Mechanism of origin
According to the concept of I.P. Pavlov's school, the response action is based not on the initial properties of the stimulus itself, but on the fact of its repeated coincidence with unconditioned reflexes.
As an example, we can consider the formation of a food-reward reflex:
- Initial baseline: Mandatory presence of a drive (the animal must be hungry).
- First contact with the stimulus: When the conditioned stimulus is first turned on (e.g., a light turns on), innate orienting-exploratory activity occurs. The subject turns the head and torso, examining the light source.
- Repeated pairings (10–20 times): The action of the lamp is combined with feeding. As a result, a temporary connection is formed.
- Result: The external light radically changes its meaning. The exploratory reaction fades, and the light begins to elicit an anticipatory food reaction (abundant salivation and characteristic movements).
Unlike the food-reward reflex, the defensive reflex (when the signal is combined with a current shock) requires much less time: it is enough for the animal to have just 2–3 pairings of the stimulus with pain to develop a persistent avoidance reaction.
Rules for elaboration (according to I.P. Pavlov)
For the temporary connection to be successfully consolidated, strict adherence to a number of physiological conditions is required:
- Presence of motivation. The organism must be in the corresponding functional state (hunger for a food response, a feeling of fear of damage for a defensive one).
- Mandatory reinforcement. The signal makes no sense unless it ends with the satisfaction of a vital need.
- Rule of time (precedence). The indifferent signal must act on receptors earlier than the unconditioned reinforcement appears.
- Ecological adequacy and perception. The signal must be captured by sense organs and have biological meaning for a specific species. For example, changes in water composition or movement are important for fish, while sounds, smells, and light are important for higher mammals.
- Ratio of strength. The unconditioned reinforcement must be biologically more powerful than the conditioned stimulus.
- Multiplicity. Repeated repetition of the "signal + reinforcement" pair is required (law of pairing).
- Absence of competition. At the moment of learning, there should be no other dominant foci (e.g., acute pain or an overfull bladder).
- State of health. The subject must be absolutely clinically healthy.
Classification of conditioned reflexes
Conditioned reflex activity can be divided into groups according to several key criteria.
By receptor apparatus (analyzer):
- Visual (to light);
- Auditory (to sound);
- Olfactory;
- Cutaneous (tactile) and others.
By biological nature of reinforcement:
- Food-reward;
- Defensive;
- Sexual.
By time interval of reinforcement delivery:
- Short-delayed: the interval between the signal and reinforcement is from 10 to 20 seconds (maximum up to 30 s).
- Long-delayed: the pause exceeds 30 seconds.
- Trace: reinforcement is given approximately 3 minutes later.
- Trace conditioning: the reinforcing factor is delivered exclusively after the conditioned stimulus has ceased its action (excitation is superimposed on the "trace" in the nervous system).
- Simultaneous: the signal and unconditioned factor act synchronously.
Law of strength relations and higher-order reflexes
The law of strength states that the scale of the conditioned reflex response depends on the physical brightness of the stimulus (the stronger the signal, the more active the reaction) and on the biological value of reinforcement (e.g., a dog will produce more saliva to a signal reinforced by fresh meat than to meat-biscuit powder). This law can be distorted in special phase states of the organism: during sleep, hypnosis, or in neuroses.
Higher-order reflexes are formed when a new neutral stimulus is combined not with an innate reaction, but with an already firmly established conditioned reflex (first-order). This is how a second-order, and then a third-order, temporary connection is formed. In dogs, the limit of training usually ends at the third order (most easily based on defensive reactions), and it is not possible to develop a fourth-order reflex. In humans, due to verbal reinforcement, much higher-order reflexes can be formed.
Instrumental conditioned reflexes
This is a special type of adaptive behavior in which the animal must perform an active physical action (press a lever, pull a ring, assume a certain posture) to receive reinforcement.
The peculiarity lies in the fact that such motor acts are carried out reflexively. In classical experiments by N.V. Asmayan and E.M. Bogomolova, it was shown that if the pedal is moved to another place, the dog after the sound signal will still run to the old place and press the floor with its paw. The adaptive meaning of such behavior is consolidated only when the physical action itself becomes a significant intermediate stage on the way to the goal.
Briefly: answers to topical questions
What physiological mechanisms underlie the formation of a temporary connection during the elaboration of a conditioned reflex?
The formation of a temporary connection is based on the convergence of stimuli on cortical neurons and the subsequent activation of the genetic apparatus. According to I.P. Pavlov, the connection is formed in the cerebral cortex between the representation foci of the conditioned signal and unconditioned reinforcement.
At the molecular level, the following processes occur:
- Convergence of stimuli — the combination of excitations from motivation, the conditioned signal, and reinforcement on the neuronal membrane.
- Activation of intracellular processes — the launch of a cascade of biochemical reactions involving secondary messengers and signal transmission to the nucleus.
- Activation of the genome — expression of early genes and protein synthesis according to the "DNA → RNA → Protein" scheme.
- Structural rearrangement — synthesized specific proteins are incorporated into synaptic membranes or change the structure of the neuron.
These changes provide long-term plasticity and consolidation of the memory trace (engram).
What types of inhibition of conditioned reflexes exist?
The sources describe the following types of inhibition associated with conditioned reflexes:
- Active cortical inhibition — its disruption occurs when reinforcement is delayed, that is, when the interval between the conditioned signal and food delivery is increased.
- Discriminative inhibition — its disruption is caused by the elaboration of several successive subtle and complex differentiations.
- Extinctional inhibition — its breakdown occurs when reinforcement is withdrawn, i.e., in the absence of a reward for previously established conditioned reflexes.
When the inhibitory process breaks down, a neurotic state develops with a predominance of excitation in the brain due to weak inhibitory control.
Class and exam questions
What happens upon the first presentation of a conditioned signal (e.g., light)?
Initially, the organism elicits an innate orienting-investigatory reaction: it turns the head and torso toward the source of the stimulus. Only after repeated pairings with food does this stimulus become conditioned and begin to elicit a feeding reaction.
What is the time rule in reflex conditioning?
The precedence rule requires that the neutral conditioned stimulus begins to act before the unconditioned reinforcement is delivered.
What is a trace conditioned reflex?
This is a type of reflex in which unconditioned reinforcement is delivered to the animal only after the conditioned stimulus has completely ceased, meaning the reaction is formed to a neural "trace".
How does an instrumental reflex differ from a conventional one?
To receive reinforcement in an instrumental reflex, the subject must perform a specific active motor action (e.g., press a pedal), which acts as an intermediate adaptive result.
What else to study on this topic
- Inversion of the law of strength relations in hypnosis, sleep, and neurotic states
- Features of higher-order reflex development in humans based on verbal reinforcement
- Ecological significance of stimuli for different biological species
- Evidence base for the reflex nature of motor reactions (experiments with pedal displacement)
- Differences in the speed of acquisition of appetitive and defensive conditioned reflexes
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