In the activity of the nervous system I.P. Pavlov distinguished the following: the activity aimed at regulating the work of individual organs and on the integration of all parts of the body, which he called the lower activity. Activity that establishes the connection of the organism with the external environment and the finest adaptations of the organism to the external world was called by I.P. Pavlov as the higher nervous activity. All the parts of the central nervous system work according to the principle of reflex. But the cerebral cortex along with the unconditioned reflexes of the central nervous system, common to all parts, is capable of carrying out a second kind of reflexes, called by I.P. Pavlov as conditional ones. A conditioned reflex is the reaction of the body to a conditioned, signal stimulus, which is developed during life and requires certain conditions for its occurrence. Conditional reflexes are formed when two foci of excitation arise in the cortex of the brain: one - in response to the action of the conditioned stimulus, and the other - to the action of the unconditioned stimulus. When a combination of the action of these stimuli occurs, there is a temporary connection between the emergent foci of excitation, which fbecomes more and more stable with exerience. I.P. Pavlov called this connection in the cerebral cortex as a closure, and explained the mechanism of formation of the conditioned reflex (Figure 4.1). 

 

4.1 Conditional reflexes, as the basic form of activity of the cerebral hemispheres

The purpose of the lesson: get acquainted with the method of formation of conditioned reflexes according to Pavlov.

The following is necessary for work: dog, dog bed frame, electric bell, electrostimulator with electrodes, physiological saline and scissors, equipped cage, rooster, grain, kymograph, electric meter, stopwatch, special spectacle frame for giving a trickle of air to the subject's eye, electric bell, stopwatch.

 

Work 1 Development of a defensive conditioned reflex in a dog

Work progress: The dog is placed on the bed frame, the strap with the electrodes is fixed on the area of the metatarsus. The threshold strength of the stimulus is found, and then the power is increased so that it causes a distinct rise of the paw and the experiment starts (Figure 4.2).

In the beginning, a conditioned signal is given and after 5 seconds from the start of the action, the induction current is turned on for 10 seconds. The conditioned signal is switched on for 15 seconds. Both stimuli are turned off at the same time. The combination is repeated after 1 minute, until one call induces the motor-defensive reaction.

 

Work 2. Conditioning in a rooster

Conditional reflexes in birds are produced in a special cell. In the plywood wall of the cell, a conditioned stimulus 1 and a rotating feeder 2 are mounted.  A thin plate of organic glass is fixed above the feeder in the tilted position 3, which almost completely covers the cup of the feeder and blocks access to the food. Contacts 4 of the direct current electric circuit are mounted on the underside of the plate. If the plate is lightly pressed, it easily moves and opens the cup. In this case, the circuit closes and the marker 5 makes a mark on the kymograph. When the pressure on the film ceases, it immediately returns to its original position.

Work progress: The rooster is put in a cage.   Some grain are put in the cup of the feeder, and the plate is first removed so that it does not prevent the rooster from pecking the grain. Then the plate is returned to the working position and the rooster is tamed to peck the grain, pushing the plate aside. When the rooster gets used to pecking the grain from the cup, covered with a plate, one can proceed to the elaboration of conditioned reflexes.

The conditioned stimulus is turned on and after 2-3 seconds a up with grain is pushed out. The duration of the action of the conditioned stimulus is 10-15 seconds; the interval between stimuli is 2 minutes. During the experiment, no more than 15-20 combinations of a conditioned stimulus with an unconditioned one are given. During the experiment movements of the rooster are recorded on the kymograph.

 

Work 3. The development of a conditioned blinking reflex to a call in humans.
        Work progress: The subject wears a spectacle frame. The experimenter, pressing on the pear, checks that a trickle of air gets into the eye of the subject and leads to a flashing without causing any painful sensations. Turn on the electric bell for 5 seconds without pressing the pear, and make sure that the blinking reflex to the bell is not observed.
        Then they proceed to develop a conditioned blinking reflex on the bell. Turn on the bell for 5 seconds. After 1-2 seconds after turning on the bell, an air jet is applied until the ringing sound is completed. The combination of stimuli is repeated 7-12 times with an interval of at least 1 minute.
After 7-12 combinations turn on the bell, without giving a trickle of air to the eye. If the sound of the bell is flashing, then the conditioned blinking reflex to the bell has already been worked out. If there is no blinking, then the combination of the two stimuli is repeated until a conditioned reflex is developed. A note is made of how many repetitions of combinations of two stimuli a conditioned blinking reflex to the bell has developed.

 

Control questions

• What refers to higher division of the central nervous system?
• What is the basis of the activity of the cerebral cortex?
• Methods for studying the function of the cerebral cortex?
• The mechanism of formation of the conditioned reflex?
• Biological significance of the conditioned reflex?
• Conditions necessary for the formation of a conditioned reflex?
• Types of inhibition in the cerebral cortex