Though our knowledge of the activity of the brain dates back to the middle of the last century and important facts about that activity had already been discovered, all those single facts did not comprise all phenomena of the highest nervous activity of the animal, and did not let us understand the physiologic mechanism of its behavior as a whole.
The systematic study of the function of the cerebral hemispheres, as an organ of the highest nervous activity of animals by the purely physiologic method of conditioned reflexes, was begun by Prof. I. P. Pavlov1 in 1901. It is known that Professor Pavlov proposed to make use of the reflex of the salivary glands as a reaction of the animal to external stimuli, and proved that this reflex, by means of the associative mechanism of the cortex, will respond to numerous external stimuli. The external stimuli could produce salivation,
KRASNOGORSKI NI. THE CONDITIONED REFLEXES AND CHILDREN'S NEUROSES. Am J Dis Child. 1925;30(6):753-768. doi:10.1001/archpedi.1925.01920180013001