Integrative activity and the role of cortical neurons
Cerebral cortex neurons take direct part in the regulation of complex behavioral acts. This involvement can occur either throughout the entire action or during its distinct, strictly specific stages.
A fundamental concept in this topic is neuronal integrative activity. It represents the unique ability of a cell to receive and process arrays of information of completely different modalities and subsequently generate its own excitation.
The significance of this activity lies in the fact that each individual neuron makes its own unique contribution to the overall, global excitation system of the brain. This is how an integrated adaptive behavioral act is formed. The spike activity recorded in cortical neurons reflects two crucial aspects:
- Symptom-temporal and probabilistic parameters of the environment.
- The organism's own attitude toward this environment, including attempts at its active and targeted transformation.
Dynamics of behavioral act formation
Behavioral formation during learning goes through several regular stages, each characterized by a specific set of afferent (incoming) signals.
- Baseline level (in an untrained animal). At the initial stage, the foundation is formed by motivational excitation (internal need) and situational afferentation (signals arriving from various sensory organs regarding environmental conditions).
- Learning process. As the skill is acquired, feedback afferentation (reverse afferentation) is invariably added to the baseline structure. This is the flow of information that informs the nervous system about the parameters of the ongoing movement, allowing for its correction.
- Achievement of the result. Successful completion of the action leads to reinforcement. Physiologically, this stage is always accompanied by a pronounced emotional evaluation and naturally leads to sharp fluctuations in the initial level of motivational excitation (typically, its decrease upon the satisfaction of a need).
Experimental model and timeline
To study brain activity, behavior is broken down into clear temporal stages. A classic example is the food-acquisition behavior of a cat in an experimental chamber:
- Stage I: The animal presses a special pedal.
- Stage II: The moment milk appears in the feeder (direct reinforcement).
- Stage III: The animal begins to lap the milk.
During the experiment, researchers record the discharge activity of neurons. It can be presented as a single activity graph during a single behavioral act (type A) or as summary histograms. In the latter case, neuronal activity is averaged over 10 performances of the act (types B, C, D), which makes it possible to identify reliable patterns.
Neurochemical basis: pharmacological analysis
The recruitment of neurons into a behavioral act occurs exclusively via chemical pathways. This is proven by the method of microiontophoresis, which allows for the targeted delivery of neurotransmitters to a cell and the assessment of changes in its activity pattern.
The neuron under investigation demonstrated a characteristic increase in spike activity under normal conditions (control), strictly starting from the moment the pedal was pressed.
- Effect of acetylcholine: Microiontophoretic application of this neurotransmitter led to the abolition of the discharge at the moment of pedal pressing (at stage I) and a substantial decrease in spike activity during the reinforcement itself (at stages II and III).
- Effect of norepinephrine: The application of norepinephrine caused a general, non-selective decrease in the baseline activity of the nerve cell. This inhibitory effect was consistently observed at all stages of food-acquisition behavior without exception (both before and after pressing the pedal, and during food consumption).
Briefly: answers to topical questions
Which central neurotransmitters are involved in the formation of motivational excitation?
Motivational excitation is formed by complexes of various neurotransmitter systems rather than isolated individual mediators. The following systems are involved in this process:
- Adrenergic system — participates in specific chemical integration within brain structures.
- Cholinergic system — is involved in the formation of various motivations.
- Dopaminergic system — integrates with other substances to create a specific motivational state.
The complexity of the neurochemical organization lies in the fact that neurotransmitters work in various combinations, pooling together into a specific motivational state.
What stages are included in the central architecture of the functional system of behavior according to P.K. Anokhin?
The central architecture of the functional system of behavior includes four successive nodal stages. According to P.K. Anokhin's concept, these are:
- Afferent synthesis — the stage of selection and comparison of excitations, including dominant motivation, situational afferentation, and memory.
- Decision making — the nodal moment of switching from synthesis to a specific action program.
- Action result acceptor — the apparatus for anticipating the required result and evaluating the future outcome.
- Efferent synthesis — the stage of program implementation.
To evaluate behavioral outcomes, the system also utilizes the feedback afferentation mechanism.
To memorize the components forming the behavior of a trained animal, use the mnemonic rule: Motivation — Situation — Feedback (movement parameters) — Reinforcement (result and emotion).
Class and exam questions
What is neuronal integrative activity?
This is the ability of a nerve cell to receive and process information of various modalities, followed by the generation of its own action potential (excitation).
What components form the basis of an untrained animal's behavior?
The foundation is formed by motivational excitation and situational afferentation arriving from sensory organs.
What accompanies the achievement of a result in a behavioral act?
It serves as reinforcement, which is accompanied by an emotional evaluation and leads to fluctuations in the level of motivational excitation.
How does norepinephrine affect the spike activity of a neuron in the described experiment?
It causes a general decrease in the baseline activity of the cell at all stages of behavior, including periods before pressing the pedal and during food consumption.
What else to study on this topic
- Methodology for constructing summary histograms in the analysis of a series of behavioral acts
- Symptom-temporal parameters of the environment and their coding in the cortex
- Changes in the sensitivity of the neuronal receptor apparatus to neurotransmitters during the learning dynamics
- Mechanisms of feedback afferentation in the correction of complex movements
- Microiontophoresis technique in studying the neurochemical basis of behavior
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