Pavlov- CNS Conceptual nervous system

Ivan Pavlov (1849-1936) differentiated himself from boh Sechenov and Western physiology and psychiatry. He began as a digestive physiologist for 25 years, studying salivation "psychologic salivation" with various physiologic techniques and won the Nobel Priz in 1904. His trespass into psychology was deemed risky by colleagues and was criticized. BF Skinner in 1938 The Behavior of Organisms interpreted Pavlov in a way that was accepted by Konorski and Hebb. The conditioned reflex is mediated by a complex S-R (stimulus-response) with processes of modulation including excitation, inhibition and reciprocal induction. The modulatory processes of the brain were not observed but were deduced from the S-R. The central nervous system therefore was more virtual than real, and Skinner termed Pavlov's CNS as the "Conceptual Nervous System." Skinner noted that Sherrington had deduced the spinal synapse long before it was actually described, and Pavlov hoped to do analagously with the CNS.

The S-R was explained in behavioral terms , but also in neuroconceptual terms and on a third level, on neuronal terms (after observing the physiology). For example, in behavioral terms, the strength of a reflex could be reduced by presenting a second stimulus related to the effector involved. In neuroconceptual terms, the second stimulus coming by different afferents inhibits the conductivity of the impulses specific to the effector. In neuronal terms, the actual pathways are described. On a conceptual level, the importance is that the neuroconceptual models predct that eventually the entire behavior will be explained physiologically.

Pavlov was misunderstood, but stated clearly that "it was not our aim to interpret the activity of the hemispheres in terms of the elementary functions of the nervous system." Soviets misunderstood his ideas as applying to all behaviors. Western sources criticised him as well. Konorski and Hebb later accepted Pavlovian models as the models that they were.

Konoski chronologically divides Pavlov's life into periods. From 1901-1910, Pavlov elaborated phenomena of the conditioned reflex such as external inhibition, generalization, differentiation. 1910-1920, Pavlov introduced laws of dynamics of cortical processes such as irradiation, concentration, reciprocal induction. From 1920 on, Pavlov focused on processes of excitation and inhibition, types of nervous system and neurosis.

The reflex arc is a means by which animals adapt to their environments. Pavloc said investigation of the higher centers ought to be faithful to the same methods used in the lower systems. The conditioned reflex ensures the survival of the individual. Reflexes are derived from the "innate organization" of the nervous system. Instincts are complex systems of unconditioned reflexes. Conditional (conditioned, acquired) reflexes are formed by connections between centers for conditioned reflexes and centers for unconditioned reflexes. Conditioned reflexes can be suppressed, or inhibited, externally (passively or unconditioned) by something that suppresses the formation of the reflex, or internally (or actively) . It can be experimentally extinguished by withholding the conditioned stimulus. There may be a post inhibitory effect afterwards in which other CR are inhibited from being formed.

Stimuli similar to the conditioned reflex can cause excitation (generalization of the stimulus). If only one class of the stimuli are reinforced and others are not, there is differentiation of the CR. The signalling action of the reinforced stimulus (duration, intensity, action, etc.) are reinforced, and other stimuli are inhibited. Inhibition of delay occurs if the stimulus is produced a few seconds after the conditioned stimulus, then the action occurs a few seconds later as well. Transmarginal inhibition occurs if some feature of the CS eg intensity, fatigues the nervous system and prevents the formation of the normal CR.


The dynamics of the reflex are interactions between excitatory and inhibitory processes. Expansion of excitation to adjacent parts of the nervous system is called irradiation, and then focus at the point where it continues to have an action is called concentration. These 2 functions depends on characteristics of the stimulus especially intensity. In sleep, inhibition irradiates through the CNS and dominates the "equilibrium."

The law of reciprocal induction refers to the fact that around an area of excitation there is a zone of inhibition (negative induction), and vice-versa (positive induction forms around an area of inhibition). The analyzer is the functional unit of the receptor and cortical projections that analyse a stimulus. Pavlov counted five sensory analyzers, plus a motor analyzer. The cortex was an analyzer-synthesizer without specific specialization. The analyzers all communicated with each other, but communicated best to other analyzers in close proximity.

Pavlov rejected therefore the idea current in neurology of cortical centers, and of physiologists such as Bekhterev that cortical centers existed. Pavlov thought CR operated through subcortical centers. Pavlov used lesion studies to "show" the "diffuse" nature of the cortical analyzer which was the "law of equivalence of all the parts of the hemispheres from the functional point of view."

In the last period of his life, Pavlov studied the principal properties of the nervous system, including the strength of the excitation and inhibition, the mobility, and the equilibrium between the two. Strength was the ability to react strongly to a CR, the mobility referred to adaptability to different types of stimuli, and equilibrium was whether there was an equal capacity to deliver positive or negative reflexes. Subjects could be typed into strong subjects (easy to form CR) and weak subjects (hard to form CR) and by balanced (equivalent ability to form positive or negative reflexes) or unbalanced. The latter if inert, could never form CR, if mobile they could adapt and perhaps be able to do so.

For a number of years in the USSR, the Pavlovian precepts were accepted in an orthodox manner, uncritically. Later, Westerners and USSR scientists such as Konorski explored them critically. In 1949, Donald Hebb published The Organization of Behavior that discussed the use of physiological models for behavior processes. His concepts of "cell assemblies" borrowed heavily from Pavlov. His book was influenced by Lorente de No's work on reverberating circuitry. Integration of behaviorism and neurophysiology continued with Pribham "neurobehaviorism" and Razran "brain-behaviorism."