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Ar.1: How to know everything about memory in 3 questions/answers

CHAPTER I: Memory and Learning

Article 1: How to know everything about memory in 3 questions/answers

[Welcome to the “Brain & IA” series: a series that compares neuroscience with artificial intelligence! The series will deal with different topics embodied through different chapters. Each chapter is composed of several articles. Each article can be read independently.]

Here you are in the first article ("How to know everything about memory in 3 questions/answers") of the first chapter of the series "Memory and Learning".

By reading the first article of this chapter, you will be able to tackle the memory functioning in the brain, but also to establish better strategies for learning. This article takes the form of question-and-answer.

What is memory in neuroscience?

We know that we have between 80 and 100 billion neurons in our brain. However, it is still impossible to know the maximal capacity of the human memory. Fortunately, the understanding of memory and learning in neuroscience is advanced.

First of all, we do not have one memory but several memories. These memories are distributed in two main categories: short-term memory (about seconds or minutes) and long-term memory (about days or years) (see Image 1). It is important to remember that the main goal of the memory is to be used in the future. In other words, memory is a projection of the past that we can use later (ex: use our knowledge or be able to cycle again).

Image1: Memories in neuroscience.

Short-term memory is made up of sensory memory and working memory. As its name suggests, sensory memory relates to our senses while working memory allows us to temporarily store information until we need it. For example, a phone number will be stored in the working memory until we dial it. Then, it will be immediately forgotten. We are able to retain 5 +/- 2 items in the storage space of this working memory: this is called the memory span.

Declarative memory and non-declarative memory compose long-term memory. The first one is “conscious” and is relative to facts that can be explicitly described, while the second one is “unconscious” and includes learning that is implicit or that cannot be described.

Episodic memory and semantic memory form the declarative memory. Episodic memory relates to our personal memories (for example, the exquisite meal I ate last week). On the other hand, semantic memory concerns generic facts about the world (for example, knowing “the earth is round”). The facts of episodic memory are generally linked to a time index unlike the facts of semantic memory. Indeed, we are able to evoke a childhood memory by specifying a date (age range, year), while we are unable to specify the date on which we learned that Paris is the capital of France.

Finally, non-declarative - or unconscious - memory is generally described by procedural memory or motor memory. Thanks to this memory, you will be able to cycle even after 20 years of training break.

How do we learn and how do we promote good learning?

Memory is necessary for learning. To create a new memory, we make bridges between the different memories.

Learning begins with the capture of a stimulus through our sensory organs. The information of this stimulus is stored in our sensory memory thanks to our perception. Then, this information is distributed in the working memory by our attention.

If we repeat this information, it will be encoded and consolidated in the long-term memory to create a new memory. If we want to use this information again, we will retrieve it in the working memory (see Image 2).

But let's not forget one thing ...

“Learn is forget” - JP Changeux

Forgetting is necessary! Synapses that are not used are recycled to make room for new memories.

Image 2: The learning process.

Thus, intelligence is also the ability to extract information, sort, and formalize them.

Furthermore, to promote good learning, sleep is essential: it is during the sleep phase that we repeat our past events during the day. This key phase is more important in children who have a repetition cycle almost 3 times faster than adults.

To better learn, it is also possible to establish a strategy based on the learning frequency. The optimal frequency of learning corresponds to 20 to 30% of the total time during which we want to remember the information. For example, if we would like to retain information for 1 month, we need to revise it regularly for a few days.

Are there other factors that negatively or positively influence learning?

Dopamine and stress (mainly managed by cortisol) are powerful modulators. Dopamine plays a critical role in motivation and curiosity, factors that are identified as pillars of learning (1). Stress is also a strong modulator in learning or in retrieving our memories.

The “time-space convergence” is often mentioned: it reflects the fact that stress has different impacts (negative or positive) depending on when it was felt. Stress during learning tends to improve the creation of new memories (2). It may strengthen the synapses associated with this memory by activating the production of neuronal adhesion molecules (NCAM) (see Image 3). And, the role of these molecules is to connect two neurons and stabilize a synapse. Furthermore, if we prevent the activation of NCAMs in mice by genetic manipulation, learning deficits and reduced memory capacities appear (3).

However, stress interferes also with memory recovery. The loss of memories during school exams is a concrete example. In addition, stress would interfere with the updating of new memories and promote rigid and habitual behavior instead of “flexible” and “cognitive” learning (2).

In short, the stress associated with the time of learning - if it is not chronic - could enhance the creation of new memories. The emotions associated with a situation tend to create a more robust consolidation. However, being stressed after the learning phase would impair memory access.

Image 3: Adhesion molecules in synapses (6)

[translation: Neurone présynaptique: presynaptic neuron; Influx nerveux: nerve impulse; Neurotransmetteur: neurotransmitter; Récepteur: receptor; Molécule d’adhérence: adhesion molecule; Neurone postsynaptique: postsynaptic neuron.]

Thus, to better learn, we need to:

  1. Sleep well

  2. Regularly distance learning (repetitions)

  3. Foster curiosity and motivation

  4. Relax before the fateful moment (exam, job interview, etc.)!

How does the learning process take place in our brain?

Good learning is equivalent to good synaptic plasticity, namely the good capacity to change our brain. This synaptic plasticity takes place thanks to a molecular process known as "Long Term Potentiation" (LTP). LTP was discovered in 1966 in a brain structure responsible for creating new memories: the hippocampus. Today we know that LTP is a process that is not isolated in the hippocampus.

LTP corresponds to a lasting reinforcement of our synapses (i.e. synaptic strength) in order to encode new memories. The more we perform a task or the more we use memory, the more we appeal to synapses relating to that task/memory. The synaptic strength is modulated according to the repetition of these stimuli. For example, if we no longer use a phone number, it will be forgotten over time because the synaptic strength associated with that memory will decrease over time.

But how does LTP take shape in our brain? First of all, remember that the passage of information in the brain is performed thanks to the circulation of a nerve impulse from neuron A to neuron B. LTP is an amplitude increase of this postsynaptic response (neuron B) after a high-frequency stimulation of the presynaptic neuron (neuron A). More simply, LTP describes the mechanism by which neuron B produces a higher response after highly stimulating neuron A. This answer of the neuron B can be lasting.

This change in response amplitude can cause a structural modification of the synapse: new receptors (molecules that receive the message from neuron A to neuron B) on the postsynaptic face can appear, new synapses can be born or pre- or postsynaptic areas can widen (4).

Image 4: The long-term potentiation causes structural changes in concerned neurons (here, the creation of new dendritic spines) (5).

But where are our memories located in our brain? The creation of new memories takes place in the hippocampus - a structure under the cortex that is associated with memory. Once memories are created, it is assumed that memories are moved and stored in the concerned cortical region. For example, the memory of an image will be stored in the visual cortex.


How did we discover that the hippocampus is responsible for creating new memories?

We owe this discovery thanks to the patient “HM” (Mr. Henry Gustav Molaison): a patient who suffered from epileptic seizures. In 1953, at the age of 27, he underwent surgical removal of the regions responsible for his epileptic seizures. The hippocampus was largely targeted so this region was almost entirely pulled out. From that moment on, patient HM lived with anterograde amnesia: he was unable to store new memories in long-term memory but he kept intact short-term memory. However, some facts were still strange: he remembered that he had "memory problems" or that "a famous person named Kennedy was murdered". In addition, his amnesia particularly reached explicit/declarative memory while part of his implicit memory responsible for motor skills remained intact (“mirror-drawing” tasks) (5). This discovery was exceptional and allowed, to the detriment of the patient HM, to locate the center of the creation of new memories as the hippocampus.

This is the end of this first article. See you soon for the second article of the chapter "Memory and Learning"!


  1. Berke, J.D. What does dopamine mean?.Nat Neurosci 21, 787–793 (2018).

  2. Vogel, S., Schwabe, L. Learning and memory under stress: implications for the classroom. npj Science Learn1, 16011 (2016).

  3. R. Bisaz et al., Learning under stress : a role for the neural cell adhesion molecule NCAM, in Neurobiol. of Learning and Memory, vol. 91(4), pp. 333-342, 2009.

  4. C. Bromer et al., Long-term potentiation expands information content of hippocampal dentate gyrus synapses, PNAS USA, 6 mars 2018.


  6. Neurosciences, D.Purves et al., De Boeck, 2013.

  7. L'incroyable histoire de l'intelligence,S. Dehaene, Y. Le Cun, J. Girardon, Robert Laffont, 2018.

  8. Cerveau&Psycho - n° 48 novembre - décembre 2011

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