How does the brain memorize new information?

Diligent students will sometimes give up playing in the yard and stay in class during recess to repeat the material taught. Now it turns out that the amygdala (“almond” in Greek) in our minds is also prone to diligence: Weizmann Institute scientists have shown that the nerve cells in the amygdala, which are involved in emotional processes of learning and memory, “repeat the learned material” even during breaks between lessons and lessons. These findings, recently published in the scientific journal Nature Neuroscience, shed light on brain learning mechanisms and may be relevant in situations where these mechanisms have been disrupted, such as anxiety disorders and post-traumatic disorders.

The amygdala is an almond-like brain structure that is located in the deep lobe of many mammals, including humans, and is involved in associative learning processes where

In the brain, there is a connection between a particular sensory input, such as sound or visual input, to positive or negative experiences. This type of learning is also referred to as “classical conditioning” or “Pavlovian response,” according to Russian scientist Ivan Petrovich Pavlov, who first demonstrated it in dogs: it caused dogs to drool in response to a neutral stimulus (ringing a bell) by ringing the ring For serving food. These findings were breakthroughs in behavioral research – and this work even earned him a Nobel Prize in Physiology or Medicine in 1904. Nevertheless, the question of what exactly is going on in our brain while learning remains largely open-ended.

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Prof. Ronnie Paz and research student Tamar Reitish-Stolaro of the Department of Neurobiology at the Weizmann Institute of Science tried to answer this question. They made a distinction between a pleasant and appetizing scent (banana or melon scent) and another sound of disgust and repulsion (propanoic acid that resembles stinky socks). Unlike Pavlov, the researchers did not only settle for the behavioral aspects of learning, and recorded the activity of the nerve cells at various points in the brain in general and the amygdala in particular.

From the analysis of the activity of the recorded nerve cells, several findings emerged: First, the researchers identified different activity patterns in amygdala nerve cells that returned in a certain order in time and space (for example, activation of neuron 1, followed by neuron 3 and finally neuron 2 – and repeat). These patterns of activity differed between positive conditioning (pleasant smells) and negative conditioning (repulsive smells), and were repeated not only during learning but also in the relatively long breaks between repetitions in learning.

The researchers concluded that these patterns of activity represent a coding mechanism for the new information (the affinity between sound and odor) and that repeating these patterns long after the stimuli ended, probably constitutes a “replay” mechanism that assists in the learning of the material and the formation of new emotional memory. Interestingly, as learning progressed and the connection between sound and smell was internalized – the number of repetitions of the activity pattern in nerve cells diminished, probably because learning was already assimilated and no further repetition was required.

Our emotions play a major role in learning and memory, and even allow us to survive in a changing environment through the conditions that help us to separate dangerous and safe stimuli from unpleasant and pleasant stimuli. However, this process can go awry in people with anxiety or post-traumatic stress disorder (PTSD), preventing them from distinguishing between dangerous and safe situations. In post-traumatic situations, a strong negative reaction, such as paralyzing fear, may arise as a result of a seemingly neutral stimulus (some noise, for example), only because in the past this stimulus preceded a traumatic event (e.g., squeaking of brakes prior to a life-threatening accident).

If repetitions of the material being taught do contribute to the learning process – the question arises if we interfere with the learning process after a traumatic event, can we prevent it from assimilating the negative condition or reducing its intensity – and thus also affect the intensity of the post-traumatic disorder? This therapeutic option has previously been raised in behavioral studies. Accurate characterization of the brain activity that reflects the repetition of negative conditioning may interfere with the trauma learning and assimilation process through medication or more surgical means – a brain stimulus that will prevent and repeat the negative event only.

For the full study:
https://www.nature.com/articles/s41593-019-0542-9