Engrams: the traces that experiences leave in the brain

We explain what these brain "marks" are and their role in memory and learning.

We are involved in a traffic accident, when a red car crashes into our vehicle. This accident generates a series of injuries from which we end up recovering, but at the cost of great suffering and anxiety. The day comes when we take the car again, and we notice that in front of any red car, we shudder and get very nervous. The reason for this is logical to most of us. However, what is not so well known is what generates it at the cerebral level.

That is to say, we know that various neurons will be activated that will generate different effects, largely mediated by the limbic system. But how exactly do these neurons relate to each other in order to react concretely to situations similar to experiences we have already had? In this sense, there are neural circuits that are formed throughout development and life, and which, after being formed, remain more or less stable: we are talking about engrams.

Engrams: what are we talking about?

By engram we mean a stable neuronal structure generated by stimulation, whether external or internal, and which is linked to the activation of specific responses, whether unconscious or conscious. The engram is the group of neurons, or neuronal circuit, which is neuronal circuit, which is activated upon perception of certain information..

Another frequent term to refer to this type of structure is the neuronal loop. In summary, it could be understood as the Biological basis of a trace or scheme of functioning derived from experimentation, as the set of brain changes resulting from learning and what we memorize. It would be the process of formation of concrete neuronal connections that, when activated, reproduce subjective experience. when they are activated reproduce the subjective experience that generated the event that gave rise to them.

The engrams can be both sensory and motor, being in them the basic programming of how to perceive or act before the stimulation. Both can be related. Although the formation of engrams is unconscious, these structures generate and influence both conscious and unconscious processes. They can trigger the generation of thoughts, emotions, movements or activation of physiological mechanisms.

In our brain there are a great number of these structures, being the engrams generic neuronal structures that are involved in a great number of mental functions. involved in a large number of mental and physiological functions.. It is a system that generates the synaptic facilitation and connection between different neurons, generating a closed circuit that reacts to stimulation awakening in turn other engrams that react and generate different responses.

Formation and psychobiology

The formation of engrams occurs in response to the encoding of the experience and the neuronal activation that this generates. The repeated exposure to certain stimulation or to derivatives of it causes the consistent activation of specific neurons or nerve pathways. The information that activates them can come from many different sensory pathways or modalities.

At the cellular level, the axon of the presynaptic neuron generates the excitation of the postsynaptic neuron repeatedly, which eventually generates a change in both in such a way as to improve the efficiency of their intercommunication. It also allows more synapses to be established, reinforcing the circuit and connecting to other loops that generate a response to stimulation.It also allows more synapses to be established, reinforcing the circuit and connecting with other loops that generate a response to the stimulation.

At the neurotransmitter level, the communication of neurons that are part of an engram is mainly carried out by acetylcholine, although other hormones such as noradrenaline also have some effect.

However, it is necessary to take into account that in order for the engram to be fixed it is considered necessary that there is an activation of the limbic systemespecially those regions linked to motivation, due to the need for us to give importance to an event in order to generate automatisms.

Its role in memory

Engrams have an important role in allowing stable storage of information and recall of previous information: they are stable neuronal structures, which will be activated in a certain way and will continue to function in the same way unless changes are introduced or new synapses are created.

They are fundamental in allowing the storage of memory.They are therefore the biological basis on which is based, for example, the repetition of certain behaviors or ways of reacting to certain situations. Engrams make us sensitive to specific stimulations and make it easier for us to react to them in previously learned ways.

This, for example, causes that a person who has suffered some type of aggression or abuse has generated changes that make that before similar stimulations (for example the physical contact of someone of the sex of the attacker, although the person who is now approaching us is not attacking us and has no bad intentions) can react with fear or defensiveness.

We are not saying that all engrams correspond to negative or traumatic experiences, but also to those that generate very positive emotions. For example, a child ends up generating engrams that relate to the maternal or paternal figure with feelings of security and protection, which is why he or she may feel bad if they are not there or seek their closeness in case of discomfort.

Not only in memory

So far we have mainly talked about the engram as a brain circuit linked to learning and memory. as a brain circuit linked to learning and memory.. But the truth is that engrams are not limited to this sphere: if we think of engrams as brain circuits that are activated by information, aspects such as perception, motor skills (how to walk for example), knowledge (including theory of mind), language, experience and emotional expression are also determined (although modifications and changes can be introduced) by these structures.

Bibliographical references

• Cardinali, D.P. (1992). Manual of Neurophysiology. Ediciones Diaz de Santos, S.A. Madrid, Spain.
• González, J.L. (1987). Structure and function of the human mind. Psiquis, 346 (8).
• Lashley, K.S. (1950). In Search of the engram, Symp.Soc.Exp.Biol., 4: 454-482.
• Montserrat, J. (n.d.). Neural engrams and theory of mind. Universidad Autónoma de Madrid. Madrid, Spain.