Chemical specificity of motivations

Connection of emotions, learning, and appetite

Each motivation is experienced subjectively and accompanied by a specific emotional reaction. The biological significance of such experiences is that they allow an individual to quickly and reliably assess their needs without resorting to detailed analysis. Subjective experiences associated with metabolic needs are always negative in character. Their main task is to stimulate the search for objects to satisfy the need.

In their pure form, negative emotions accompany the need only in the early stages of ontogenesis or upon its initial appearance. Further behavioral shaping is closely linked to the learning mechanism:

• Repeated satisfaction of the need elicits positive emotions.
• An animal or a human remembers these sensations.
• Positive emotions begin to weave into the structure of motivational excitation on an anticipatory basis.

This is how appetite arises—the subject's anticipation of the positive emotion that will occur upon satisfying the current need. Appetite is a powerful stimulus for goal-directed activity. The expectation of a "reward" forces one to act more actively, overcome obstacles more successfully, and determines the selective direction of motivation.

What is the chemical specificity?

From the perspective of electrophysiology, motivational excitations of different biological quality (e.g., hunger, thirst, or fear) are characterized by completely identical changes in the electrical activity of brain structures—the so-called EEG activation.

However, each motivation possesses distinct specificity, which manifests in emotional sensations, features of cortico-subcortical integration, and, most importantly, in chemical mechanisms. Neuropharmacological analysis using selective blockers proves that different motivations rely on different mediator systems:

• Defensive motivation (fear) is selectively suppressed by $\alpha$-adrenoblockers (e.g., aminazine). This fact was established in studies by V.A. Gavlicek and A.I. Shumilina.
• Feeding motivation (hunger) is selectively blocked by cholinolytics (atropine, amizil).

Experimental evidence

Chemical selectivity is clearly demonstrated in classic animal experiments.

Conflict of motivations (rabbit experiment) A rabbit is trained to eat in a specific room. Then, in the same setting, it is subjected to electrocutaneous stimulation. As a result, a conflict arises: despite severe hunger, the fear motivation dominates. The rabbit refuses food and cowers in the corner. However, if aminazine is administered intravenously (0.5 mg/kg), the adrenergic mechanisms are blocked. Fear is instantly eliminated, the previously suppressed feeding motivation is disinhibited, and the rabbit immediately begins to eat. This proves that hunger and fear are built on different chemical pathways.

EEG analysis (cat experiment) After two days of food deprivation, a cat is placed under urethane anesthesia. On the EEG in the anterior cortical regions, a selective "hunger" activation is observed, whereas slow activity typical of narcotic sleep is recorded in the temporo-occipital regions. If nociceptive (pain) stimulation is applied, generalized activation of the entire cortex occurs.

• Administration of aminazine blocks only the pain-induced activation, without affecting the "hunger" activity of the anterior regions.
• Administration of cholinolytics eliminates exclusively the activation associated with hunger.

Pharmacological agents make it possible to perform a peculiar "chemical dissection" of ascending subcortical influences on the cerebral cortex.

Complexity of neurochemical organization

The mechanisms of chemical specificity are significantly more complex than the primitive scheme of "one neurotransmitter — one motivation." Experiments demonstrate high variability of reactions: cholinolytics block hunger not in all animals, just as adrenolytics do not always eliminate fear.

According to V.G. Zilov's concept, entire complexes of various systems (adrenergic, cholinergic, dopaminergic) are involved in the formation of motivations. This holds true for both feeding motivation (upon stimulation of the lateral hypothalamus) and defensive motivation (upon stimulation of the ventromedial hypothalamus).

Conclusion: Chemical specificity is determined not by a single specific substance, but by a specific chemical integration of physiologically active substances. Neurotransmitters combine into unique combinations across different brain structures, forming a concrete, unique motivational state.

Class and exam questions

What else to study on this topic

• Functions of the lateral and ventromedial hypothalamus in behavioral regulation
• Mechanisms of cortico-subcortical integration in the formation of motivations
• Theory of functional systems and the role of anticipatory reflection of reality
• Neuropharmacological analysis of ascending activating influences of the reticular formation
• The role of the dopaminergic system in positive emotion formation and the reward system

Other topics in the "Motivations" section

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