Long-Term Memory
“the reason our brains have remarkable capacity for memories is that memory is actually for the future."
According to John Gabrieli, Grover Hermann Professor in Health Sciences and Technology and Cognitive Neuroscience at MIT, “the reason our brains have remarkable capacity for memories is that memory is actually for the future. It’s a way we learn about the world so that we’re more competent, more skilled, and more efficient the next time we encounter a task. And so, while memory is of the past, it is a tool for the future.”
Much of the time, we need to store information only briefly - while dialing a phone number or reading a paragraph from beginning to end. The brain accomplishes this with short-term memory, which holds data for seconds to several minutes.
But there are limitations with short-term memory. First, it can only hold about four unfamiliar items at a time and eight items if they are relatively familiar.
Second, information is quickly lost from short-term memory. Researchers have established that short-term memory data is lost in approximately five to twenty seconds unless immediately acted upon.
For example, if someone speaks to you before you’re able to dial a telephone number, you will probably forget the number unless you do something with the number. This doing something with the information is known as “mental rehearsal.”
During mental rehearsal, an “active buffer” is established. This is a place where information is maintained by continuously repeating, e.g., a phone number. The repeating of information is called the “articulatory loop” recurring every 1.5 seconds.
In other words, to retain information in short-term memory, data must continuously be repeated every 1.5 seconds, and done so indefinitely. When the “articulatory loop” ends, the information is immediately forgotten and becomes extinct.
The most efficient method to retain data for a longer time is to transfer it to long-term memory.
Metaphorically, long-term memory is an archival library where data is filed for retrieval and passage of time does not dim this system.
In many ways, what we know is who we are – we know our names, our loved ones, the values we hold, the abilities and needs we have, the facts of the world we inhabit. We knew none of this at birth – we came to know all of this through the making of memories. Long-term memory determines who you are, what you can do, and how you see your world. Every mental operation you perform depends on easy access of information you acquired earlier in your life. You find an experience meaningful because of its relationship to what is already in your mind.
Three stages of making a memory
Encoding - Storage - Retrieval
Making a Memory
According to Gabrieli, there are three stages involved in making and encoding a long-term memory and it is a multistage process unfolding over time.
Encoding is the initial stage when data from an experience or bits of factual information are simply encoded in the brain. In this stage, utilizing our senses, the brain selecting what happens in our environment and records the ongoing experience.
The next stage is the storage when key elements of the experience are selected, connected, and maintained for storage in designated areas of the brain.
In order to improve the storage of information, the information undergoes a process called consolidation. During consolidation, memories are integrated with other experiences and facts into the framework of things you know. The consolidation process establishes memories more securely making them less subject to misremembering or forgetting.
Lastly, the final stage is retrieval, where stored knowledge is found and implemented to help us function efficiently in our daily lives.
John Gabrieli explains the 3 stages of memory.
However, there are conditions surrounding encoding and storage of information that determine how readily we can retrieve and recall a memory. For instance, we are more likely to remember a situation, face, or fact if we paid close attention to it at the time, had a strong motivation to remember it, or was enhanced by an emotional or novel event.
Other factors affecting the efficiency of long-term memory is the sheer difficulty of loading information into the system, efficient encoding strategies that enable input to be fully processed and interpreted and related to what is already known, and the need to use retrieval strategies which enable ease in accessing stored memories.
In summary, it is best to remember that for true learning to occur by storing information for retrieval in long-term memory, the mind must be active by acting on new information. In other words, the mind has to do something with the information to make it memorable before it disappears.
In order to improve the probability that the mind remembers an experience and successfully retrieves information, the learning must be made meaningful, novel, or tied to our emotions. For instance, I’ll guarantee you remember more about your last vacation than your last faculty meeting.
The Grand Central Station of Memory: The Hippocampus
The hippocampus, sometimes referred to as the Grand Central Station of Memory, is located near the center of the brain in a region referred to as the Limbic system. Mainly it is responsible for converting short-term memories into longer-term memories and for the storage of memories for various lengths of time. The hippocampus works seamlessly with a region within the Limbic System, the amygdala. The amygdala, which is anterior to the hippocampus, intensifies a memory by adding an emotional component to it. The coordination between the two brain regions attaches emotion to an activity or event thereby improving the encoding process of hippocampus neurons, and thus making it easier to retrieve the experience. Memory wise, this is useful because it allows a person to more easily remember events that were “emotionally stimulating.”
How long before a short-term memory becomes a long-term memory?
The famous patient H.M., discussed in a separate section of the website, yields some insights into this topic. As a result of H.M.’s surgery to relieve the effects of epileptic seizures, he not only lost the ability to convert experiences into short-term memory but also the ability to recall past experiences. He had what is referred to as retrograde amnesia, a loss of memory of the past.
But how far back could he remember? Was his long-term memory completely gone? Researchers questioned H.M. about events that occurred within three to seven years prior to his surgery, with no recall. But when questioned about events in his early childhood, H.M. had perfect recall of those experiences. Upon further investigation, it was determined that his long-term memory was intact up to the eleventh year before his surgery.
The ramifications of this research are critically important for educators. Unfortunately during his surgery, H.M. lost his hippocampus, the region of the brain involved in converting short-term memories into longer-term memories. If the hippocampus was involved in all memory activities, its complete removal should destroy all memory abilities, thereby wiping his memory clean but this did not happen.
John Medina, author of the best-selling book Brain Rules, explains that, “the hippocampus holds on to a newly formed memory trace for years, not days, not months, and even a decade or more. System consolidation, that process of transforming a labile memory into a durable one, can take years to complete. During that time, the memory is not stable.”
Watch John Medina talk about H.M.
Neuroplasticity: How the brain is capable of change
When I was in college in late 1960s, I was taught that the brain was immutable from birth, with a certain number of brain cells and fixed neuronal circuits. The only changes thought to occur were the loss of brain cells and a reduction of brain volume. It was believed that once a person reaches adulthood, their cognitive abilities are immutable. But beginning in the early twentieth century, that theory has been contested by evidence suggesting that the brain’s abilities are in fact malleable and plastic. According to this principle of neuroplasticity, the brain is constantly changing in response to various experiences. New behaviors, new learnings, and even environmental changes or physical injuries may all stimulate the brain to create new neural pathways or reorganize existing ones, fundamentally altering how information is processed.
Brain Break
1. What are the three stages of making a memory?
2. The brain area associated with long-term memory is?
3. After birth, the brain is composed of a certain number of brain cells and fixed neuronal circuits. True or False
Answers. 1. Encoding, Storage, Retrieval: 2. Hippocampus: 3. False
Long-term potentiation (LTP) is how we remember information and is an example of neuroplasticity.
Learning requires strengthening the affinity between neurons through a dynamic process called long-term potentiation (LTP), the fundamental mechanism of memory. When the brain takes in new information, the demand naturally causes activity between neurons. The more activity, the stronger the attraction becomes, and the easier it is for the signal to fire and make connections. This process is the fundamental principle of the retaining and retrieval of information, the neural process called learning.
The initial activity between two neurons causes the receiving neuron to reconfigure its receptors. If the firing continues, the neuron produces more building material for the synapse, and it is this strengthening of the infrastructure that allows the new information to develop as a memory.
Suppose you are learning a new vocabulary word. The first time you hear the word, circuits are created between two nerve cells. If you never practice the word again, the attraction between the two nerve cells naturally lessens, deteriorating the signal. You forget.
Explaining this concept, Medina posits that “these physical changes result in the functional organization and reorganization of the brain. This is astonishing. The brain is constantly learning things, so the brain is constantly rewiring itself.”
Example of a neuron sprouting a new dendrite as a result of LTP.
How the brain changes due to excessive activation is another example of neuroplasticity.
“The brain acts like a muscle: The more activity you do, the larger and more complex it can become. Whether that leads to more intelligence is another issue, but one fact is indisputable: What you do in life physically changes what your brain looks like.
One of the most dramatic examples of neuroplasticity at work comes from a 2000 brain scan study on London taxi drivers (Maguire et al., 2000). In order to earn a license, London taxi drivers typically spend about two years learning to navigate the city’s serpentine streets. What mark, the study’s researchers wondered, did this long, rigorous period of training leave on taxi drivers’ brains? Under the scrutiny of fMRI scans, 16 male taxi drivers were revealed to have larger hippocampuses than a control group of 50 healthy males. And the longer the time spent as a taxi driver, the larger the hippocampus tended to be. As a brain area involved in memory and navigation, the hippocampus seemed to have changed in response to the taxi drivers’ experiences.
When scientists mapped the brain areas that receive sensory information of string musicians who practiced a skill year-in and year-out, they found the area larger than that in nonplayers. They also found that the area of the brain activated on hearing piano notes is roughly 25% larger in pianists than in non-musicians.
Similarly, people who read braille have larger hand sensory areas in the brain.
Khan Academy on Neuroplasticity
Nobel Prize awarded for understanding how memory works on a cellular level
Eric Kandel, Columbia University College of Physicians and Surgeons, shared the 2000 Nobel Prize for Medicine by confirming this process of cellular change. He demonstrated that repeated activity and practice causes the synapses to swell and make new connections. To this point, Kandel showed that when people learn something, the wiring of the brain changes resulting in the physical alteration of the brain structure.
In summarizing his work, Kandel state that short-term memory had been linked to functional changes in existing synapses, while long-term memory was associated with a change in the number of synaptic connections.
Watch a 2:08 minute video as Eric Kandel discuss his book In Search of Memory.
Take away thought: Most of the knowledge we get from disconnected facts that are never applied leaves us very quickly because there was a breakdown in either of the three stages of memory; encoding, storage, or retrieval.
The great cognitive scientist - Guido Sarducci - reminds us of this fact when he invented the 5-minute university (total tuition is $20 and includes cap and gown rental and a Polaroid of your graduation). Obviously, much of what we learn in an inert way leaves us very quickly.