ABSTRACT
Ivan Pavlov's historic discovery of the principle of the conditioned reflex was an enormous break in the scientific approach to the understanding of brain functions. Pavlov considered the secretion of saliva to the presence of food in the mouth an inborn reflex and called it an unconditioned reflex while the salivation observed to the stimuli previously neutral he called a conditioned reflex. According to Pavlov, "conditioned reflexes are phenomena of common and widespread occurrence: their establishment is an integral function in everyday life. Practically each change in the environment could become a conditioned stimulus on condition that it could be noticeable by the corresponding receptor. Manipulations with a variety of conditioned and unconditioned stimuli resulted in an accumulation of a great amount of experimental data that served as constant enrichment of the Pavlovian theory. Internal inhibition observed in Pavlov's laboratory included a form called the conditioned inhibition.
