Efferent synthesis and action

Action result acceptor and initiation of synthesis

In the structure of a complex behavioral act, efferent synthesis immediately follows the stages of afferent synthesis and decision-making. Its main task is the dynamic integration of central nervous system structures to prepare the executive act. The mechanism of this integration relies on intracentral feedback afferentation.

The process of action formation proceeds under the control of the action result acceptor. This apparatus maintains the initial goal through the cyclical interaction of nerve cells (reverberation of excitation). Information about actual achievements, arriving via feedback channels, is continuously compared with the programmed parameters.

According to neurophysiological studies (experiments by B.V. Zhuravlev), the anticipation of a future outcome is directly reflected in the activity of nerve cells. In the presence of dominant motivation (thirst, hunger, fear), neurons demonstrate bursting activity. As soon as the need is satisfied, their activity shifts to a regular pattern.

Behavioral action and its clinical significance

The formed action is always aimed at active interaction with the environment to obtain a biologically or socially significant result. Any behavioral act includes a complex combination of several components:

• Motor;
• Autonomic;
• Immune;
• Endocrine.

The ratio of these elements is strictly individual and depends on the current degree of emotional tension. In clinical practice and normal physiology, it is customary to distinguish two variants of action execution:

1. Adaptive variant. The subject achieves the required result without marked tension of the body's functional systems.
2. Pathogenic variant. The desired outcome is achieved at the cost of immense psycho-emotional effort. At the same time, pronounced autonomic and endocrine dysfunctions occur, which serve as a risk factor for the development of psychosomatic pathology.

Learning and memory: initial state and pathway selection

The formation of adaptive behavior and memory can be considered through the scheme of neuronal group selection. Prior to learning, the neural network is characterized by high variability and redundancy. The input neuron (stimulus source) transmits excitation through a chaotic network of intermediate interneurons to the motoneuron. Excitation spreads diffusely, there is no rigid binding of stimulus to reaction, so the initial response of the organism is exploratory or accidental.

The process of learning and selecting effective pathways proceeds in a specific sensory context—under the influence of situational afferentation (visual, olfactory, gustatory, tactile). From the entire diversity of the network, a specific group of neurons is singled out, the activity of which leads to success.

At this moment, a feedback loop comes into play, carrying a signal about the usefulness of the action (reinforcement, e.g., dopamine release). The coincidence of the sensory context, the activity of specific cells, and the reinforcement signal triggers mechanisms of synaptic plasticity. In particular, long-term potentiation (LTP) develops precisely in those synapses that provided the successful result.

Consolidation and neuronal Darwinism

The result of the learning process described above is consolidation—the formation of a stable memory engram.

After learning, a dominant pathway for signal conduction is formed. Connections between the neurons of the selected specific group are repeatedly strengthened. The phenomenon of facilitation (easier conduction) arises: upon the reappearance of the stimulus, excitation instantly follows the path of least resistance. Due to this, the behavioral act becomes automated, fast, and maximally accurate, while collateral and ineffective connections are inhibited or eliminated.

This entire scheme clearly illustrates the principle of neuronal Darwinism (selection): out of many potentially possible variants of neural connections, under the influence of outside information and reinforcing signals, the most adaptive neural circuit is selected and rigidly fixed.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• The role of excitation reverberation in short-term memory mechanisms and goal maintenance
• Individual variability of the components of the executive act under emotional tension
• Mechanisms of synaptic plasticity and long-term potentiation (LTP) during learning
• The influence of situational afferentation on the selection of neural pathways
• The connection between the pathogenic variant of action and the development of psychosomatic pathology

Other topics in the section "Systemic architectonics of behavioral acts"

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