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Hebb's Law: the neuropsychological basis of learning

Hebb's Law: the neuropsychological basis of learning

May 23, 2024

The so-called Hebb's law , proposed by the neuropsychologist Donald Hebb, states that synaptic connections are strengthened when two or more neurons are activated contiguously in time and space. By associating the firing of the presynaptic cell with the activity of the postsynaptic, structural changes take place that favor the appearance of assemblies or neural networks.

In this article we will analyze the main approaches of this theory, which had a seminal influence on neuropsychology: among other aspects, it is considered that Hebb's rule inspired the concept of long-term empowerment and the models of neural networks that explain learning and the memory.

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Role of neuronal plasticity in learning

From the neuroscience point of view, the biological basis of learning lies in neuronal plasticity . This concept refers to the ability of the nervous system to modify the nature and strength of synapses, that is, the connections between neurons that allow the transmission of electrochemical impulses.

In the last decades, the hypothesis that our brain stores information in neural networks has acquired great popularity and strong scientific support. The structure of the nervous system and the relationships between its elements constitute the information we process; the memory, on the other hand, consists in the activation of these networks.

The origin of this type of approach goes back directly to a specific hypothesis: the cell assembly theory of Donald Hebb . The study of neural networks, which constitutes a framework of nuclear work in current cognitive neuroscience, has been developed around the basic principles proposed by this author.

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The law of Hebb (or Theory of the cellular assembly)

In 1949 the psychologist Donald Hebb published the book "The organization of behavior", where he developed a pioneering theory on the neural bases of learning. Although Hebb's proposal is called "Theory of the Cellular Assembly", it is usually referred to through the term by which its basic principle is known: Hebb's law.

Hebb's rule states that if two neurons are active at approximately the same time their connections are strengthened . Specifically, Hebb said that if the axon of neuron A is close enough to the B cell and repeatedly contributes to firing it, certain structural or metabolic changes will increase the effectiveness of such a synapse.

Specifically, this would cause the appearance of terminal buttons, or the enlargement of other existing ones, in the axon of the presynaptic neuron; these would be in direct contact with the soma of the postsynaptic cell. The physical and functional association between different neurons would lead to engrams or cell assemblies -now "neural networks".

In this way, the stronger it is the contingency between neuronal activation and a certain type of stimulation the greater the probability that the relevant neural networks will trigger impulses when the stimulus occurs again. This also explains why the practice or review makes it difficult for synapses to weaken (as in oblivion).

For this to happen, Hebb proposed, it is necessary that the first neuron be activated immediately before the second; if the neural firing occurs at the same time in both cells, however, there is no causality in the synapse, so the connection would not be strengthened in the same way.

However, this law explains only the strengthening of associations, and not their formation. A) Yes, learning is based on the consolidation of pre-existing synapses , determined fundamentally by variables of biological and genetic type. According to Hebb, each neuronal circuit can be directly related to a learned activity.

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Influence of this neuropsychological model

Hebb's proposal had a strong impact on neuropsychology, becoming the core of many approaches developed in the subsequent decades, and remains a very important reference in this field today.

At the beginning of the 70s, the existence of a very relevant mechanism for learning was discovered: long-term empowerment, which consists of the consolidation of memories through repeated experience.Thus, short-term memory is based on structural changes (gene expression, protein synthesis and changes in synapses).

The validation of this model gave support to the fundamental thesis of Hebb, determining the concrete biological bases that explain its law. Nowadays we also know with certainty that the long-term potentiation is limited exclusively to neurons that are active at the same time, and that if several synapses converge in the same neuron these are further strengthened.

One of the most recent applications of Hebb's rule is related to mirror neurons , which are activated both when we execute a behavior and when we see another living being doing the same and are understood as the basis of empathy and the theory of the mind. It has been discovered that the relevant synapses are strengthened following Hebb's law.

Hebb's Three Postulates: from Brain to Soma (May 2024).

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