Biology Magazine

Brain Full of Memories

Posted on the 31 January 2011 by Realizingresonance @RealizResonance


I have always thought that I had a particularly good memory, both for retaining knowledge, valuable and useless alike, and for the various experiences in my life, both dramatic and mundane. So many events in my life have been dramatic, and make for such interesting stories, that I often worry that divulging too many of them to a new acquaintance will surely finger me as a habitual spinner of tall tales. After only living for about a third of a century I can remember: being on the news three times; partying in New Orleans for Mardi Gras; partying in Las Vegas for the Y2K New Years celebration; following the Backstreet Boys on stage to play guitar in front of a huge audience at the Tacoma Dome; travelling through Europe and Peru; and several incidences of narrowly escaping horrible injury or death at the hands of fire. I have even written an essay about that last collection of memories due to the un-believability of just one them, let alone a whole matching set. I also feel like I am quite good at recalling mundane events from my life, and acquiring knowledge about subjects I am interested in like music, philosophy, maps, history, computer programming, and much more. What makes me good at memory retention and recall, and where might the confidence in my abilities be misplaced? In his book, Searching for Memory, Daniel Schacter elucidates the enigma of past recollection and explains its power and the reasons for its failure.

Most people are aware of the distinction between long term and short term memory. However, the process of memory is composed of several interdependent functions so that these broad categories can be further subdivided. Short term memory is also known as working memory, and is used for keeping information in the conscious mind for immediate use. Working memory is also the starting point for recording experiences into long term memory. One aspect of working memory identified by Schacter (43) is the “phonological loop”, which is utilized when you repeat a short piece of information over and over again in your head to keep it in mind, like a phone number. The phonological loop is just a small portion of working memory, which is defined as any newly acquired knowledge that can be recalled after short delays. This data can be superficially encoded, like with a phone number we forget the second we finish dialing it, or elaborately encoded, which allows the information to be stored in our minds more securely for the longer term.

Long term memories come in three distinct flavors, semantic, episodic, and procedural. Semantic memory is the ability to recall facts and knowledge, like the names of people, objects, and concepts, along with their relationships. For example, if you ask me about a particular Iron Maiden song, I can tell you the album it was released on, the year it came out, and which members the band was composed of at the time. Episodic memory is the ability to recall specific events and autobiographical knowledge. In March of 2008 I travelled to New York to see Iron Maiden live for the first time, and I can remember walking through the Museum of Natural History when a man visiting from Bogota, Columbia stopped me to ask about the concert because he saw that I was wearing the band’s t-shirt. We were standing right next to the giant skeleton of a Triceratops. Procedural memory is the ability to recall physical skills, or to conduct habitual tasks. My aptitude for playing guitar is an example of a procedural memory, especially when I just let my fingers fly across the fret-board, soloing unconsciously. I know this even improvisation is a learned skill, because I can only improvise extensively in the key of A-minor, since this is the only scale on the fret-board I ever memorized.

When memories are recalled there is a difference between actually remembering something and just knowing it. Schacter characterizes these memories as explicit and implicit respectively. The key difference in these types of recall is that with the explicit version, a source memory is attached, while with the implicit version, the source of the knowledge is forgotten. For example, I remember that I first learned that my ancestor John Endecott was the first Governor of Massachusetts Bay Colony when my father mailed me my family tree about five years ago. This is an explicit memory. On the other hand, I know that my father served in Vietnam as a trombone player for the Army band, but I could not tell you when I first learned this information. This is an implicit memory. Schacter has described a technique called priming that demonstrates that semantic and procedural memory can be learned implicitly in people with amnesia, even if they cannot explicitly remember acquiring this knowledge. There is also a difference between free recall and recognition. Free recall is the ability to search the mind for a needed memory, while recognition happens when that memory is called to consciousness by a particular cue.

How then are memories formed, and why do some become stronger than others? First of all, memories have to make it into long term storage to begin with, and this relates back to the type of encoding we use, whether superficial or elaborate. Just repeating a string of words or numbers in your head will not be enough to permanently retain them. However, by elaborating on a piece of incoming information by connecting it to other facts already known, we can greatly improve our chances of remembering it later. I have spent a long time trying to memorize all of the US Presidents in order, and it took learning the historical context of their respective terms before I could successfully recall who served after whom. I can remember that John Tyler came after William Henry Harrison, because of the old campaign slogan, “Old Tippecanoe and Tyler too.” Repetition of new information is also very helpful. For example, I am best at retaining the various political, philosophical, and economic data that I learn through my college studies by relaying what I discover to others. If I am grappling with a particularly difficult set of concepts to digest I try to, in essence, teach these facts to as many other people as I can.

Some memories are impossible to forget. Highly emotional states can burn images into our brains, making recall easy and sometimes overwhelming. Schacter discusses flashbulb memories, or our ability to easily retrieve details regarding the circumstances in which we learn about a shocking piece of news. The assassination of JFK is typical example of this. Just the other day my father was reminiscing about how JFK was killed four days before his sixteenth birthday, and he remembers putting off his driver’s test for weeks after that because it no longer seemed important to him. September 11th was the perennial flashbulb moment for my generation, and I remember being at work and hearing about the first plane hitting the World Trade Center from a customer I was helping over the phone. After ending the call I watched the ongoing attacks unfold on TV in the break room, with a crowd of my fellow co-workers. Also, traumatic and highly emotional incidents can be burned into our memories. My father, like so many other veterans, has suffered from Post Traumatic Stress Disorder (PTSD) following his tour in Vietnam, where emotionally stressful situations were common. Overwhelmingly good feelings can deeply encode memories as well. I know I will never forget the details of proposing to my wife at Machu Picchu, performing in front of thousands of screaming fans at the Tacoma Dome, my wedding, or my honeymoon cruise through the Mediterranean, because they were just too wonderful. Intense emotions, whether good or bad, will greatly influence our ability to remember the events of our lives.

The ways in which we retrieve memories are just as important as the ways we encode them. The way we perceive the past is always tinted by features of the present. This merging of previous and current experiences into related layers of occurrences has implications for how accurately we recall them. For example, it is much more difficult for me to recall what I had for dinner three weeks ago than it is to remember what I ate the night my wife and I had an especially romantic dinner on our honeymoon cruise. This is because the latter was a unique experience, while my typical dinners have so many common features that they all blur together, and these events tend to overwrite each other in my mind. We can strengthen a memory by recalling it often, but each time that we do we make new associations with the circumstances we are in when recollecting. I have travelled to Barcelona twice now, including my recent honeymoon, and my current mental picture of this splendid city is much more in tune with my recent trip than my first visit. The associations we form when encoding memories also act as cues for their recall. I often cause old forgotten memories to spring to the surface by listening to songs I associate with those moments in time. Just one old song can flash me back through chains of recollected moments. Having discovered this trick early on, I use different pieces of music, in conjunction to the location I lived in, to determine the likely time frame for most of my memories.

However powerful human remembering is, it can also be extremely fragile. Alzheimer’s disease and Amnesia are tragic situations in which memories are unreachable, and people can virtually lose their complete sense of self when they cannot recollect even their names and personal history. In 2009 a man wandered out of Discovery Park in Seattle with no memory of whom he was and why he was there. The man was confused and frightened by his inability to recall his name or when he was born. Despite not knowing most of his autobiographical past, he was still fluent in English, French, and German, had a professorial knowledge of European cultural history, and believed he had travelled the world (Ith, Welch). Retrograde amnesia like this, as well as other types of memory disorders can result from physical injury or deterioration of the specific brain regions needed for retention and recall. In the previous example that man appears to be able to form new memories, but people can also suffer from anterograde amnesia in which they can no longer form new memories.

Aging in general causes the ability to remember recent experiences to decline, and elders have a much easier time retelling stories from their distant past that they have rehearsed many times before. For example, my grandfather was able to give such detailed descriptions of his World War II experiences that my aunt transcribed and saved them for future generations. Of course, my grandfather told me the some of the same stories multiple times, apparently forgetting that I had heard them before (I’m told I do this too). I never reminded him of this though, because the tales were so interesting and I could tell he really enjoyed telling them.

It is common knowledge that the brain is the primary organ for memory storage and retrieval. However, individual memories, or engrams, are not just stored in discrete locations in the brain, but dispersed among specialized regions connected by networks of neurons. The neurotransmitter dopamine and its receptors play an instrumental role in memory formation in the brain, aiding the determination of the relative strength or different memories. Working memory, semantic memory and priming, and procedural memory rely on the frontal lobes. Ongoing day to day memory of recent events requires the hippocampus, and the emotional elements of memories are supplied by the amygdale. The left interior of the prefrontal cortex aids in the elaborate encoding of memories. The networks of neurons connecting these areas actually create the engrams that we perceive as discrete memories.

Whenever we encode information into memory, the process can cause distortions in the events. Pre-existing knowledge tints the way we see the world and how we view ongoing events, which can cause us to remember them differently than they actually happened. The conditions under which we recall past experiences can cause distortions in those memories as well. Psychoanalysis and hypnosis are the most extreme methods for distorting recall, especially when the memories recovered are of past lives and alien abductions. Pseudo-memories are the recollections of events that never took place or happened to someone different than the person remembering. False memories can occur if the source of the information is forgotten, causing a person to confabulate an implicit memory by filling in missing details with a subjective view that distorts it into an explicit, although pseudo-memory.

Schacter discusses the controversy surrounding the idea of recovered memories. He argues that traumatic events can overwhelm us and we may repress these memories psychologically. This is called psychogenic amnesia. However, hypnosis and other types of regression therapy, has pulled to the surface many apparent memories of repeated sexual abuse and the even more spectacular claims of satanic rituals. Schacter argues that while people can suffer from pathology that causes them to blackout a particularly disturbing event, our understanding of how memory works contradicts the more extraordinary claims of repeated incidents of abuse being repressed. That is because repetition of similar incidents has the effect of strengthening recall for the congruent details of these events. We can use Inference to the Best Explanation to determine the quality of evidence that Schacter (273) puts forward to discredit the veracity of recovered memories:

E1: Documentation of experiments where memory has been shaped by suggestion under therapy. E2: Under hypnosis people have created inaccurate pseudo-memories that they truly believe. E3: Evidence of satanic rituals has never been discovered in extensive investigation. E4: People have recovered memories from past lives and alien abductions under regression therapy. E5: Many people with recovered memories have retracted and no longer believe they are true. E6: Strong emotions tied to imagining can construct strong implicit yet illusory memories. E7: Risky techniques like using guided images for deep probing under hypnosis are often used. ======================================================== T0: At least some recovered memories we induced by therapists and did not actually happen.

Schacter’s conclusion concedes the possibility the many recovered memories are real, but he urges caution on risky techniques. He suggests that we not act solely from recovered memories alone if other evidence does not corroborate the images like past expression of the behavioral symptoms of repression. The extreme alternative to Schacter’s position is that all recovered memories are essentially true. With only a basic understanding of how memory works, this rival appears absurd. Therefore we should expect that at least some recovered memories are in fact false, especially the accounts of ritualistic satanic abuse and alien abductions. Obviously most of our regular memories can still be trusted, and the ability to suddenly recall long forgotten events with a peculiar cue should not be suspect. I will enjoy telling stories about my experiences to future generations of Endicott’s, and I am not going to worry too much about whether some exaggerations have distorted them slightly over the years.

Jared Roy Endicott

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