“I can remember everything that happened that day as if it were yesterday… although ten years ago, I can remember perfectly the taste of that food, for I will never forget where I was at the time.”

Most of us sometimes find it hard to remember what we had for dinner the night before or what perfume we chose before leaving the house, but perhaps we will recall in detail the menu of our wedding day (a designated date) that took place several years ago. So why are some memories engraved in stone and enduring unforgettable over the years, while others are fragile and disappear in minutes?

In a 1977 study, Roger Brown and James Kulik of Harvard University published that 79 out of 80 Americans interviewed vividly remembered the circumstances in which they were 14 years earlier when they heard that John F. Kennedy had been murdered. These results have been replicated in numerous studies that have studied similar events of singular importance, observing the characteristics of persistence or accuracy of memories formed in certain circumstances. this type of memory is called flashbulb.

Remembrance Memories

Some memories are much more vivid than others. With the name flashbulb, we refer to particularly vigorous memories that were generated in response to a unique experience with a high emotional charge. For example, the attacks of 11 September 2001. We all have very intense personal memories related to important events in our life, such as an accident or a wedding. In other cases the persistence of memory requires attention and effort on our part as the learning of different subjects during academic formation.

The numerous data reveal that events that have been associated with moments of high emotional charge tend to be spontaneously remembered with a particular intensity. But in other cases, the formation of memories is not carried out unconsciously, as it requires effort on the part of the individual to be able to retain certain information. In other words, their persistence is only achieved through repetition. How many times did we have to go over the multiplication table or the list of European capitals before we could remember them?

When we stop to think about what is this about memories? There are numerous responses and issues related to the topic. Science has focused for many years on being able to locate memories in the human brain and today there are many results obtained thanks to the technological advances of the time.

Thus we could define memory in a general way as the ability of the nervous system to retain information about past experiences, so that future behaviors can be conditioned. However, the concept of memory is much more complex than this, since today we know that it encompasses very diverse capacities and can distinguish different types of memory:

  • Explicit or declarative memory: such as our memories of people, places and things.
  • Implicit or procedural memory: which includes different forms of unconscious, motor, or perceptive learning.

In turn, these types of memory require the participation of different neural circuits and are located in different regions of the brain. But reaching this conclusion has not been easy. Through the study of patients with very different brain lesions, laboratory animal experiments and surgical and pharmacological techniques, it has been possible to identify the anatomical substrate of different forms of learning and memory in humans, ending with the initial idea of a completely delocalized substrate that was maintained at the beginning of the 20th century. We can therefore conclude today that the brain is a conglomerate of specialized circuits that perform different functions.

After some theoretical data let’s take an example:

Neuropsychologist Brenda Milner was working on one of the most relevant cases in the history of the neuroscientist clinic, particularly with a patient known as H. M. who appeared to have a major brain injury to the temporal lobe.

H.M. The Story Of A Man Without History

At the age of 27, H. M. underwent an experimental and risky surgery to cure him of the increasingly frequent and intense epileptic seizures he had suffered since childhood due to a bicycle accident. The operation consisted of surgical removal of the region of the brain where doctors considered that the focus of his epilepsy was found, a part of the temporal lobe that included the hippocampus.

The results of the intervention were surprising: after the operation, H. M.’s brain had lost the ability to form new memories. In the words of the responsible surgeon: “we tried to end his epilepsy, but we ended his memory. The operation took place in 1957; in the following decades H. M. was in good health and underwent numerous neurological and psychological studies.


The research revealed that the patient was unable to form new memories of the people he had met after the operation, including the nurses he saw daily and so continued until his death in 2008 at the age of 82. What is more interesting is that, unlike what is observed in episodes of amnesia classic, most of the memories of H. M. previous to the operation, remained intact.

Moreover, although his brain was unable to acquire new declarative-type memories, it was not closed to other forms of learning, such as acquiring new motor skills. In this way it was shown that the different types of memory were housed in different anatomical substrates.

This case led to the identification of the temporal lobe in general and the hippocampus in particular as an essential component for the acquisition of new memories about people, events or things, i.e., explicit or declarative memories. However, once memory has been acquired and consolidated, the hippocampus is no longer necessary. By mechanisms that are still unknown, there is a transfer of information from the hippocampus to cortical centers. Therefore, hippocampal lesions do not affect consolidated memories prior to damage.

In addition to this progress, other studies have been able to elucidate neural circuits that underlie other types of memory. For example, amygdala, Striate, or different regions of the cerebral cortex play a key role in emotional, motor, or procedural memories. But what are memories made of? what should we look for when we talk about them?

Ramón y Cajal

The identification of the physical nature of Memories has been a recurring theme of study throughout history, but it was not until the late 19th century that the first hypothesis loaded with scientific validity was postulated based on the intuition of the Aragonese neuroanatomist Ramón y Cajal, father of modern neuroscience and Nobel Prize in medicine and Physiology in 1906. By 1894, the author stated that:

“Mental exercise facilitates the further development of nerve structures in the parts of the brain in use. Thus, pre-existing connections between cell groups could be reinforced by the multiplication of nerve terminals’’

At present, this hypothesis explains the vision of the problem in question. The majority of neuroscientists think that the mechanisms of synaptic plasticity (the ability to modulate or change the strength of connections between neurons, the synapses, and consequently the properties and functions of neural circuits in response to external stimuli and previous experience) represent the cellular substrate for the formation of the different types of memory: from the simplest forms of non-associative learning that we observe in sensitizations in laboratory animals, to the elaborate forms of declarative memory in humans.

It is admirable that Ramón y Cajal could infer that idea from what was observed in the static images of their preparations in microscopy. Finally, Ramón y Cajal’s hypothesis on synaptic plasticity found a more formal definition fifty years later in the words of Donald Hebb (1904-1985), a recognized Canadian psychologist whose postulate is now considered the most reasonable explanation of what happens in our brain when we learn: “when the axon of cell A excites cell B, and repeatedly or persistently intervenes in its activation, some type of metabolic growth or change takes place in one or both cells…..

Fun Facts : Memoirs Of A Snail. When Size Matters

Aplysia californica

The sea snail Aplysia californica has earned a prominent place in the history of Neurosciences. Its nervous system, consisting of about 20,000 neurons organized into a dozen ganglia, is very simple compared to the more than 10 billion neurons that make up our brain. Despite such simplicity, the snail exhibits a variety of Innate and acquired behaviors ranging from non-associative learning to conditioned learning. Therefore, Eric R. Kandel of Columbia University has devoted much of his scientific career to researching the cellular and molecular basis of these basic forms of learning. The accessibility of your nervous system and the large size of your neurons, the largest observed in the animal kingdom, have enabled you to identify in great detail the neural circuits that regulate specific behaviors and to study how learning and memory formation affects and results in physical changes in specific connections within these circuits. Much of what we know today about the cellular and molecular bases of memory is due to this animal. Despite the difference in number of neurons and complexity, it appears that the basic molecular mechanisms underlying learning and memory in this, are highly conserved in mammals.

Lability Of Autobiographical Memory

A scandal was broken out at Helmut Schnatz’s conference a few years ago. Among those attending the event were many elderly people from Dresden, direct witnesses of the horrible attack suffered by their city on 13 and 14 February 1945. Excited, they said that, after the collapse of the buildings, the British planes had gone to hunting, in low flight, those who fled from the flames towards the banks of the Elbe or the Great Park. Schnatz, a rigorous historian, patiently explained that the facts belied that memory.

The bombings raised such a column of fire that it was impossible for pilots to fly over the city at low altitude to attack people one by one. The analysis of the attack plans and parts of the British air raids has also failed to provide any evidence of such man-fighters. Although he explained it with caution and prudence, the researcher considered the history of low flight a myth that is perpetuated until today in the memory of many citizens. But the listeners were indignant, for had they not seen with their own eyes the ” silver Mustang fighters” and the people who fled despondently?

Autobiographical Memory

Memories, though false, contain a great emotional density. They have become so important to them that they no longer want to lose these feelings and other associates. Ultimately, these are events that were decisive in their lives and they could never forget them. Paradoxically, this intention is likely to transform what has been lived in a thousand ways, since any evocation of a memory also results in its recast storage. It archives the context of each evocation situation, so that the original memory can be enriched or corrected with new nuances and focus or even transferred to certain aspects.

Who comments with other participants, shared events, accuses the influence of others in their personal retrospective. For example, in cases of experiences as hard as a war entails, sociologists observed that the stories are standardized in the format in which others also remember it. Many of the transmissions of the events hold a similar pattern, seemingly all people would have lived the same in a certain phase of their lives.

This brings to light that witnesses of war experiences can present very different memories than those documented in history. The inhabitants of a bombed-out City are formed in communities of remembrance that exchange stories and at the same time modify and configure them until they all have a background of similar stories. Certainly, all of them are based on comparable experiences, yet they have often been modified, adulterated and created in communication.

Memory scholars know that reports of singular episodes and even complete developments of events can be integrated into pre-existing memory content. False memories can be fed from very diverse sources that transcend what you have lived by yourself: narratives of other people, novels, documentaries, films, dreaming and fantasies. It is a phenomenon of amnesia from sources: the event is remembered as such, but the source from which the memory comes is confused. Over time, this tendency of the brain to remember the experiences of others as part of its own biography intensifies.

But can these eyes be wrong? The relevance of such imported reminiscences is that: “they are almost alive in front of the eyes as if they had happened yesterday. Thus the visual representations of past events, subjectively possess the greatest strength of conviction. Events, in order to be stored later in memory, do not need to pass through the retina first.

The neural systems of processing visual perceptions and those of the fantasized and imagined overlap partially. Stephen M. Kosslyn , of Harvard University, demonstrated in 1995 that the primary visual cortex it is activated in a similar way when the probands see objects and when they are only represented.

Events are welcomed in one’s own history with such ease as they are better integrated into the general sense of substance. For example, the direct experience of war leaves deep emotional traces behind it. This was demonstrated by Joseph LeDoux: firm synaptic connections are established between the nerve cells of the amygdala (the core of emotional connections), which trigger a rapid affective reaction.

In this way, certain stimuli that recall the primordial experience, promote the release of neurotransmitters in the brain, and thereby provoke the bodily alarm signals that are linked with the Memory Program (you start to tremble, sweat, be afraid and seek protection).

Consciousness can assign this trace of emotional memory to very different events, not lived, although perfectly assimilable to our web of feelings. Traumatic memories need not be “truer “or” more authentic ” than others, but the feelings attached to them contain the emotional imprint of the event of that time.

The crux of the matter is that contemporary witnesses cannot come to know for themselves whether something is a true or false memory, for the person who remembers them, they both feel entirely the same. Thus, although witnesses have very different memories from those documenting historical events, it does not mean that they lie or supplant yesterday, but that when they keep an image, they do so with a strong emotional charge, which will hardly change with what they learn later.

It should be added that such conflicts between memories can be transmitted through generations. Thus the oral transmission of the past shows that even though grandfather or grandmother tell a certain story, listeners come to their own version of the story. It is as if it were a kaleidoscope, where the elements and features of the stories are transformed into a new constellation. Therefore each one goes to include in the structure of the narration his own feelings, forming different collage based on the identity of the one who remembers.

A Higher Memory

If we think for a moment, what did we have for breakfast this morning? Surely it is not the slightest effort for us to answer the question correctly. But could we say what we ate on September 29, 2003, once we were awake and showered? Certain people are able to satisfy that curiosity. From a specific moment of their childhood or youth they are able to describe with hairs and signs every moment of their life. They know by heart that day of the week is a specific date of the calendar, what they did in that day and the news they read in the newspaper.

We call this superior Autobiographical Memory or hyperthymesia, whose denomination comes from the Union of the two Greek terms: Hyper, which means “above”  and  thymesia, ” remember. There is a great difficulty in investigating the origin of such capacity as a small number of people are known to have it. Science is trying to find in its brain the secret of such amazing ability. Let’s see an example:

Jill Price

In 2000, the history of this syndrome began with a woman, who at that time was 34 years old, searched for online  help with James McGaugh, of the University of California in Irvine.  Jill Price sent the researcher an e-mail telling him of her unusual ability, which allows her to preserve the earliest memories of her earliest childhood and store in the brain every day of her life since February 5, 1980.

Jill Price

As she explained, the memories of the past do not come to her when she wishes to consciously remember, but they literally overwhelm her every time she encounters a date. At first glance many people would dream of possessing such a gift, but Price finds it a burden.

McGaugh was fascinated by the case. Over the five years after reading the young woman’s message, she studied the matter thoroughly. It was based on multiple intelligence and memory tests to check the patient’s knowledge of specific days of the past.

As he found out, Price’s memory stood out above all in relation to the calendar: in ten minutes she was able to date every Sunday of Easter between 1980 and 2003, making a mistake in only one of them for two days; she also remembered what happened in her life each of those days. McGaugh’s team contrasted some of that information with the personal diary entries that this woman has meticulously written since she was a teenager.

Price’s brain also stores events of public significance with their respective dates, as long as they interest her personally. This was observed by researchers when asked about relevant events collected in a book on contemporary American history. The patient got all the dates right, except for one: the day of the occupation of the US embassy in Iran in the late seventies of the last century. It was subsequently found that the data in the volume was incorrect. Price was right.

McGaugh and his team found that this unusual ability was not based on a mental calculation of calendar dates as described in some autistic people with sage syndrome or savant. These subjects are able to calculate accurate data within a period of up to 40,000 years. Price, on the other hand, only remembered facts since 1980: since then, hers autobiographical memory has worked mysteriously accurately.

In subsequent memorization tests, researchers discovered that this patient’s brain hid other enigmas: it was able to remember words with the same perfection.  Recognized 50 terms that will just show without mistakes. However, it obtained a below-average result in less structured tests such as reciting word list memory. The patient acknowledges that she often loses her keys at home, as well as that she points out many things from day to day so as not to forget.

Besides, contrary to what one might think, Price’s intelligence fits the average of mortals. It mainly costs her the tests of abstract thinking and anticipation related to the executive functions of the frontal lobe (which qualify the mental processes that serve for the flexible management and adaptation of human behavior; these include impulse control, action planning or emotional regulation). He never got remarkable grades during her student life and always needed to work hard, especially to memorize poetry or historical data.

At the moment there are no standardized instruments for studying hyperthymesia, which means that researchers have not been able to clarify the reason for this strange memory capacity. The studies that have been done in patients as Price have been based on methods devised in the beginning to evaluate patients with memory disorders. But what has been contrasted with control groups is that brain areas related to autobiographical memory are located at the time pole.

There are differences in a total of nine brain regions among which magnetic resonance tomography (MRI) has been found: the temporal lobe of the telencephalon  (lower and temporal medial spins or temporal pole), the unciform fascicle  and the frontal lobe. The unciform fascicle has been shown to connect the frontal lobe to the temporal and play a key role in autobiographical memory. There is a study of a patient who suffered an injury to the unciformed fascicle due to a bicycle accident, which caused him damage in that area and as a result the inability to remember past episodes of his life. However, semantic memory was largely intact.

The Regions such as the amygdala and hippocampus are also spoken of, which perform outstanding functions in this type of patient. The connections that exist between the two brain structures are more than usual and also facilitate remembrance: emotions have great importance in the ability to remember, so we recover events with emotional transcendence better than neutral stimuli.

The amygdala loads emotions into memories, thereby giving them great personal relevance.  But while it is true, the research still does not know the origin of this ability, so it is open to think whether these brain alterations are the ones that cause this ability or the regular use of this ability transforms the brain.



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