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Physiology of Memory

For medical students2 min readUpdated 2026-10-10

The foundation of memory is the organism's ability to form acquired behavioral programs to adapt to the external environment. Unlike rigid instincts, these programs are flexibly restructured based on conditioned signals, past experience, and continuous evaluation of the probability of obtaining reinforcement.

Essence of adaptationSelection and retention in memory of the most reliable conditioned signals leading to the goal.
Role of reinforcementWithout reinforcement, the conditioned signal loses significance, and behavior is restructured.
DynamismBehavioral programs are easily modified when external conditions change.
Action acceptorThe neural apparatus that anticipates the properties of the result and the means of achieving it.

Distinction Between Acquired Experience and Instincts

Acquired behavioral programs differ fundamentally from innate instinctive activity (such as the behavior of the Sphex wasp). The main difference lies in flexibility: relying on memory, the animal responds to leading conditioned signals that immediately direct it toward reinforcement.

In a formed skill, intermediate stage results that are not essential for satisfying the dominant drive are simply ignored. The organism does not need to reproduce the entire chain of actions from scratch every time if the shortest path to a useful result is already fixed in memory.

Stages of Adaptive Activity Formation

The process of learning and information consolidation in memory can be analyzed using the example of a puppy's feeding drive in an unfamiliar room:

  1. Initial entry into the environment. Genetic mechanisms are triggered: feeding motivation and an orienting-exploratory reaction. The animal actively explores all objects via trial and error. At this stage, absolutely all stimuli encountered on the way to food are recorded in memory.
  2. Behavioral programming. From the array of recorded information, only the most significant stimuli (e.g., the room setting) are selected. These become the leading signals.
  3. Re-entry into the same environment. Behavior changes radically. The animal rushes directly to the place where it previously found food, using the mechanism of a conditioned reflex. Intermediate inedible objects no longer elicit exploratory interest.

Thus, only those stimuli that are reliably associated with obtaining reinforcement acquire special significance.

Behavior in a Changing Environment

If external environmental conditions change frequently and haphazardly, and reinforcement becomes unstable, the initial spatial stimuli lose their signaling value. In such cases, the organism is forced to switch its orientation to new, more reliable signals.

A dynamic behavioral program always includes two components:

According to classical physiological concepts, it is the presence of reinforcement that determines whether a signal retains its significance in individual life.

General Patterns and Systemogenesis

The formation of acquired behavior obeys three main patterns:

The process of improving so-called systemquants of behavior during learning is called systemogenesis. It affects the nodal stages of system architectonics: the formation of the action acceptor and efferent synthesis.

Interestingly, somatovegetative support does not remain static during this process—it changes predictably across stages of skill acquisition, automation, and extinction. If living conditions become stable and periodically repeating, a dynamic stereotype begins to form in the organism.

Frequently asked questions

What types of memory are distinguished in physiology based on information retention time?

Based on temporal characteristics, three main types of memory are distinguished:

  • Short-term memory — retains information from several seconds to a few minutes after presentation. It provides brief storage of content in consciousness after the disappearance of initial sensory impressions.
  • Intermediate memory — retains information for several minutes or hours.
  • Long-term memory — unlimited in capacity and duration of information storage. It provides the conscious recall of past events and sensations.
Which brain structures are responsible for memory consolidation?

The process of memory trace consolidation is associated with the deep structures of the temporal lobes and the limbic system.

The hippocampus plays a paramount role in ensuring consolidation (the transition of short-term memory to long-term memory) and the stabilization of conscious memory. Furthermore, the integrity of the structures forming the Papez circuit (hippocampus, mammillary bodies, anterior thalamic nuclei, cingulate gyrus) is essential for proper encoding and transfer of information into long-term memory. Bilateral damage to these regions impairs memory fixation.

What are the cellular mechanisms of synaptic plasticity during learning?

Cellular mechanisms of synaptic plasticity are triggered upon the convergence of stimuli at the neuronal membrane.

This activates a cascade of biochemical reactions (second messengers), and the signal is transmitted to the cell nucleus. The nucleus undergoes genome activation and immediate-early gene expression: de novo synthesis of specific proteins is initiated via transcription and translation.

These synthesized proteins are incorporated into synaptic membranes or alter the neuronal structure. As a result, long-term potentiation occurs at the synapses that participated in the successful action, ensuring long-term fixation of the connection and the formation of an engram.

What happens to a conditioned signal if it ceases to be reinforced?

In accordance with memory mechanisms, the signal gradually loses its significance, undergoes inhibition, and the animal begins searching for new, more reliable cues to satisfy its dominant drive.

What is the main difference between acquired and instinctive behavior?

Acquired behavior is flexible and allows skipping non-essential stages of past experience, reacting immediately to leading conditioned signals that lead to the goal. Instincts, by contrast, require rigid reproduction of the entire chain of actions.

What is the role of orienting-exploratory activity?

It allows the retrieval of necessary genetic programs and previously acquired skills to successfully satisfy dominant needs in a completely new, unfamiliar environment.

What is the systemogenesis of behavioral acts?

It is the process of improving behavioral systemquants during learning, which enriches the programming apparatus (action acceptor) and refines the effector apparatus.

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