reflexes explain the behaviour of psychotic people – they withdraw from the world because they associate all stimuli with possible injury. Pavlov's discoveries opened the way for the tailored modification of behaviour and played a large role in the behaviourist theory of psychology introduced in America by John Watson in 1913.
Behaviourism holds that everything mental can be reduced to stimuli and response. It is now recognised as providing only a partial account of human behaviour but it has made significant contributions to psychology, for example behaviour modification therapy to treat certain phobias.
Lenin came to power in 1917 in Russia. Pavlov did not believe in communism and was outspoken: "For the kind of social experiment you are making I would not sacrifice a frog's hind legs." However, his world renown protected him from persecution and he worked in his laboratory until his death aged 87.
William Reville is an emeritus professor of biochemistry at UCC