Neuronal Plasticity: Characteristics And Types

The term neuronal plasticity refers to the ability of the nervous system to change, both functionally and structurally, in response to the passage of time or injuries. Colloquially, plasticity is known as the property of a material to be physically malleable.

In a more scientific way, we can say that neuroplasticity is the ‘capacity of the nervous system to respond to intrinsic or extrinsic stimuli by reorganizing its structure, connections and functioning’ (1).

Thus, plasticity is a key concept in neuronal development and in the normal functioning of the nervous system. It is also a response to the changing environment, aging and the pathologies we can contract.

Thus, neuronal plasticity is necessary both for neuronal networks to acquire new functional properties and for them to continue producing sufficient brain connections.

The brain is, by necessity, a plastic structure. This has been demonstrated by several scientific researches.

Furthermore, we know that plasticity is present at various organizational levels of the nervous system. We can speak of nervous tissue plasticity, neuronal or glial plasticity, synaptic plasticity, etc.

How do neural networks work?

Neuronal plasticity occurs especially in response to physiological demands, changes in neural activity or damage to nervous tissue.

Furthermore, plasticity participates in the formation of the neural network during the development and acquisition of new motor behaviors or the learning that we accumulate during life. There are many biological processes involved in plasticity:

• Neurogenesis.
• Cell migration.
• Changes in neuronal excitability.
• Neurotransmission.
• The generation of new connections.
• Modification of existing connections.

Structural and functional neuronal plasticity

The plasticity of transmission efficiency between neurons may depend on adaptive changes in presynaptic, extracellular or postsynaptic molecules.

This means that plasticity can occur without modification of the number, location, distribution, density or total area of ​​synapses.

Long-term early potentiation and changes in electronic properties due to geometrical changes in dendrites are clear examples of this type of plasticity.

On the other hand, changes in circuit connectivity that involve synapse formation, elimination or expansion, such as long-term delayed potentiation, are encompassed in “structural or architectural plasticity”.

Hebbian neuronal plasticity and homeostatic plasticity

Transmission efficiency plasticity and structural plasticity can be classified as Hebbian plasticity and homeostatic plasticity, respectively (2).

Hebbian plasticity implies a change in synaptic strength, either increasing or decreasing according to the level of neuronal activity, on a time scale of seconds or minutes after the onset of stimulation.

Long-term early potentiation is a typical example of Hebbian plasticity. Initially, a tetanic stimulus drives coincident prior and postsynaptic activation, which induces increased synaptic efficacy.

This increase will improve potentiation. Thus, Hebbian plasticity produces a positive feedback loop.

In turn, homeostatic processes are slower, taking hours and even days. Thus, they may include changes in ion channel density, transmitter release, or postsynaptic receiver sensitivity.

In contrast to the Hebbian plasticity, the plasticity homeostatic constitutes a negative feedback circuit. Homeostatic dynamics decrease connectivity in response to high neuronal activity and increase connectivity when activity decreases.

It was proposed that the homeostatic plasticity and hebbianas have different roles in terms of functions neuronal network. Hebbian plasticity is involved in the changes that occur throughout life, the storage capacity and the robustness of memory.

Homeostatic plasticity self-organizes neural network connectivity to avoid network instability.

Furthermore, this type of plasticity implies synaptic and extra-synaptic mechanisms, such as the regulation of neuronal excitability, the regulation of synapse formation and the stabilization of the total synaptic strength and dendritic arborization.

Neuronal plasticity is a process that can be observed during the development of the nervous system. It appears as an essential attribute that gives the brain the ability to modify its structure and functioning in response to changes in neuronal activity.

It is also responsible for acquiring new abilities as substrates for learning and memory or the recovery of functionality after an injury.

In short, it is a process that allows the brain to remain flexible to provide a better adaptation to environmental conditions.