Memory and its Myths
Memory is often understood as an informational processing system with explicit and implicit functioning that is made up of a sensory processor, short term (working) memory and long-term memory. It remains that Memory is the faculty of the brain by which data or information is encoded, stored and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. Past events need to be remembered in other to express self in language, relationships or personal identity. Memory loss is then described or defined as forgetfulness or amnesia.
How many know that our stream of consciousness starts with memories at early age, perhaps as early as three or four years of age. It looks like it is the way we forge memories. What we remember from the past, becomes a scaffold for future relationships or events shaping emotions to come. We may tell when the story of a scene and images populate our minds. Some memories fade away with time but others come back to haunt you and we are able to remember the details of a given place or the recollection of certain facts. Can we try to understand the neurobiology of the memory…?
I still remember the “game of Kim” we used to play as boy-scout in the St George’s troop, at “Petit Seminaire College St Martial” in Haiti when each member of the troop was facing a table full of items to try to memorize the most of them. The object of the game was to remember the most articles exposed on the table and then to crown a winner.
I had also a vivid recollection of one Christmas Eve evening where Richard my brother and Stanley and Tony, my childhood friends and I, were planning to enjoy the moment while the public was in the street chopping for a Christmas tree. We had our ‘Fanals” and the little cars we build up with wheels, ready to explore the street (Lalue =Avenue John Brown). We decided to rest our cars and positioned ourself in strategic locations in order to shoot “clips”. We made many victims that night until we got caught and punished by one of the victim’s husbands. In my dreams, this night will come back to haunt me so many times, but the details of the memory remained vivace and accurate to a point that I had the impression that I was re-living the experience again and again. Occasionally, I will experience night sweats.
We learned our lessons and were punished that night with the expectation of receiving a bicycle from Santa Claus under the tree. Brief, I had re-experienced this adventure in my dreams, so many times, like it was for me a culminant moment in my life. We were then eight or ten years old but, 30 or 40 years later, why do I continued to remember that evening, vividly with so many details and so much accuracy…? while we had so many other interesting adventures to enjoy… Why did the souvenirs of that evening returned to hunt my dreams…?
The recollection of such autobiographical episodes consists in an “episodic memory “referring to information that is encoded along a special and temporal plane while “semantic memory” refers to memory that is encoded with specific meaning. Memory is not a perfect “processor’ and information can also be corrupted by pain or physical damage to some area of the brain like the hippocampus… or because of the decay within the long-term memory over time or brain damage affecting the memory etc.
This is only in the past 50 years that researchers have begun to understand the neurological and physiological “meaning” of human Memory. It can be understood as a processing system of information doted of a sensory processor which represent the short-term memory and a long-term memory functioning as a neuron allowing information from the outside world to be sensed under the form of chemical and physical stimuli. This working memory serves as an encoding and retrieval processor able to store data.
Memory does not reside in one corner of the brain rather it is a complex system involving many areas working to make sense of life experience.
Neurobiologists have identified two main classes of long-term memory at work in the brain: an “Explicit” (declarative) form which is processed in the hippocampus and the medial temporal lobe with conscious recollection of names, dates events, peoples, places etc and an “Implicit” form which encompass unconscious, procedural and routine motor tasks such as trying to walk or to put a shoe, processed in the Cerebellum (motor activities), the Striatum (voluntary movements) and the Basal Ganglia (?) and Mamillary bodies(?). Brief, the hippocampus is believed to be involved in spatial learning and declarative learning while the amygdala is thought to be involved in emotional memory.
The ability to look at an object and remember its shape in a split-second of observation or memorization, like in the “game of Kim” I described earlier, is an example of sensory memory which is out of cognitive control because it implies an automatic response. George Sperling in 1963 reported his conclusions after placing 12 letters arranged in 3 rows of four in front of individuals: this has allowed him to conclude on their ability to remember approximately 12 items but their memory degraded quickly and the participants were unable to report their observation on the letters. The study helped to conclude that there were three types of sensory memory: an Iconic memory (stores image perceived for small duration), an Echoic memory (memory of sounds of short duration), and a Haptic memory (tactile memory). Rehearsal will not allow you to improve your score.
Let us be more specific and define different type of Memory so we can comprehend better. By definition, all memory falls in two categories either memory is “declarative” or “implicit” but can be of a short term(30mns) or long term (may last forever).
Short-term memory is also called “working-memory” because it imposes periods of recall extending to several seconds to a minute. George A Miller who worked at Bell Laboratories in 1956 conducted experiences concluding that the capacity of short-term memory was a 7 to 2 items in a book he named “the Magical Number 7 to 2. This short-term memory can increase through a process called “chunking” like grouping numbers of a telephone remembering area code and chunk the other numbers. Short-term memory seems to rely more on an acoustic code for storing information than a visual code. Memory of acoustic components may also enhance memory of written language.
Declarative Memory (Explicit) is a system of conscious memories requiring effort like remembering items on a grocery list or a phone number or even a friend face or an article in a book. It is divided in a Working Memory (1) which represent a short-term system for storing and processing for a short period of time like 30 seconds and after that the information begin to decay. Example in calculating a tip in a restaurant, or remembering a lecture but not too many tasks like four or five items at the time. Next, an Episodic Memory (2) which represent a long-term memory for past event such as a family reunion or a road trip with friends or a football or basketball game watched on TV. Also, a Semantic Memory (3) which represent also a long-term memory for learning and remembering name of presidents or countries and their capitals.
Implicit Memory (Non-declarative Memory) is a long-term memory that unconsciously influences our perceptions and behavior unconsciously. It can be divided in three components: A Procedural Memory (1) dealing with motor skills allowing us to complete tasks like riding a bicycle. A process of Priming (2) where when exposed to a stimulus, it will trigger a mechanism of response such as the association of the color Yellow and the banana. A conditioning memory (3) similar to what we have learned with the Pavlov reflex in medical school. When exposed to a stimulus, one will react to form an association between ideas and memories but eventually like the dog in this experience, it reminds him that is the time to eat.
The modern science of memory begins in the late 1950’s when a patient called Andre Molaison, a former assembly-line worker from Connecticut, suffering from epilepsy, agreed to try an experimental procedure to control his seizures. He agreed to have part of his brain, including the hippocampi and part of the temporal lobes, removed. The study was reported by Brenda Miller, a neuropsychologist at McGill University as a huge breakthrough. Surprisingly, he developed an “antegrade amnesia” allowing him to remembering many events before his surgical procedure but he was unable to form any new episodic memory. Scientists concluded that the hippocampus was necessary to form any new episodic memory.
The hippocampus is nestled deep within the brain behind the temporal lobes. The pathway “ventral visual stream” is used to deliver information. My childhood memories were encoded by my hippocampi and I was able to reconstruct and associate the images recorded. The storage in sensory memory and short-term memory has strictly a limited capacity and duration because information is not retained indefinitely. Encoded through a complicated interplay of electricity and chemicals where nerve cells (neurons) connect with each other via a gap known as synapse where electrical pulses fire up, triggering the exchange of messengers (neurotransmitters).
It is the same neurons from the original experience that is activated when we recall a memory: they duplicate the moment.
In a human brain, there are more than 100 billion of neurons passing signals and creating bounds. The brain re-wires itself by a phenomenon called “Neuroplasticity”. A study on taxi-drivers in London was performed showing that their hippocampi become larger the longer they were on the job, navigating the city’s streets. This involves their spatial memory.
A neuroscientist, Eric Kandel, at Columbia University won the Nobel Prize in Physiology and Medicine for his work on the biochemical mechanisms of memory storage. Basing his assumptions on the Milner’s work, he chose in 2012 a simple animal, an “Aplysia”, a snail with very large nerve cells to reflex tests stimulating their brain cells with electrodes. He discovered that the snail response could be modified by learning. He used this model to study the conversion of short-term memory to long-term memory. He also found that learning strengthened the brain. As described above, the short-term memory can easily hold the 7 numbers of a telephone number but it is more difficult to hold the 9 numbers. Kandel found out that in learning the number, the synaptic connection strengthened.
Scientists also found out that unlike short-term memory, long-term memory requires the synthesis of new proteins. In the 1970’s, they finally believed that a neurotransmitter (serotonin) activates a messenger molecule known as “cyclic AMP or cAMP”. Later, in the 1990’s, Kandel labs discovered the protein “CREB” which played a key role in the long-term memory storage through the synaptic connections. It looks like another receptor AMP or NMDA is found inside the hippocampi enabling learning to potentially promote long-term storage of data. It was surprising also to see that more protein like CPEB may be responsible for creating long-term memory. It becomes surprising to see the resemblance between CPEB and the “toxic” prion-like protein found in Mad Cow Disease and Alzheimer. I would refer you to the previous AMHE newsletter # 262, which delt with this other pathologic entity. It has been suggested since, that long-term memory storage in humans may be maintained by DNA methylation or the mRNA or by the “prion” gene itself. By 2015’, it has become clear that long-term memory requires gene transcription activation and de-novo protein synthesis. More researches are on the way.
Long-term memory can store data for a much longer duration and potentially for a life span. The recording of numbers of a phone remains a classical example when 7 or 9 numbers needed to be remembered. Short-term memory encodes information acoustically while the long-term memory encoded it semantically. Many have found out how test subjects will have difficulty recalling a collection of words like (big, large, huge, great…) that has similar meaning in a long-term. The long-term memory is episodic and attempts to capture information based on “what, when, where…” and still being able to remember birthday parties or weddings.
Short-term memory is supported by transient patterns of neural communication depending on the regions: frontal and pre-frontal or parietal lobe etc. Long-term memory is more stable and can produce more permanent changes in neural connections through the brain. The hippocampus is essential for the learning and consolidation of information for short-term to long-term memory. Studies on Malaison are becoming questionable because a new post mortem examination of his brain has shown that the hippocampi were more intact that previously thought. Many believe that the hippocampus may be involved in changing neural connections for a short period after the learning. More the role of the Amygdala will have to be determined.
By contrast, it has not been established yet the total capacity of the Long-term Memory which can certainly store larger quantities of information… Researchers have shown that direct injections of cortisol or epinephrine help in the storage of recent experiences. This appear to be the same for the amygdala. The hippocampus is important for memory consolidation as well and receive input from different parts of the cortex and send back output to different parts of the brain as well. Hippocampal damage may cause also memory loss and problems with memory storage, including retrograde amnesia with the loss of memory or recent events. Amygdalar damage may cause emotional memory loss.
Studies on the genetics of human memory investigated many genes in humans and animals. The association of APOE with memory dysfunction in Alzheimer disease is well known. Other genes or protein like KIBRA with memory loss over a delay period suggesting that memories are also stored in the nucleus of the neurons. Several other genes and proteins or enzymes are being studied for their association with memory. Long-term memory unlike short term memory is dependent upon the synthesis of new proteins within cellular bodies as transmitters or receptors or in the synapse pathways between neurons. Examples of LTP in long-term memory or the enzyme Protein Kinase C (PKC) in the synapses for long-term memory or BDNF… etc
Studies in childhood amnesia have demonstrated that infants as young as six months can recall information and as they grow older, they can store information for longer periods. They can also re-call information over the short term. It is only by 9 months of age that one can recall the actions of a two-step sequence… and at 14 months, a three-steps sequence… The reason appears to be clear that in that difference of age, it looks like the “dentate gyrus” of the hippocampus and the frontal components of the neural network may not be fully developed at an earlier age like 6 months. In fact, the term “infantile amnesia” refers to the phenomenon of accelerated forgetting observed during infancy due to a rapid growth of the brain during this period as described by the neuroscientist Dr Jee Hyun Kim.
Studies in aging deal with memory loss especially in Alzheimer’s disease, but different from memory loss due to aging. Research has demonstrated that individual performance on memory tasks that rely on frontal regions declines with age. Older adults tend to exhibit deficit on tasks that involve the temporal lobe, source of their memory tasks other may use recollection from a book or manage their problems with prospective memory in using an appointment book by example or DNA damage or other psychosis like Korsakoff syndrome or other memory dysfunction encountered in disease like COVID-19… etc.
Knowledge of memory disorders has allowed us to understand better memory. Loss of memory (Amnesia) can result from extensive damage to the temporal lobe, hippocampus, dentate gyrus, amygdala, thalamus or the mammillary bodies etc. Other diseases like Alzheimer’s and Parkinson, Hyperthymia syndrome can all affect the autobiographical memory, or Korsakoff syndrome or psychosis as an organic brain disease with memory loss and shrinkage of the neurons in the pre-frontal cortex. Other viral disease like SARS-CoV-1, MERS-CoV, Ebola and even Influenza viruses can produce the symptoms of amnesia.
Stress has a significant effect on memory formation and learning. The brain releases hormones and neurotransmitters (Glucocorticoids, Catecholamines) in response to stressful situations which affect the memory encoded in the hippocampus. Chronic stress has shown the way neurotransmitters are produced to impact the hippocampus in rats’ brain. Post-traumatic stress situations in a life experience can be relieved when the memories of a traumatic event can be situated and delt with. Glucocorticoids released during stress can cause damage to the neurons located in the hippocampal region of the brain. The CA1 neurons found in the hippocampus can be destroyed, forcing the re-uptake of the glutamate and decreasing the release of the glucose… examples in the prisoners of war (PTSD) or in child abuse cases…
Sleep affect memory consolidation. When one does not get enough sleep. It become difficult to learn. During sleep, the hippocampus replays the events of the day for the neocortex, then the neocortex reviews them and processes the memories to move them into long-term memory. Scientists believe that this is one of the primary functions of sleep. There is so much to discover on this topic relating on the power of Memory.
There is a certain lifestyle able to affect your memory and I would like to touch the matter a little. We saw what a lack of sleep can do to the memory but there are other unexpected conditions to watch as well including medication, diet, etc. By example a non-functioning thyroid will render a patient hot or cold, anxious at time and depressed, lagging on the memories, but the thyroid hormone has no interaction on the brain and the memory. The same goes with the menopause and the hot flashes when a woman can become unable to remember names or stories, but there again. These hormones have nothing to do with the brain.
Anxiety, depression, stress and even bipolar disorders can disrupt the neural pathway taken by the memories. The severity of the memory loss depends on the severity of the mood disorder. Smoking can damage the brain by impairing it brain supply. Even a cold or any infection can mess up your ability to think. Vegetarian diets are lacking vitamin B12 responsible in keeping the nerve cells healthy and functional. B12 is also enter in the fabrication of the DNA.
Some literature reports the well-being of green tea on the fact that substances like L-theanine has the ability in increasing the neogenesis in the hippocampus improving short term memory and learning. Exercises have also a primordial role because the more you sweat, the more your memory improves it function.
To conclude, I would urge anybody who enjoyed this article, to find time for reading with a special attention, the classic book of Kandle: “In search of Memory”. I just would like to echo some of his words: “Has it ever struck you…that Life is all Memory, except for the one present moment that goes by you, so quickly that you hardly catch it going…?” Recently, on Mother’s Day, I felt the” power of Memory” while the circumstances bought to light the souvenirs of nice moments passed in company of my beloved mother, Claire Laurent Coles.
May this paper help anybody appreciate this God given gift. we all have available in us.
Maxime J Coles MD
Boca Raton FL
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