Question 1 How is conditioned reflex formed?

The most common conditioned reflex is food salivation conditioned reflex. Feeding dogs can cause saliva secretion, which is an unconditional reflex; Food is an unconditional stimulus. Listening to the bell for dogs will not cause saliva secretion, and the bell has nothing to do with saliva secretion, which is called irrelevant stimulation. But if you listen to the bell before feeding the dog every time, after many combinations, when the bell appears, the dog will have saliva secretion. At this point, the bell has become a signal of eating (unconditional stimulation), which is called signal stimulation or conditional stimulation. Salivation caused by isolated conditioned stimulus (bell) is called food salivation conditioned reflex. It can be seen that conditioned reflex is acquired. The basic condition of conditioned reflex is the combination of unconditional stimulus and irrelevant stimulus in time, which is called reinforcement. After any unconnected stimulus is combined with unconditioned stimulus for many times, when unconnected stimulus is transformed into conditioned stimulus, conditioned reflex is also formed. If unrelated stimuli are combined with unconditional stimuli that cause animal body movements many times, defensive motor conditioned reflex can be formed. Some conditioned reflexes are complex and require animals to complete certain operations. For example, mice get food by accidentally stepping on the lever in the experimental box. If this process is repeated many times, mice will learn to automatically step on the lever and get food. On this basis, further training, only when a certain signal (such as light) appears, you can get food by stepping on the lever. After many intensive trainings, animals can get food by stepping on a lever when they see a specific signal (light). This kind of conditioning is called operant conditioning. Its characteristic is that animals can only be strengthened by some kind of movement or operation. After the conditioned reflex is established, if the conditioned stimulus is repeatedly applied without unconditional stimulus, the conditioned reflex will gradually weaken and finally disappear completely. This is called conditioned reflex regression. For example, combining ringtones with food many times has established a conditioned reflex in dogs; Then, if the bell is repeatedly applied without food (without reinforcement), the saliva secretion caused by the bell will gradually decrease, and finally it will not cause secretion at all. The regression of conditioned reflex is due to the fact that the conditioned stimulus that originally caused saliva secretion turned into the stimulus that caused cerebral cortex inhibition without reinforcement. The regression of conditioned reflex is not the loss of conditioned reflex, but the conditioned reflex that causes excitement (salivation) becomes the conditioned reflex that causes inhibition (no salivation). The former is called positive conditioned reflex and the latter is called negative conditioned reflex. In the process of organism life, conditioned reflex can be established continuously, but some conditioned reflex has subsided due to the change of environment, and some new conditioned reflex has been established to make animals better adapt to the change of environment.

Question 2. What is the mechanism of conditioned reflex?

The mechanism of conditioned reflex formation is not completely clear. Some people think that the establishment of conditioned reflex is the temporary connection between conditioned stimulus focus and unconditioned stimulus focus after many combinations in the cerebral cortex. But this kind of promotion cannot be proved by experiments. At present, it is believed that the establishment of conditioned reflex is related to many parts of the center, among which the reticular structure of brain stem and cerebral cortex play an important role. The condition of conditioned reflex involves four things, two of which are stimuli and two are physical reactions. One is neutral stimulation, which will not cause the expected response that needs to be learned before conditioned reflex is formed. This is conditioned stimulus (CS), which is the bell in Pavlov's experiment. The second stimulus is unconditional stimulus (UCS). Can cause the expected reaction before the formation of conditioned reflex: before the formation of conditioned reflex, meat, namely UCS, appears, causing saliva secretion. The response of saliva secretion to unconditional stimulus is called unconditional response (UCR). This is a reaction that will occur before any degree of conditioned reflex is formed. The reaction started by conditioned reflex is called conditioned reflex (CR), that is, there is no meat, only crisp saliva secretion reaction. When the two stimuli are repeated immediately (similar in space and time), a conditioned reflex is formed. Usually, unconditional stimulus follows conditional stimulus. After conditioned stimulus and unconditional stimulus appear several times, conditioned stimulus gradually causes saliva secretion. At this time, animals have conditioned reflex. Once neutral conditioned stimuli (ringtones) can now cause saliva secretion alone.

Stage 1: UCS UCR Unconditional Reflex Stage 2: UCS independently stimulates UCR

(food) (salivation) (food) (bell) (salivation)

Stage 3: CS CR conditioned reflex stage 4: CS NO UCS unconditioned stimulation.

(ringing) (salivation) (ringing) (fading) CS conditioned stimulus

The combination of neutral stimulation and unconditional stimulation in time is called reinforcement. The more reinforcement times, the more consolidated the conditioned reflex. Conditional stimulation is not limited to auditory stimulation. All effective stimuli from inside and outside the body (including compound stimuli, the relationship between stimuli and time factors, etc.). As long as it is combined with unconditional stimulus in time (that is, reinforcement), it can become conditional stimulus and form conditioned reflex. After one conditioned reflex is consolidated, another new stimulus can be combined with conditioned reflex to form a second conditioned reflex. Similarly, a third-order conditioned reflex can also be formed. In people, multi-level conditioned reflex can be established. When conditioned stimulus is not strengthened by unconditional stimulus, there will be inhibition of conditioned reflex, mainly regression inhibition and differentiation. After the establishment of conditioned reflex, if it is strengthened by conditioned stimulus for many times without unconditional stimulus, the reaction intensity of conditioned reflex will gradually weaken and eventually disappear completely. For example, dogs that form salivation conditioned reflex to bells are only given bells without food reinforcement. After many times, the amount of saliva secretion caused by Bell will gradually decrease, or even cause no secretion at all, and the conditioned reflex will also fade. Pavlov believes that regression is because the conditioned stimulus that can produce the excitement process in the cortex has now become the stimulus that causes the inhibition process, which is the transformation from excitement to inhibition. This inhibition is called regression inhibition. Pavlov pointed out that regression inhibition is an active inhibition process of cerebral cortex, not that the temporary connection between conditioned stimulus and corresponding response has disappeared or been interrupted. Because if you leave the subsided conditioned reflex for a period of time without doing experiments, you can naturally recover; Similarly, if the conditioned stimulus is strengthened again in the future, the conditioned reflex will recover quickly, which shows that the regression of conditioned reflex is not the disappearance of the temporary connection that has been formed before, but the temporary connection is suppressed. The speed of regression is generally that the more consolidated the conditioned reflex is, the slower the regression speed is; The weaker the conditioned reflex is, the easier it will fade. At the beginning of the establishment of conditioned reflex, in addition to conditioned stimulus itself, those stimuli similar to stimulus also have the effect of conditioned stimulus more or less. For example, a tone of 500 Hz is combined with eating to establish food secretion conditioned reflex. At the initial stage of the experiment, many other tones can also cause salivation conditioned reflex, but the greater the difference between them and the tone of 500 Hz, the smaller the conditioned reflex effect. This phenomenon is called conditioned reflex generalization. After that, only the conditioned stimulus (500 Hz tone) was strengthened, but the approximate stimulus was not strengthened, so the generalization reaction gradually disappeared. Animals only produce food secretion conditioned reflex to frequently intensified stimuli (tone of 500 Hz), but have inhibitory effect on other similar stimuli. This phenomenon is called differentiation of conditioned reflex.

Question 3: What is the research significance of conditioned reflex?

The importance of Pavlov's works is immeasurable. Shortly after his research was published, some psychologists, such as Watson, the founder of behaviorism school, began to argue that all behaviors were based on classical conditioned reflex. Although this extreme view is not common in the United States, Russian theory based on classical conditioned reflex once dominated the field of psychology for a long time. In any case, people agree that there are quite a few behaviors that can be well explained from conditioned reflex theory to classical conditioned reflex viewpoint. Conditioned reflex refers to two unrelated things, because when one thing appears together for a long time, it will inevitably be linked with another thing, which is the response of the body due to the stimulation of signals. For example, the bell won't make the dog drool, but if you ring the bell every time before feeding food, the dog will drool after hearing the bell several times. This reaction caused by the signal of the bell is called conditioned reflex, and the bell is called conditioned stimulus. Conditioned reflex is acquired. It is a reflection established on the basis of unconditional reflection through certain conditions in the process of life. It is the basic regulation mode of higher nerve activity, and both humans and animals have physiological activities. The basic condition of conditioned reflex is the combination of irrelevant stimulus and unconditional stimulus in time. Any combination of irrelevant stimulus and unconditioned stimulus can form conditioned reflex, which is generally believed to be realized only with the participation of cerebral cortex. Traditionally, the establishment of conditioned reflex is due to multiple simultaneous excitations between the cortical representative area of conditioned stimulus and the cortical representative area of unconditioned stimulus, resulting in a "temporary connection" in function. The excitement caused by conditioned stimulus in the cortex can reach the cortical representative area of unconditioned reflex through temporary contact, thus causing a reaction that could not have been caused. At present, the neural mechanism of temporary contact is not clear. After the conditioned reflex is established, if the conditioned stimulus is used repeatedly without the reinforcement of unconditional stimulus, the conditioned reflex will fade. In the early stage of conditioned reflex formation, conditioned reflex also appeared the phenomenon of generalization and differentiation, which is the basis for the cerebral cortex to realize complex analysis and comprehensive functions. Some conditioned reflexes can also be consolidated by heredity.