“Memory” is given its own section within Neurobiology, because it is fundamentally important in understanding the way our minds and bodies respond to traumatic events.
However, recent research has challenged the explanations of memory that we have accepted as fact for the last 20 years. I need to acknowledge this, that the information presented in the website is constantly being researched and, at times, revised. Neurobiology is such a new field.
This section will offer some explanations about the function of Memory and will attempt to offer research updates that suggest possible changes we will need to make to the ‘standard model’ of memory science.
What is “Memory”?
For people unfamiliar with the field of Trauma, it might come as a surprise to discover that the phenomenon we call “Memory” is core and fundamental to the condition we call Trauma. It’s therefore frustrating that there’s so much we still don’t understand about how memory works in the brain. Siegel devotes a chapter to exploring this question in his book The Developing Mind (see Resources list), and it is fascinating reading. I have reproduced here some excerpts from Siegel’s article in Healing Trauma, 2003, Eds Solomon & Siegel.
Reproduced from Dan Siegel’s article “An Interpersonal Neurobiology approach to Psychotherapy”, pp 1 – 56, in Solomon & Siegel, 2003.
Memory can be defined as the way in which a past experience alters the probability of how the mind functions in the future. Memory shapes how we experience the present and how we anticipate the future, readying us in the present moment for what comes next based on what we’ve experienced in the past. This broad view enables us to examine the findings of two aspects of memory and explore how their integration can promote well-being. Segregation of these memory functions, in contrast, may be seen as one aspect of the source of mental suffering.
Experience creates the activation or “firing” of neurons. This neuronal activation can in turn lead to alterations in the connections among neurons, the basis of neural plasticity. Throughout our lives we embed experience into memory via a first layer of processing called “implicit” or “non-declarative” memory. Before one and a half years of age, this early implicit layer of memory is the only form available to the growing infant. But even beyond that early age, we continue to create implicit memories but they are then often selectively integrated into the next layer of processing called “explicit” or “declarative” forms of memory.
Implicit memory involves the perceptual, emotional, and behavioral neural responses activated during an experience. It is likely that our bodily sensations are also a form of implicit memory, but these have not been formally studied in research paradigms. Mental models, or generalizations of repeated experiences called “schema,” are also a form of implicit memory. The brain also readies itself to respond in a fashion called “priming” in which past experiences shape the way we prepare for the future.
Implicit memory encoding does not require focal, conscious attention. A second crucial feature of implicit memory is that when we do retrieve an element of implicit memory into awareness we do not have the internal sensation that something is being accessed from a memory of the past. We just have the perceptual, emotional, somatosensory, or behavioral response without knowing that these are activations related to something we’ve experienced before.
The second layering of memory is called explicit and involves the two forms of factual (or “semantic”) memory and episodic (or memory for an episode of an experience in the past). Episodic memory has a sense of the self and of time. Both semantic and episodic memory appear to require focal attention for their encoding and when they are retrieved from storage into present awareness they do have the internal sensation that something is being activated from the past. The hippocampus may serve an important role in memory integration as it functions as an “implicit memory puzzle piece assembler” that clusters the basic building blocks of the various elements of implicit memory together into framed pictures of semantic and episodic memory. These framed pictures of explicit memory can then be further integrated into autobiographical memory, a function that may involve rapid eye movement sleep as our dreams integrate our past experiences, our daytime events, and our emotional themes of our lives.
This discussion of the nature and function of Memory is given a chapter in Siegel’s book The Developing Mind: how relationships and the brain interact to shape who we are (2nd Ed. 2012).
New Paradigms from current Research
The following article is a second-hand report via the BBC News website, and is not a scholarly article. It merely reports on some new research into memory encoding.
Rules of memory ‘beautifully’ rewritten
By James Gallagher
Health and science reporter, BBC News website, April 7th, 2017
The human brain is a biological masterpiece.
What really happens when we make and store memories has been unravelled in a discovery that surprised even the scientists who made it.The US and Japanese team found that the brain “doubles up” by simultaneously making two memories of events. One is for the here-and-now and the other for a lifetime, they found.
It had been thought that all memories start as a short-term memory and are then slowly converted into a long-term one.
Experts said the findings were surprising, but also beautiful and convincing.
Two parts of the brain are heavily involved in remembering our personal experiences. The hippocampus is the place for short-term memories while the cortex is home to long-term memories. [According to Dan Siegel, ‘long term’ correctly refers to the memories, still in the hippocampus, that last a couple of days. The memories that have been consolidated in the cortex are more correctly called ‘permanent memories’. Ed.]
This idea became famous after the case of Henry Molaison in the 1950s. His hippocampus was damaged during epilepsy surgery and he was no longer able to make new memories, but his ones from before the operation were still there. So the prevailing idea was that memories are formed in the hippocampus and then moved to the cortex where they are “banked”.
The team at the Riken-MIT Center for Neural Circuit Genetics have done something mind-bogglingly advanced to show this is not the case. The experiments had to be performed on mice, but are thought to apply to human brains too. They involved watching specific memories form as a cluster of connected brain cells in reaction to a shock.
Researchers then used light beamed into the brain to control the activity of individual neurons – they could literally switch memories on or off.
The results, published in the journal Science, showed that memories were formed simultaneously in the hippocampus and the cortex. Prof Susumu Tonegawa, the director of the research centre, said: “This was surprising.” He told the BBC News website: “This is contrary to the popular hypothesis that has been held for decades. This is a significant advance compared to previous knowledge, it’s a big shift.”
The mice do not seem to use the cortex’s long-term memory in the first few days after it is formed. They forgot the shock event when scientists turned off the short-term memory in the hippocampus. However, they could then make the mice remember by manually switching the long-term memory on (so it was definitely there). “It is immature or silent for the first several days after formation,” Prof Tonegawa said.
The researchers also showed the long-term memory never matured if the connection between the hippocampus and the cortex was blocked. So there is still a link between the two parts of the brain, with the balance of power shifting from the hippocampus to the cortex over time.
Dr Amy Milton, who researches memory at Cambridge University, described the study as “beautiful, elegant and extremely impressive”. She told the BBC News website: “I’m quite surprised. The idea you need the cortex for memories I’m comfortable with, but the fact it’s so early is a surprise.
This is [just] one study, but I think they’ve got a strong case, I think it’s convincing and I think this will tell us about how memories are stored in humans as well.”
For now, this is simply a piece of fundamental science that explains how our bodies work. But Prof Tonegawa says it may illuminate what goes on in some diseases of memory including dementia. One of his previous studies showed mice with Alzheimer’s were still forming memories but were not able to retrieve them. “Understanding how this happens may be relevant in brain disease patients,” he said.
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