Glial and Mediator Theories of Memory

Glial theory of memory

According to this concept, the formation of long-term memory directly depends on the functional activity of glial cells densely surrounding brain neurons. Glia not only provide structural support but also specifically "program" the functioning of nerve cells during learning.

Key mechanisms of glial regulation:

• Metabolic changes: During learning, the concentration of ribonucleic acid (RNA) in glial cells reliably increases.
• Synthesis of active substances: Glia begin producing specific compounds that affect neurons. These substances can alter the baseline excitability of nerve cells and significantly facilitate signal transmission across synapses.
• Myelination: According to A.I. Roitbak's hypothesis, the depolarization of neuronal membranes stimulates their active myelination by glial cells. This insulates the fiber and manifoldly increases the efficiency of nerve impulse conduction.

Mediator theory: the role of neurotransmitters

This theory is based on the premise that memory is inextricably linked to dynamic changes in synapses and shifts in the balance of neurotransmitters. Each neurotransmitter system performs its specific task.

Cholinergic system Acetylcholine is critically important for memory. Learning leads to an increase in the number of cholinergic receptors in central nervous system synapses. The microiontophoresis method proves that neuronal sensitivity to acetylcholine increases in the process. Activation of these synapses triggers conformational changes in the postsynaptic membrane, which increases conductivity. Administering acetylcholine antagonists disrupts learning and information retrieval processes, up to the development of amnesia.

Noradrenergic system Norepinephrine is sensitive to the type of reinforcement. During electrical (painful) reinforcement, noradrenergic mechanisms are activated, whereas during food reinforcement, brain norepinephrine levels decrease instead. A pharmacological deficit of this neurotransmitter causes amnesia, slows down learning, and hinders the retrieval of already formed memory traces.

Serotonergic and dopaminergic systems Dopamine performs a general modulatory function in memory mechanisms. Serotonin is responsible for memory consolidation (transition from short-term to long-term memory). According to E.A. Gromova, the serotonergic system is especially active during learning against the background of emotionally positive reinforcement.

Molecular cascade and memory stabilization

The formation of long-term memory requires structural consolidation. Monoaminergic systems trigger a complex molecular cascade inside cells:

1. First, intracellular postsynaptic processes are activated.
2. Second messengers—cyclic nucleotides (cAMP and cGMP)—enter the reaction.
3. Under their influence, metabolic pathways leading to the synthesis of specific protein molecules are activated.
4. The synthesized proteins are integrated into synaptic membranes, stabilizing the primary changes. This is how the memory trace is reliably anchored in brain structures.

Synaptic mechanisms and the Lynch-Baudry concept

At the core of any memory lies the engram—the physical trace of a memory, which is a zone of increased synaptic conductivity. Glutamic acid and gamma-aminobutyric acid (GABA) actively participate in this process.

The detailed molecular mechanism of engram formation is described by the G. Lynch and M. Baudry concept:

• Upon repeated neuron stimulation, the concentration of calcium ions ($Ca^{2+}$) in the postsynaptic membrane region increases sharply.
• Calcium activates a specific enzyme—calcium-dependent protein kinase.
• This enzyme cleaves one of the structural proteins of the postsynaptic membrane.
• As a result of the cleavage, glutamate receptors that were previously in an inactive state are "unmasked" (released).
• The total number of active receptors increases, leading to a sustained increase in synaptic conductivity.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Exact molecular mechanisms of GABA and glutamate participation in memory formation
• Microiontophoresis: the essence of the method and its application in studying cholinergic receptors
• Differences in the noradrenergic system's operation during food versus pain reinforcement
• Mechanisms of cAMP and cGMP participation in the synthesis of specific memory proteins

Other topics in the "Memory" section

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