Memory is the essential brain function that allows us to develop a sense of self, to store memories, to reason, to understand, and of course to learn. We speak about it in the singular form, but it would be more correct to evoke it in the plural one. We understand now that it is composed of different systems which, although in constant interrelationships, are distinct and autonomous due to the nature of the information they store and the brain networks they use. Here is an overview of 8 aspects of our fascinating memory!
We all know the concepts of short and long-term memory, which cognitive psychology has long presented to us as our two great types of temporal memory. Over time, our knowledge of these has been refined, and we now comprehend a little more about their functioning, particularly through neuroscience (see Education Through the Lens of Neuroscience and The Fascinating Brain: 5 Amazing Facts). Let’s go back to these two basic models.
Sometimes called “working memory” (see point 4), short-term memory is used to temporarily store and retrieve – within less than a minute – the information being processed. It allows us to remember, for example, a name, a number or a list of elements.
Long-term memory can hold an unlimited amount of information over a period of a few hours to a lifetime. It encompasses the memory of recent events, still in processing state, as well as that of consolidated memories, which may, it should be pointed out, also be forgotten. Long-term memory is based on three major chronological processes:
- Encoding: This is the processing of the information coming from our senses, getting it ready to be stored in the memory.
- Storage (consolidation): This corresponds to the conservation of the information learned after being sufficiently repeated by the brain.
- Recall: This is a process that retrieves information from memory at the appropriate time; recall may be conscious or not, spontaneous (free) or facilitated (or “indexed,” facilitated by clues).
It can also be described as explicit (declarative), when it refers to memories that can be named, or implicit (non-declarative), when these memories do not verbalize and when their recall is automatically done – know how to ride a bike, for example. Finally, long-term memory is subdivided into several sub-types of memories (see points 5 to 8).
Here are 4 factors that can influence the functioning of memory:
- The degree of attention, alertness, awareness, and concentration.
- Interest, motivation, need or necessity.
- The emotional state and the emotional value assigned to the content to be memorized.
- The environment in which the memorization takes place (the place, the lighting, the noises, the smells, etc.), which records at the same time the data to be memorized.
First memory types
The sensory (or perceptual) memory: the one that filters
The sensory memory is, in a way, the first step in the processing of the information ready to be memorized: it is a filter through which all these stimuli pass from outside through our senses (sight, hearing, touch, smell, and taste).
To avoid being overwhelmed, this memory – which does not require our attention! – must make its selections and empty itself super fast. To give you an idea, from the sense of sight alone, our brain receives each second the equivalent of 1 Mb of information, which corresponds to reading an entire encyclopedia in a minute. The information retention time in sensory memory ranges from a few hundred milliseconds to one or two seconds. Without going into details, let us mention that the process that starts here is called “sensory transduction”: the sensory receptors transform the stimuli energy – chemical or physical, according to the type of receptor appropriate to each sense – into electrical signals (nerve impulses). At this stage, we do not yet speak of the memory of the senses as described by Marcel Proust (see the box The Little Madeleines or the memory of the senses) which requires a more advanced level of integration of information.
Information, in the form of electrical signals, follows different pathways to activate certain regions of the brain in order to be interpreted accordingly. The information deemed relevant is then encoded – processed to be stored – then transmitted to the short-term memory, a more stable memory, from where eventually it will pass into the long-term memory. Since each sense has its own system, its own circuit, each linked to a specific area of the cerebral cortex, we can speak of visual, auditory, olfactory, taste and tactile memories.
The sensory memory is not circumscribed to a single region of the brain but interconnected to other ones, participating in its proper functioning. By also recording emotions and sensations related to perceived sensory information, this memory not only recognizes our environment but also helps us to make sense of future events.
The working memory: the one that juggles with the immediate
The working memory is an updated concept of short-term memory. We understand now, thanks to neuroscience, that “short-term” memory does not only temporarily retain new information before it ends up in long-term memory, but it is also responsible for treating and manipulating it in processes such as reasoning, comprehension, and learning.
This so-called “immediate” memory includes several independent systems that allow the simultaneous execution of various tasks and involves a dialogue between three areas of the brain: the prefrontal cortex, the frontal ocular fields, and the lateral intraparietal zone. We can consciously memorize only 4 or 5 things at the same time. Recently, researchers have discovered that when working memory is overloaded, the exchanges between the three brain regions involved are then bypassed.
Long-term memory types
The procedural (or motor) memory: the one that has good reflexes
Procedural memory is an implicit (non-declarative) memory that allows us to perform ordinary tasks without having to think about them, as in eating, lacing shoes, riding a bike, and so on. It is the memory of motor skills and know-how. Since it is made of sensorimotor automatisms very well assimilated, this memory is called “unconscious.”
Episodic memory: one that has lived
Episodic memory allows one to recall memories lived personally in a given context – in such a place, at such a time, with such person, etc. – with its perceptive-sensory details (emotions, perceptions, smells, etc.). It is particularly distinguished from other types of memories by the fact that the individual sees himself as the actor who lived the events. This memory capability, which would be the most complex we possess, also includes the ability to make connections in time and space between various experienced events.
The quality of the encoding of memories by the episodic memory is also greatly influenced by the intensity of the emotions felt during the event. This type of memory is the one that is most affected by amnesic disorders.
Semantic memory: the one we have on the tip of the tongue
Memory of references, it stores and classifies the general knowledge of oneself – we speak then of “semantic personal memory” – and on the world which surrounds us: from the meaning of the words to the facts of encyclopedic type, by way of the rules and concepts that allow us to represent the world “in our head”. Unlike episodic memory, it is independent of the spatiotemporal context in which memories are acquired.
Autobiographical memory: the one that builds our identity
Autobiographical memory has long been confused with episodic memory. Although there is a link between the two and their interrelationship needs to be further clarified, the concept of autobiographical memory is much broader than that of episodic memory. In fact, it is a “hybrid” model that includes both a semantic and episodic component.
This memory, therefore, records general information about itself, without reference to a given context – our marital status, the names of our relatives, etc. – and unique memories distinctive to oneself – lived events located in time and space accompanied by their perceptive-sensory details. Over time, the construction of our sense of identity and continuity is primarily the result of this autobiographical memory.
Little madeleines or sensory memory
“(My mother) sent out for one of those short, plump little cakes called ‘little madeleines,’ which look as though they had been molded in the fluted scallop of a pilgrim’s shell. And soon, mechanically, weary after a dull day with the prospect of a depressing morrow, I raised to my lips a spoonful of the tea in which I had soaked a morsel of the cake. No sooner had the warm liquid, and the crumbs with it touched my palate, a shudder ran through my whole body, and I stopped, intent upon the extraordinary changes that were taking place. An exquisite pleasure had invaded my senses […].”
“And suddenly the memory returns. The taste was that of the little crumb of madeleine which on Sunday mornings at Combray […] my aunt Léonie used to give me, dipping it first in her own cup of real or of lime-flower tea.”
“But when from a long-distant past nothing subsists, after the people are dead, after the things are broken and scattered, still, alone, more fragile, but with more vitality, more unsubstantial, more persistent, more faithful, the smell and taste of things remain poised a long time, like souls, ready to remind us, waiting and hoping for their moment, amid the ruins of all the rest; and bear unfaltering, in the tiny and almost impalpable drop of their essence, the vast structure of recollection.”
Excerpt from: Marcel Proust, Remembrance of Things Past, Volume 1: Swann’s Way & Within a Budding Grove, 1913.
In Search of Lost Time
From Proust’s intuitions triggered by his Little Madeleines to the latest neuroscientific discoveries, going through the advancements in psychology, we have many pieces that help us recompose the puzzle of our memory … at least in part. Might be because it is still careful not to reveal all its mysteries. Moreover, if we ever manage to decipher all the codes, it’s a safe bet to say that this fabulous machine, which allows us nothing less than to have been, to be and become, will never cease to fascinate us.
To better memorize: breathe through the nose!
The way we breathe and the breathing phase (inspiration or expiration) have an impact on our memory. These are the astonishing findings of an American study published in 2016.
Olfactory oscillation was already known, a phenomenon that causes the olfactory system’s neurons to activate when the air enters the nose through the receptors at the end of the nasal hair. It was also known that there were four types of olfactory oscillations, some associated with learning and memory.
What the 2016 study has brought to light is the fact that the information is better stored if, at the moment when one takes knowledge of the information to memorize, one inspires by the nose. The expiration by the nose as well as breathing by the mouth (inspiration and expiration) do not have the same effect since it is the entry of air through the nostrils which allows the olfactory oscillations.
Memories transmitted by genes
Your DNA may well contain the memory of your ancestors, and it is not a figure of speech! This is suggested by experiments conducted on mice at Emory University whose results were published in 2013 in the journal Nature Neuroscience. As part of this work, the mice were trained to develop the fear of a smell similar to that of cherry flowers; training in which researchers noticed changes in the spermatozoa of rodents – part of the DNA that plays a role in the sensitivity of the smell to cherry flowers had become more active.
The mice were then allowed to mate. Their offspring, first and second generations, showed a noticeable sensitivity to this odor, encouraging them to avoid it, even though they had never been exposed to any traumatic experience related to it. The researchers, who have also observed changes in the brain structure of small animals, have concluded that “the experiences of a parent, even before conception, strongly influence the structure and function of subsequent generations.” In scientific jargon, we speak of “transgenerational epigenetic inheritance.”
The hippocampus: fundamental structure of memory and learning
We cannot talk about memory without mentioning the importance of the hippocampus, that area of the cerebral cortex that bears the name of the little seahorse due to its shape. It is the place of convergence of all information decoded in sensory areas. This structure facilitates the association of information from different regions of the cortex, for example by establishing a link between an odor and a lived experience.
From the hippocampus, the information follows a circuit called “Papez circuit,” which makes them pass into other structures of the limbic system – which is sometimes described as the “brain of emotions” – just to return “remodeled” to the hippocampus. Thus this information will eventually become long-term memories (see point 2), ceasing to redo the Papez circuit and definitively leaving the hippocampus to be encoded in the cortex regions specific to each sensory system – these same regions from which are derived the sensory information at the base of memories (see point 3).
My memory is “truer” than yours is!
Why don’t we have quite the same memory of a situation as others that lived the same events? Or why can our perception of memory be felt differently over the years? It is that first and foremost, a memory is a story that is told. This is not a faithful recording, but a reconstruction of a personal experience made of various elements – sensory, spatiotemporal, emotional, etc. – which, although recorded at the same time, have been stored in different places.
To use a metaphor of a book, when one remembers a memory, the brain does not have access to a “book” of this memory; it must instead try to find as many “pages” as possible having been “printed” in the same time. This scattering means that the memory will not necessarily be exact or immediate. To this must be added that the provisions in which we find ourselves recalling the memory – the nature and the context of the recall as well as our emotional state – will give it a particular hue.
Moreover, that memory works by associations, in the sense that one thing reminds us of another, then another, and so on! Thus, each one follows a path that is only his own to return to the footsteps of his memories.