Hebb’s so-called law, Proposed by neuropsychologist Donald Hebb, states that synaptic connections are strengthened when two or more neurons are activated contiguously in time and space. When presynaptic cell firing is associated with postsynaptic activity, structural changes occur that promote the emergence of neural assemblages or networks.
In this article, we will analyze the main approaches of this theory, which had a determining influence on neuropsychology: among others, Hebb’s rule is considered to have inspired the concept of long-term potentiation and the models of neural networks that explain learning and memory.
Role of neuronal plasticity in learning
From the point of view of neuroscience, 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.
Over the past decades, the hypothesis that our brains store information in neural networks has gained great popularity and strong scientific support. The structure of the nervous system and the relationships between its elements constitute the information we process; memory, in turn, is the activation of these networks.
The origin of this type of approach goes directly to a specific hypothesis: Donald Hebb’s cell assembly theory. The study of neural networks, which constitutes a central framework of current cognitive neurosciences, has been developed around the basic principles proposed by this author.
Hebb’s law (or cell assembly theory)
In 1949, psychologist Donald Hebb published the book “The Organization of Behavior”, in which he developed a pioneering theory of the neural basis of learning. While Hebb’s proposition is called “cell assembly theory,” it is generally referred to by the term by which its basic principle is known: Hebb’s law.
Hebb’s rule states that if two neurons are active at around the same time, their connections are strengthened. Specifically, Hebb said that if the axon of neuron A is close enough to cell B and repeatedly helps trigger it, certain structural or metabolic changes will increase the efficiency of such a synapse.
More precisely, this would cause the appearance of terminal buds, or the enlargement of 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 give rise to engrams or cell assemblies – nowadays “neural networks”.
This way the stronger it is the contingency between neuronal activation and a certain type of stimulationThe greater the likelihood that the affected neural networks will trigger impulses when the stimulus recurs. It also explains why the practice or examination makes it difficult to weaken synapses (such as forgetting).
For this to happen, Hebb proposed, the first neuron must be activated immediately before the second; if the neural trait occurs in both cells at the same time, however, no causation is given to the synapse, so the connection would not be strengthened in the same way.
However, this law only explains the strengthening of associations, not their formation. like that, learning is based on the consolidation of pre-existing synapses, Determined primarily by biological and genetic variables. According to Hebb, each neural circuit can be directly linked to a learned activity.
Influence of this neuropsychological model
Hebb’s proposal had a strong impact on neuropsychology, becoming the heart of many approaches developed in recent decades, and remains today a very important reference in this field.
In the early 1970s, the existence of a very relevant learning mechanism was discovered: long-term empowerment, which involves consolidating memories through repeated experience. Thus, short-term memory is regulated by structural changes (gene expression, protein synthesis and changes in synapses).
The validation of this model supported Hebb’s fundamental thesis, determining the specific biological bases that explain his law. Today, we also know with certainty that long-term potentiation is limited exclusively to neurons that are active at the same time, and that if multiple synapses converge to the same neuron, they are further enhanced.
One of the latest apps from Hebb’s rule concerns mirror neurons, Which are activated both when performing a behavior and when we see another living being doing the same and are understood as the basis of empathy and theory of mind. The relevant synapses were shown to be strengthened according to Hebb’s law.