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Does a person's brain have a record of every event that happened during a person's lifetime? Is it possible to recall any of those events and is it possible to recall those events in detail?

For example, I almost drowned when I was a child. I know this happened and can remember bits of the event but I don't remember all the details. Is that complete memory still stored?

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No. Not for hardly anyone, because cells and synapses die. –  user3153 Jun 19 '13 at 0:17
    
Do note that 'the complete memory' is a very dangerous term; the act of remembering often creates details that didn't exist in memory by simply making them up, and this process is very open to suggestion from outside sources. Furthermore, if you think about these details, they will get stored in memory, and it may be impossible to ever find out if those details were in the original event, or you imagined/'remembered' them afterwards, they'll feel exactly as real. –  Peteris Feb 24 at 10:17

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No. I don't think so. There are many arguments for why this is not the case.

  • A common understanding of human memory is that it is part of an information processing system: attention, sensation, perception, interpretation, memory consolidation, forgetting, and memory recall. In some sense all these represent possible points of failure. Thus, we can fail to attend to an event in the first place, we can misunderstand the nature of an event, or memories can be temporarily inaccessible.
  • Building on the idea of the information processing system, it is important to recognise the huge subjective component to the experience of an "event". This links closely with philosophical questions about the nature of reality. However, regardless of the nature of the truth of external reality, it is clear that human experience is imbued with meaning and is experienced through various cognitive schemas. Thus, the "objective event", whatever that might be, is often never represented in the first place.
  • Another perspective is that memory has been shaped by the adaptive needs of humans. In such a context, memory consumes resources. Memory also needs to efficiently serve our needs. From such a perspective forgetting of irrelevant memories and consolidation of life saving and life improving memories is important to our adaptation. For example, this is an argument for the benefits of a forgetting curve whereby recent memories are recalled better than distal memories; recent memories are more likely to be relevant to current behaviour.
  • There is so much research to show the failures of human memory in even short term contexts. For example, check out some of the eye witness testimony research of Elizabeth Loftus to see how poor people are at recalling details even short term. The entire field of memory research extensively documents failure of recall and biases in recall.

Despite all this, there are also many times where people can not currently recall something that is stored in long term memory. See for example discussions of tip of the tongue phenomena, spreading activation, fan out effect and so on.

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I'm flagging this for no references and reporting you to a moderator immediately. ;) –  Chuck Sherrington Jun 20 '13 at 8:41
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@chuck I want to make a comment about the irony in your comment potentially giving rise to a flag, but I worry that the irony in my comment might also be flagged. –  Jeromy Anglim Jun 20 '13 at 9:29

There are individuals who possess extraordinary memory ability, sometimes called eidetic memory. With specific reference to your question, a woman in Los Angeles has an extraordinary ability to recall autobiographical events from her past. You can read the Wired article of her story here.

At the scientists' behest, for example, she recalled—without warning and in just 10 minutes—what she'd done on every Easter since 1980. "April 6, 1980: 9th grade, Easter vacation ends. April 19, 1981: 10th grade, new boyfriend, H. April 11, 1982: 11th grade, grandparents visiting for Passover ..."

Her ability extends to certain momentous cultural events, such as disasters.

She instantly retrieves from memory the exact dates of the explosions of space shuttle Challenger and Pan Am flight 103 over Lockerbie, Scotland. She remembers not just that September 25, 1978, was when a PSA flight crashed in San Diego but also that the jet collided with a Cessna. She can go in either direction, disaster to date or date to disaster. When I say "January 13, 1982," Price has no trouble recalling the Air Florida flight that plummeted into the Potomac.

One theory of her astounding memory is that she obsessively thinks about events after they happen, which leads to more effective encoding and strengthening of the memory for that event. This seems to be a key distinction between her and a person of average memory - if you didn't encode an event completely when it happened you are unlikely to be able to recall it completely later. Trauma, such as nearly drowning, can either enhance or degrade this process.

If you are curious, a great book that goes over our many memory failings is "The Seven Sins of Memory" by Daniel Schacter. Highly recommended.

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(1) There are different kinds of memory:

  • a "sensory" (e.g. visual) memory of events as they happened
  • a verbal memory, i.e. the knowledge that something has happened (verbalization being the result of higher cognitive processing or "reflection")
  • a behavioral memory, i.e. a specific reaction to certain stimuli that does not appear in individuals that did not experience the relevant trauma

The purposes of memory are correct and efficient future behavior. A detailed sensoric memory is not helpful in achieving these purposes, so it is usually not retained.

Verbal encoding becomes more likely in older children (older than 28 to 36 months) and is better in girls. Children of all ages preserve a behavioral memory. (Terr, 1988)

(2) Traumatic and negative life events are less well remembered than positive life events (Byrne, Hyman & Scott, 2001), and it seems that memory is correlated to the type of trauma. In one study (Williams, 1994), 38% of abused women had no memory of that (documented) abuse. Forgetting the abuse was more likely, if the perpretrator was part of the girls family. I would interpret this as the trauma being more severe, if the child's trust was broken. Forgetting this may be a coping strategy (see 3, below).

(3) Forgetting of traumatic events seems, in part, to be due to these traumatic events to "fall out of" and "not fit into" the individuals world view (Janoff-Bulman, 1989). Whenever we experience something new, we have to either adapt our idea of the world to include this new experience, or we can, among other strategies, deny, ignore, or simply forget, that it happened. In the case of childhood abuse by close relatives, accepting the event as a fact, would result in the child loosing its family and all trust in the world. It would be unable to survive. Forgetting the trauma maintains a world that can be lived in. Deliberate forgetting can be found in victims of genocide (Buckley-Zistel, 2006). Forgetting can be willfully induced (Joslyn & Oakes, 2005).

There's a wealth of research into forgetting of traumatic life events.

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