Inserm, Science for Health

Understand the functioning of memory

Memory is the function that allows us to integrate, conserve and restore information to interact with our environment.It brings together know-how, knowledge, memories.It is essential for the reflection and projection of each in the future.It provides the basis of our identity.

Five interconnected systems

Memory consists of five interconnected systems, involving distinct neural networks:

We sometimes bring together all memories other than that of work under the generic name of long -term memory.Furthermore, we often distinguish explicit (episodic and semantic) memories from implicit (procedural and perceptual) memories.

La mémoire de travail

Working memory (or short -term memory) is the memory of the present.It makes it possible to manipulate and retain information during the completion of a task or an activity.

This memory is permanently requested: it is it which allows for example to retain a telephone number while noting it, or to retain the beginning of a sentence time to finish it.It uses a phonological loop (mental repetition), which retains the information heard, and/or a visuospatial notebook, which retains mental images.

It works like a buffer memory: the information they convey can be quickly erased, or stored in long -term memory through specific interactions between the working memory system and long -term memory.

7, the magic number

It is estimated that the number of figures, letters, or words that a person can immediately restore in the proposed order is equal to 7, more or less two (we speak of the verbal empan).It can be increased by grouping the data (a series of 8 -digit is easier to remember when grouped by 2 than when they are taken in isolation).In addition, a series of words is all the easier to remember as they are short or that they are close phonologically or semantically.

La mémoire sémantique

Semantic memory is that of language and knowledge on the world and on oneself, without reference to the conditions for acquiring this information.It is built and reorganized throughout our lives, with the learning and memorization of generic concepts (sense of words, knowing about objects), and individual concepts (knowing on places, people ...).

La mémoire épisodique

Episodic memory is that of personally experienced moments (autobiographical events), the one that allows us to situate ourselves in time and space and, thus, to project ourselves into the future.Indeed, telling a memory of your last vacation or projecting yourself in the next ones call on the same cerebral circuits.

Episodic memory is formed between the ages of 3 and 5 years.It is closely nested with semantic memory.Gradually, the precise details of these memories are lost while the features common to various experiences experienced their amalgam and gradually become knowledge drawn from their context.Thus, most episodic memories are transformed, in the long term, into general knowledge.

La mémoire procédurale

Procedural memory is the memory of automatisms.It allows you to drive, walk, cycle or play music without having to relearn each time.This memory is particularly requested among artists or athletes to acquire perfect procedures and achieve excellence.These processes are carried out implicitly, that is to say unconscious: the person cannot really explain how he proceeds, why he is in balance on his skis or descends without falling.The movements are without conscious control and the neural circuits are automated.

The constitution of procedural memory is progressive and sometimes complex, according to the type of learning to which the person is exposed.It is gradually consolidating itself, while forgetting the traces relating to the learning context (place, teacher, etc.).

La mémoire perceptive

Perceptual memory is based on our senses and most of the time operates without the individual.It allows you to retain images or noises without realizing it.It is she who allows a person to go home by habit, thanks to visual landmarks.This memory allows you to remember faces, voices, places.

With procedural memory, perceptual memory offers humans a capacity for cognitive economy, which allows them to engage in specific thoughts or activities while carrying out routine activities.

Memorization: brain organization….

There is no "" center of memory in the brain.The different memory systems involve distinct neural networks, distributed in different areas of the brain.Functional imagery (positron emission tomography, functional magnetic resonance imaging) today makes it possible to observe normal brain function involved in cognitive processes.

Thus, the role of the hippocampus and the frontal lobe seems particularly decisive in episodic memory, with a preponderant role of the left and right prefrontal cortex in its encoding and its recovery, respectively.Perceptual memory is recruiting networks in different cortical regions, near sensory areas.Semantic memory involves very extensive regions, and particularly the temporal and parietal lobes.Finally, procedural memory is recruiting subcortical neural networks and at the cerebellum.

The information storage phase requires repeated consolidation stages.The hippocampus seems to be an important element in the process.Finally, the restitution of a memory, whatever its seniority, would also be based on this brain structure, in interaction with different neocortical regions.However, it would be less requested when the recall comes from semantic memory rather than episodic memory.

... with synaptic plasticity

The memorization results from a modification of the connections between the neurons of a memory system: we speak of "synaptic plasticity".The different forms of memory work in interaction, depending on whether the situation requires information from semantic or episodic, implicit or explicit memory.Thus, a memory is reflected in the intervention of neurons from different brain areas and assembled in networks.These interneuronal connections are constantly evolving according to experiences and are responsible for the persistence of a long -term memory or not, depending on the case (importance of the event, environmental and emotional context, etc.).

Taken in isolation, the memory corresponds to a variation in electrical activity at the level of a specific circuit formed by several neurons interacting through synaptic connections (synapses being the points of contact between neurons).His training is based on the strengthening or creation of a temporary synaptic connection, stimulated through proteins produced and then transported within neurons, such as glutamate, NMDA or syntaxin which will itself modulate the release of glutamate.

The memory is then consolidated or not according to the presence of cellular mediators at the level of the neural network involved in the following hours.The regular and repeated activation of this network would strengthen or reduce these connections and, therefore, consolidate or forget this memory.Morphologically, this plasticity is associated with changes in shape and size of synapses, transformations of silent synapses into active synapses, the growth of new synapses.

The long -term maintenance of a memory is based on the modification of the kinetics of elimination or renewal of certain mediators.Phosphokinase Zêta (PKM Zêta) plays a preponderant role in this mechanism by promoting the persistence of the mechanisms involved in the stabilization and consolidation of memories.For this, it has two specific properties: it is not subject to any inhibition mechanism and it can be used.

During aging, the plasticity of the synapses decreases and the modifications of the connections are more ephemeral, which could explain increasing difficulties in retaining information.

The cognitive reserve, memory support

The ability to maintain memory and adaptation in the event of lesions seem variable from one individual to another.Indeed, it has been described that with equivalent brain lesions in imaging, not all would present the same cognitive alterations.These capacities would depend on the brain reserve, relating to the brain fabric, and the cognitive reserve, which is based on its functionality.

According to various studies, an increased brain volume, or a high number of neurons or synapses is associated with a later occurrence of dementia.With equivalent lesions, those with a larger brain reserve would have less severe disorders.This cerebral reserve would be under the influence of genetic and probably environmental parameters.

The cognitive reserve corresponds to the effectiveness of the neural networks involved in carrying out a task and that of the brain to mobilize or set up compensatory networks in the event of pathological lesions or physiological disturbances related to age.It also results in variability, from one subject to another, of the tolerance of identical brain lesions.Indeed, the available data suggest that the richness of interactions and the level of education are associated with a later occurrence of cognitive disorders or alzheimer or related dementia.Conversely, the evolution of cognitive decline in them would be faster once installed: it would be explained by the fact that the symptoms are identified at a stage where the lesions are more numerous and important.

The constitution of the cognitive reserve could depend:

Hygiene of life and memory

Experiences have shown that sleeping improves memorization, especially since the duration of sleep is long. Conversely, sleep deprivation (less than 4 or 5 hours per night) are associated with memory disorders and learning difficulties. In addition, electrically stimulating the brain (stimulation of 0.75 Hz) during the slow sleep phase (characterized by the recording of slow cortical waves with encephalogram) improves the memorization capacities of a list of words. Several hypotheses could explain this phenomenon: during sleep, the hippocampus is at rest, avoiding interference with other information at the time of the encoding of memory. It could also be that sleep exerts, ridding the memories of Their emotional component to retain only the information, thus facilitating encoding. To find out more, consult the sleep file.

Sleep is not the only lifestyle parameter that influences our memorization capacity: food (benefit from the Mediterranean regime), physical activity and social activities also play an important role.

Memory and emotions: from memory to pathology

It is shown that emotions can adjust the way information is recorded, emotion punctually reinforcing attention. Thus, a positive emotion can result in a punctual improvement in memory performance. It also appears that consolidation, and therefore the retention of information is favored by emotion: the recall of an emotional memory after a long interval is often more important than when this memory is neutral. Functional imagery shows that the recall of memories is proportional to their emotional intensity which can be observed by the activation of the amygdal, seat of emotions. Finally, the recovery of a memory is also improved by the presence of a positive emotion. In people with cognitive disorder, experiences show a protective effect of positive emotions on residual memory capacities. However, this mechanism exists only in the early stages of the disease. Then, the inability of the amygdal to fulfill its role makes this compensatory mechanism ineffective.

There is a pathological counterpart to this process: indeed, an overly intense emotion, especially traumatic, leads to a distortion of encoding.The state of post-traumatic stress (ATSP) of people victims or witnesses of a dramatic event is a standard illustration.The memory is memorized in the long term, with both an amnesia of certain aspects and hypermnesia of other details which leave the person haunted permanently by this event.It is accompanied by a glucocorticoid discharge (stress hormone), in the hippocampus at the time of the event.This deep distortion of the encoding of events, unlike a normal memory, makes the memory persistent over time without it losing its intensity or its specificity.The victim thus has the feeling of continuously reliving the traumatic scene, even years later.

In other situations also relating to a lively emotion (stress, aggression ...), certain subjects are more readily developing dissociative amnesia: a true adaptive defensive strategy, developed in an unconscious way, it is based on the forgetting of a partAutobiographical or semantic memories, as well as the event having triggered it.These memories can be reactivated, gradually or suddenly, after a awareness of the trigger.

On the therapeutic level, understanding the mechanisms of stability of memories and emotional influence offer the means to envisage the therapeutic management of certain pathologies: thus, the development of psychotherapeutic approaches based on the dissociation between memories andEmotions can reduce disability linked to diseases such as certain forms of anxiety or post-traumatic stress.

Memory and forgetfulness: from physiological to pathological

For the past twenty years, the growing prevalence of memory disorders such as Alzheimer's disease has made us forget a symptom.However, forgetting is also a physiological process, essential for the proper functioning of memory.

In fact, forgetting is necessary for the balance of the brain, allowing the latter to select the secondary information that can be eliminated so as not to saturate the neural circuits.Oblivion is a corollary of the quality of hierarchy and the organization of stored information.Thus, some people suffer from idiopathic hypermnesia, a pathology of abstraction and the generalization of the memory in which the forgetting of the details is abolished.These people encounter daily life difficulties linked to the inability to organize their memories according to their significance and their importance.

However, forgetting can also correspond to the involuntary disappearance of memories acquired by voluntary or implicit learning, while its coding has been carried out correctly.This phenomenon remains physiological as long as it is sporadic.It concerns episodic memory more often than semantic, procedural or sensory memory.It becomes pathological, and more readily takes the name of amnesia, when it concerns whole sections of semantic or episodic memory.

Multiple memory disorders

Certain situations lead to severe disabilities and lasting amnesia.The possible causes are:

In other cases, disorders are less severe and most often reversible.The possible causes are:

Memory disorders have different biological origins, such as a deficit in certain neuromediators or low connectivity between brain networks.

The manifestations of these disorders are extremely variable according to their origin and the brain locations of the pathological processes. Thus, patients with semantic dementia, in which words or information are forgotten, also lose ancient memories while they continue to memorize new episodic memories (memories "day by day"). These disorders are associated with an atrophy of temporal lobes. In other patients, including those suffering from Alzheimer's disease, disorders concern episodic memory: in them, the oldest memories are spared longer than the most recent. Other types of disabilities exist: those affecting the neurons involved in procedural memory can cause the loss of certain automation, as in people affected by Parkinson or Huntington's disease. Those affecting the neurons involved in the memory of work, can give difficulties in concentrating and making two spots at the same time.

There are also severe but transient memory disorders, such as idiopathic amnesiac ICTIS: most often occurring between 50 and 70 years, it is a sudden and massive amnesia during which the patient is unable to rememberWhat he just did, his episodic memory is annihilated.But his semantic memory is intact: he can answer vocabulary questions and evoke general knowledge.This amnesia often disappears after six to eight hours.

Research issues

Memory and its disorders give rise to numerous research which uses various expertise in a multidisciplinary framework: genetics, neurobiology, neuropsychology, electrophysiology, functional imaging, epidemiology, different medical disciplines (neurology, psychiatry, etc.), but also human sciencesand social.

My memory and that of others

Memory has long been considered individual and studied as such.This approach is now obsolete, or at least incomplete.The memory is indeed at the interface between personal identity and collective representations: it is constituted from the interactions between the person, the others and the environment.He cannot be detached from the social context in which he takes place.Interactions, but also social representations and stereotypes influence the functioning of our memory.

We are talking about social cognition: it allows, for example, to adapt its behavior according to the context in which we are, and this thanks to the memorization and the analysis of past experiences.Empathy also stems from this interindividual notion of memory: it notably uses information from episodic memory in order to allow a "travel of the mind" resulting in capacity to share the distress of the other.Also called "theory of the mind", this ability to put oneself in the place of someone and to imagine and interpret his thoughts calls upon our memories whose object we decent.On the medical level, the degeneration of neurons at frontotemporal level, found in certain dementia (Alzheimer and related), is characterized by a reduction in social cognition: the patient can present behavioral disorders or social dysfunctions.

Furthermore, on a broader level, there is also a collective or cultural memory, that which takes place around historical events (around their evocation or their commemoration) and contemporary mediatized events.It is a shared memory made up of the different representations of the event by all people.

This field of research is particularly innovative and brings together expertise in neuroscience and psychology of those in sociology, history, philosophy or ethics.In therapeutic terms, this transdisciplinarity can also bring an interest: the state of post-traumatic stress corresponds for example to hypermnesia of perceptions and emotions linked to the event, to an amnesia of contextual aspects, as well as to a disturbance ofAutobiographical memory.Following a traumatic event, an appropriate care of the associated emotional load could be all the more effective since the event in question is registered in the social framework, both family and professional.This would be all the more question in the context of an event inscribed in the collective memory.

Sonder la mémoire individuelle et collective des attentats

The November 13 program, led by researchers from Inserm and CNRS, associates various components of transdisciplinary research around the testimonies collected on the attacks of November 13, 2015. It seeks to assess how the traumatic memory of the attacks evolves in the Memoirs Individual and collective, how the two work in interaction and what are the vulnerability factors in the face of PTSD. On four occasions for ten years, testimonies and possible disorders (ATSP, invasive images, depression, etc.) of 1,000 volunteers will be analyzed according to their proximity to the attacks: this cohort brings together people exposed directly (survivors, witnesses, families) , indirectly (residents of the attacks of the attacks) as well as the Ile -de -France or non -Ile -de -France residents. These data will be collected parallel to an analysis of the French opinion on the subject, as well as an analysis of the discourse and textometry of television or radio information linked to these events, in order to identify its interactions.

To find out more about the progress of this research project: program 13-November-stage point 5 years after the start of the project (press release of 10/11/21)

Memory in the future

Depending on the context, our own aspirations, our projects, we have an ability to develop plausible scenarios for the future, made up of thoughts, images and actions.These can only take shape on the basis of representations of the past.The memory of the future therefore uses our episodic and semantic memory, contrary to popular belief or the usual conceptions of memory, traditionally associated with the past.Thus, imaging makes it possible to verify that the evocation of an autobiographical memory or the imagination of a future scenario involve brain regions very close to each other.Furthermore, studies show that amnesiacs cannot project themselves into the future.

The ability to fulfill a task on a specific date or day also enters the memory of the future: it is then called more readily prospective memory, articulated around different components depending on the nature of the tasks to be performed: "Prospective memoryclean "for punctual actions (post a letter, go to an appointment ...)," usual prospective memory "for all routine tasks," monitoring "for the attention paid to the end of a task while aAnother is underway (remember to stop the oven at the end of cooking, for example).

This notion of memory of the future can have therapeutic applications.Thus, "therapies oriented towards the future" have been developed and tested with patients with major depression or schizophrenia: carried out through several sessions spread over a few weeks, they consist in raising awareness of the importance of mental projections inThe future, the way in which these can be improved by fighting against personal resistance mechanisms, then, gradually to offer them mindfulness activities and, finally, to work on the evocation of their own values, their objectives,and the means to get there.The first studies show that this approach can be more effective than conventional cognitive behavioral therapies.

External memories

It seems clear today that our internal memory and our projection capacities are influenced by external memory: collective memory supports (books, films, etc.) are a useful element for modeling our memory of the future.The multiplication of information storage of information storage in our daily lives is however described as modifying the organization and power of our memory, which we therefore solicit less.This balance between internal and external memory is a major issue for the future.

On the therapeutic level, external storage supports are today tested in the form of brain implants in the management of amnesiac patients.More futuristic, the idea of artificial memory transplant is also the subject of current developments.

Modify memory thanks to optogenetics

In addition to functional imagery, which is today part of the essential modes of exploration of the memory organization, other approaches are more recent and in full evolution.This is particularly the case with optogenetics, which is a technique combining genetics and optics: it consists in genetically modifying cells in order to make them sensitive to light and, thanks to the latter, to modulate its operation.Thus, optogenetics makes it possible to activate or inhibit specific groups of neurons in the brain tissue and to assess its impact.

It also makes it possible to develop methods of manipulation of memory (implantations of false memories, experimental oblivion, etc.).These works make it possible to envisage interesting therapeutic approaches in the management of certain psychiatric disorders.

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