Action Acceptor and the Initiation of Synthesis
Within 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 CNS structures to prepare for an executive act. The mechanism of this integration relies on intracentral feedback afferentation.
The process of action formation proceeds under the control of the action acceptor. This neural apparatus maintains the initial goal through ring interactions of nerve cells (reverberation of excitation). Information about real achievements, arriving via feedback channels, is continuously compared with programmed parameters.
According to neurophysiological studies, the anticipation of a future outcome is directly reflected in the activity of nerve cells. In the presence of a dominant motivation (thirst, hunger, fear), neurons demonstrate burst activity. As soon as the need is satisfied, their activity shifts to a regular pattern.
Behavioral Action and Its Clinical Significance
A 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, two variants of action execution are distinguished:
- Adaptive variant. The subject achieves the required result without marked strain on the body's functional systems.
- Pathogenic variant. The desired outcome is achieved at the cost of immense psychoemotional effort. This is accompanied by pronounced autonomic and endocrine dysfunctions, serving as a risk factor for psychosomatic pathology.
Learning and Memory: Initial State and Pathway Selection
The formation of adaptive behavior and memory can be viewed through the framework 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 a motoneuron. Excitation spreads diffusely with no rigid binding of stimulus to reaction, so the initial response is exploratory or random.
The process of learning and selecting effective pathways occurs within a specific sensory context—under the influence of situational afferentation (visual, olfactory, gustatory, tactile). Out of the network's diversity, a specific group of neurons whose activity leads to success is selected.
At this moment, a feedback loop carrying a signal of action utility (reinforcement, such as dopamine release) is triggered. The coincidence of the sensory context, specific cell activity, and reinforcement signal triggers mechanisms of synaptic plasticity. Specifically, long-term potentiation (LTP) develops precisely in those synapses that ensured a successful outcome.
Consolidation and Neuronal Darwinism
The result of the learning process described above is consolidation — the formation of a stable memory engram.
Post-learning, a dominant pathway for signal conduction is established. Connections between neurons of the selected specific group are repeatedly strengthened. The phenomenon of facilitation (ease of conduction) arises: upon re-exposure to the stimulus, excitation instantly follows the path of least resistance. Consequently, the behavioral act becomes automated, rapid, 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 neural connection variants, the most adaptive neural circuit is selected and rigidly fixed under the influence of external information and reinforcing signals.