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A learned response performed by a trained animal to a signal that was previously associated with an event of consequence for that animal. Conditioned reflex (CR) was first used by the Russian physiologist I. P. Pavlov to denote the criterion measure of a behavioral element of learning, that is, a new association between the signal and the consequential event, referred to as the conditioned stimulus (CS) and unconditioned stimulus (US), respectively. In Pavlov's classic experiment, the conditioned stimulus was a bell and the unconditioned stimulus was sour fluid delivered into the mouth of a dog restrained by harness; the conditioned stimulus was followed by the unconditioned stimulus regardless of the dog's response. After training, the conditioned reflex is manifested when the dog salivates to the sound of the bell.
Ideally, certain conditions must be met to demonstrate the establishment of a conditioned reflex according to Pavlov's classical conditioning method. Before conditioning, the bell conditioned stimulus should attract the dog's attention or elicit the orienting reflex (OR), but it should not elicit salivation, the response to be conditioned. That response should be specifically and reflexively elicited by the sour unconditioned stimulus, thus establishing its unlearned or unconditioned status. After conditioned pairings of the conditioned stimulus and the unconditioned stimulus, salivation is manifested prior to the delivery of the sour unconditioned stimulus. Salivation in response to the auditory conditional stimulus is now a “psychic secretion” or the conditioned reflex.
To this day, Pavlov's methods provide important guidelines for basic research upon brain mechanisms in learning and memory. Scientists all over the world have paired a vast array of stimuli with an enormous repertoire of reflexes to test conditioned reflexes in representative species of almost all phyla, classes, and orders of animals. As a result, classical conditioning is now considered a general biological or psychobiological phenomenon which promotes adaptive functioning in a wide variety of physiological systems in various phylogenetic settings. See Cognition, Memory
conditioned reflexan automatic response which has been trained or learnt. A reflex response is a naturally occurring response to a stimulus, for example, salivation is the natural response to the stimulus of food, while the knee jerk is the natural response to a tap below the knee. However, Pavlov (1911) demonstrated that if a neutral stimulus is associated with the natural stimulus, this neutral stimulus becomes conditioned and will alone evoke the response. This response is then called a ‘conditioned reflex’ (see CONDITIONING). The paradigm is useful in explaining faulty learning, especially of fear responses, i.e. the development of phobias.
Reflexes are automatic, often involving emotional responses, not only of fear, but also of anger, pleasure or other emotions. Many human emotional responses can be seen to have developed as a result of conditioning through previous experiences. The term conditioned response is now used in preference.
an acquired, complex adaptive reaction of an animal or man; it is caused by a specific condition (hence its name) and is based on a temporary association between a conditioned stimulus (signal) and an unconditioned reflex act that reinforces the stimulus. Conditioned reflexes are caused by the activity of the highest areas of the central nervous system—the cerebral cortex and the subcortex; they occur during the process of ontogeny and are based on unconditioned reflexes.
The term “conditioned reflex” was introduced in 1903 by I. P. Pavlov. Pavlov’s research led him to devise the conditioned-reflex theory of animal and human behavior, as well as a new theory of brain functions that focused on the physiology of higher nervous activity. The study of the formation and characteristics of conditioned reflexes has furthered knowledge of the brain’s functioning.
Among the many techniques used for studying conditioned reflexes the best known is the method of the salivation reflex, which facilitates a simple and accurate evaluation of conditioned reflexes according to the extent of their development. Although modern electrophysiological, neurochemical, and psychopharmacological methods of analyzing the brain’s activity have provided much new information on conditioned reflexes, Pavlov’s original theories, based on the study of the salivation reflex, remain the foundation for research in the field.
A conditioned stimulus may be any change in the external or internal environment that is received by the body’s receptors. During a conditioned reflex’s initial, or generalization, stage an identical reaction can occur in response to many signals. Later, the conditioned reflex becomes stronger, more specialized, more selective, and more regular in magnitude. Only one signal out of many, or those stimuli that are similar to the signal, are then able to evoke an adequate reaction. If the conditions governing the formation of a conditioned reflex are disrupted, the reflex changes its parameters or disappears.
Variability, which is the most characteristic feature of a conditioned reflex, ensures the body’s adjustment to the external environment. A conditioned signal that gives incorrect information on the external environment ceases to be a stimulus for responsive behavior, and the reaction to such a signal disappears. This phenomenon is based on internal inhibition, which causes a sensitive discrimination among stimuli according to their physiological and biological properties and which helps the body dispense with conditioned reflexes that are no longer biologically useful.
Internal inhibition, which occurs during even the most highly conditioned responses, is the basis of the classification of all conditioned reflexes as either positive or negative. During positive (reinforced) conditioned reflexes, the conditioned signal causes stimulation and specific physiological activity, for example, feeding. In negative (unreinforced) conditioned reflexes, such activity is suppressed owing to the development of internal inhibition.
Depending on the stimulus causing the reflex, conditioned reflexes are classified as either natural or artificial. Natural conditioned reflexes are evoked by the inherent properties of an unconditional reinforcement that have biological significance for an animal, for example, the sight and smell of food. Artificial conditioned reflexes are evoked by stimuli that are initially unconnected to a reinforcement, for example, a bell, a light, or the sound of a metronome.
Conditioned reflexes, in conformity with the biological significance of the unconditional reinforcement, may be food-related (connected with the procurement, intake, and assimilation of food) or protective (defensive). Conditioned reflexes are also classified as autonomic or motor reflexes, according to the nature of the response.
Conditioned reflexes are further differentiated according to the structure of the conditioned stimuli, the relationships between the time required for the action of the conditional and unconditional components, the nature of the reinforcement, and the time that elapses between the signal and the response. These four factors determine the classification of conditioned reflexes into first-order reflexes, based on unconditional reflexes; second- and third-order reflexes, which originate in previously developed temporary relationships; imitative reflexes, in which the behavioral reactions of another animal serve as the reinforcement; associative reflexes, which occur when a conditioned reflex is evoked by two simultaneous indifferent stimuli; and instrumental reflexes, which help an animal procure food or which free it from such unpleasant sensations as pain. During a given type of conditioned reflex the response to the signal does not reproduce the reaction from which the response was developed.
A relatively high level of organization of the central nervous system is a prerequisite for the development of a conditioned reflex; individually acquired forms of behavior in invertebrates are not regarded as conditioned reflexes. True conditioned reflexes occur only in vertebrates: fishes, amphibians, reptiles, birds, and mammals. Higher-order conditioned reflexes are of a complexity that corresponds to the organism’s level of neural organization. In dogs, fifth- and sixth-order conditioned reflexes may be produced, and in monkeys, tenth- through 12th-order reflexes. Man, with his ability to think abstractly, can develop conditioned reflexes of the 20th order or higher. Examples of such complex reactions are the operation of various apparatus and machines, the performance of other types of manual labor, and the motor activities associated with speech.
The analysis and synthesis of stimuli from the external and internal environments are continually perfected during conditioned-reflex activity. The analysis of stimuli consists of the discrimination and separation of signals and of the differentiation in their effects on the body. The synthesis of stimuli is manifested in the association, generalization, and combination of stimuli that originate in different parts of the cerebral cortex owing to the interaction between individual neurons and groups of neurons. The analysis and synthesis of stimuli are interconnected and proceed in a parallel manner; they constitute the main function of the brain. An example of the analytic and synthetic activity of the cerebral cortex is the formation of the dynamic stereotype, which combines several temporary interactions into a functional system. The cortex fixes the order of the stimuli and of their corresponding reactions; this facilitates the cortex’s efficient functioning during the performance of a stereotyped succession of reflexes.
Conditioned reflexes are produced as a result of the closure of the neural link between two simultaneously stimulated parts of the brain. Pavlov’s conclusions about the cortical-closure mechanism of conditioned reflexes have been confirmed by detailed analysis of the neural mechanism of the conditioned-reflex link. This analysis has been based on accurate modern techniques of electroencephalography and the study of evoked potentials and of neuron activity.
According to P. K. Anokhin, the action of conditioned and unconditioned stimuli is accompanied by a generalized activation of the cortex with a subsequent convergence of increasing stimuli in certain neurons. As a result of the interaction on the cellular level between current and former processes of stimulation, temporary associations develop and are established. Every conditioned reflex is based on a system of neuron groups that is capable of reproducing traces of former stimuli in response to a signal. It was originally believed that the excitation from one group of cortical cells which receive this signal is transmitted to another group only along the horizontal nerve fibers that pass through the cortex. However, further research by the Soviet physiologists E. A. Asratian, I. S. Beritashvili, A. B. Kogan, M. M. Khananashvili, and N. Iu. Belenkov has indicated that a new functional connection may occur in a different way: from the cortex to the subcortex and back to the cortex. In addition to the cortex, many subcortical structures, including the reticular formation, the hippocampus, the basal ganglia, and the hypothalamus, contribute to the development of conditioned reflexes.
The development and establishment of a conditioned reflex are accompanied by the formation of a reflex arc, consisting of afferent, central, and efferent areas. Information on the results of a completed action enters the brain by means of feedback.
To a great extent, the multiplicity of conditioned reflexes in animals determines their complex behavior. Conditioned reflexes facilitate an organism’s adaptation to the environment. By means of many indirect signs that acquire the significance of signals, an animal obtains advance knowledge about food or impending danger and adjusts its behavior accordingly. The development of a higher-order conditioned reflex is the synthesis of two temporary connections; during this synthesis there is inhibition in the central and efferent areas of the reflex arc of the original conditioned reflex. The afferent area of the arc, however, becomes involved in the newly developed reflex. Higher levels of integration occur in an analogous way. Asratian’s hypothesis that the development of complex behavioral acts from conditioned reflexes is an integrative process proceeds from a belief that individually acquired behavioral acts are the products of reflex action.
The principles of both elementary and complex conditioned reflexes are the same for animals and man. This leads to a conclusion that is important in terms of natural science and philosophy: that the human brain obeys general biological laws and may be studied objectively. At the same time, the human brain’s activity is qualitatively unique, and its conditioned-reflex activity differs fundamentally from that of animals. This difference is caused by the presence of two signal systems in man.
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