Ilustration: Renato M. E. Sabbatini The classic experience of Pavlov is that of the dog, the bell and the salivation to the view of a piece of meat. Whenever we present to the dog a piece of meat, seeing and sniffing it and makes the animal salivate. If we ring a bell, what is the effect on the animal? An orienting reaction. It simply looks around and turns its head to look for where that sound stimulus comes from. If we repeatedly ring the bell, and immediately after show the meat and give it to the dog, after a certain number of times, simply ringing the bell provokes salivation in the animal, preparing its digestive system to receive the meat. The bell becomes a sign of the meat that will come later. The whole body of the animal reacts as if the meat was already present, with salivation, digestive secretions, digestive motricity, etc. An stimulus that has nothing to do with feeding, a mere sound, becomes then capable to induce digestive modifications.

(1) coexistence in time, several times repeated, of the indifferent agent and the unconditioned stimulus (in the previous example, the sound of the bell presentation of the meat);

(2) the indifferent agent should somewhatprecede the unconditioned stimulus.

If we first give the meat and then ring the bell, the conditioned response is not established;

(3) absence of other stimuli that could induce externally caused inhibition. If we simultaneously whip the animal or splash it with cold water, we provoke inhibition, setting loose defensive reactions;

(4) in order to preserve the conditioned reflex, it is necessary to reinforce it periodically. Once the reflex is formed, the mere sound of the bell substitutes the presentation of the meat. But, if we repeatedly ring the bell without showing the meat, after a certain time the animal stops reacting with salivation and digestive secretion.

How Pavlovian Reflexology Works

Summing it up: an indifferent stimulus, combining with another stimulus capable to elicit an unconditioned reflex, produces an unconditioned answer. After some time the indifferent stimulus is capable, by itself, to provoke an answer that can, then, be considered a conditioned one. Those indifferent stimulus can come from external environment (auditory, luminous, olfatory, tactile and thermal stimuli) as well as from the internal environment (visceras, bones, joints).

The conditioned responses can be motor, secretory or neurovegetative. Voluntary or involuntary vegetative reactions can thus be conditioned. We can make those involuntary responses appear, at our will, if we use the appropriate conditioning. The conditioned responses can be excitatory (with function increase) or inhibitory (with function decrease).

There are several examples of physiological modifications in animals and in human beings through conditioning. We will mention just a few of them , in order to try to understand what could happen in the very moment of a placebo effect.

Modification of the Physiology Through Conditioning

A rectal catheter is inserted in a dog and through it a saline enema is injected. The presence of that liquid inside the intestine provokes, after some time, an increase in the diuresis in order to correct hydroelectrolitic the balance. After some sessions of administering the saline enema through the rectal catheter, the mere introduction of the catheter, without the enema, also provokes diuresis increase. Likewise if a dog hears a whistle before receiving an insulin injection, the hypoglycemia due to the insulin action will appear, after some time, just by hearing the whistle. The metabolism of the animal changes and it begins to answer with hypoglycemia to sound stimuli that, in normal conditions, do not act on the carbohydrate metabolism.
 

The Central Nervous System and the Conditioned Reflexes

To Know More

• Ivan Petrovich Pavlov: The Nobel Prize of Physiology or Medicine 1904 (The Nobel Foundation)
• Ivan Pavlov and Classical Conditioning (University of Indiana)
• Basic Concepts on Classical Conditioning (Universität Würzburg)

Júlio Rocha do Amaral, MD - Júlio Rocha do Amaral, MD – Teacher of clinical pharmacology, anatomy and physiology. Medical Manager of Merck S/A Indústrias Químicas (pharmaceutical and chemical industries). Redactor of didactic manuals on anatomy, physiology and pharmacology used by Merck S/A. Editing supervisor of the following scientific publications: Senecta, Galenus and Sinapse. Redactor of clinical trials and protocols since 1978. Assistant coordinator of courses on Oxydology sponsored by the Human Being Institute  and UNIGRANRIO (University of Great Rio). Head of Psychiatric Service. Neurosciences Department. The Human Being Institute. Co-author of the book "Principles of Neurosciences" Email: julioamaral@pobox.com

Renato M.E. Sabbatini, PhD. holds a doctorate in neurophysiology of behavior by the School of Medicine of the University of São Paulo at Ribeirão Preto. He was visiting scholar at the Max Planck Institute of Psychiatry, Munich, Germany. Currently, Dr. Sabbatini is associate director of the Center for Biomedical Informatics and associate professor and Chairman of Medical Informatics of the Medical School of the State University of Campinas, Campinas, Brazil. Associate Editor of Brain & Mind. Email: sabbatin@nib.unicamp.br