As I was driving, all of a sudden the name "Holden Caufield" came to my mind. It sounded really familiar. I googled the name and it was the main character in The Catcher in the Rye. The last time I even read that book was in 2005. I had no reason to even remember this book because I thought it was boring.
Within the limbic system the hippocampus and amygdala processes memory. The hippocampus processes declarative memory, the memory recalled in the form of thought. The amygdala processes emotional memory.
hippocampus
Hippocampal integrity plays a crucial role in intact memory functioning. Research has demonstrated that normal hippocampal development continues into early adulthood . Investigators specifically examining the development of the hippocampus have suggested that the hippocampal formation undergoes a steep increase in volume until approximately the second year of life, then the volume slowly increases throughout adolescence. 1
amygdala
...here is extensive evidence that the amygdala is involved in affectively influenced memory. The central hypothesis guiding the research reviewed in this paper is that emotional arousal activates the amygdala and that such activation results in the modulation of memory storage occurring in other brain regions. 2
involuntary memory
Involuntary autobiographical memories are conscious and unintended recollections of personal ex- periences. ...
involuntary retrieval, more fre- quently than word-cued memories, accesses memories of specific episodes and involves more mood impact and bodily reaction to the remembered events...
Using a double-cuing methodology, Chu and Downes (2002) found that memories cued by smells were more vivid and detailed than memories cued by verbal labels and photographs of the sources of the odors. Herz and Schooler (2002) found that odor cues yielded more emo- tional memories than did verbal and visual cues 3
Many cues can trigger involuntary memory. Memories triggered by smell, general evoke a larger emotional response with that memory as opposed to visual or verbal cues.
1. Abnormal Hippocampal Development in Children with Medulloblastoma Treated with Risk-Adapted Irradiation
Bonnie J. Nagela,g, Shawna L. Palmera, Wilburn E. Reddickb,f, John O. Glassb, Kathleen J. Heltonb, Shengjie Wuc, Xiaoping Xiongc, Larry E. Kunb, Amar Gajjard,e and Raymond K. Mulherna
2. Involvement of the amygdala in memory storage: Interaction with other brain systems
James L. McGaugh, Larry Cahill, and Benno Roozendaal
3. Memory & Cognition 2004, 32 (5), 789-803
The episodic nature of involuntary autobiographical memories
DORTHE BERNTSEN and NICOLINE MARIE HALL
University of Aarhus, Aarhus, Denmark
In the human brain, information is not stored like cars in a parking lot, with no relation between them, where you can drive away with one car without touching any of the others, but as knots in a network. Thus, a name is stored with connections reaching out to everything that you felt was connected to that name: the tasty italian cookies you ate while you read the book; the body memory of your leg in plaster; the red horse on the cover; etc.
When you happen upon any of the information that is connected to that name – when you eat the same cookies or see someone with a broken leg –, the name will be activated in your memory. The intensity of the activation and if it reaches your consciousness, depends on the strength and uniqueness of the network connection. The color red will be connected to a lot of things and the activation of this particular know will probably be to weak for this memory to reach your consciousness. But someone mentioning Italian pastries on the radio, or getting a whiff of a similar smell, might bring back the memory of your reading.
To know why you remembered the name Holden Caulfield at that moment, we would need to have more information about you at that moment, and about what you did, thought and felt while you read the book. Obviously there was a cue in the moment of remembrance that was stored with the name at the moment of reading or while you thought about the book after reading it. It could have been something you thought about while you were driving and totally unrelated to the actual driving; it could have been a feature you saw (heard or smelled) outside the car; it could have been something on the radio or something your passengers said.
Examples: Someone on the radio says "I'm forever beholden to you." You don't actively listen, but the word is processed subconsciously. Or: You thought about how boring the book was while eating an apple; now you eat an apple and think about how boring the drive is.
Since we do not have that information, all that we can say is that the same cue appeared in both situations.
That you remembered something you had not thought of for eight years does not prove anything about how much information your memory holds. It just proves that the book impressed you in some way – enough to remember the name of the protagonist. Which is why I voted to undo Taal's edit of your question, in which he deleted your characterisation of the book as "strange": "I had no reason to even remember this book because I thought it was boring. It was strange." If you find something strange, then it is out of the ordinary. It intrigues you. And you remember it. Quite simple, actually. (Please undo your edit, Taal.)
I just wanted to add to the current answers, that this idea of one element of a network results in the entire network becoming active (aka a smell triggers the memory) is thought of as a Hebbian cell assembly. Donald Hebb introduced the idea of "neurons that fire together, wire together". And with that in becomes easier to think of how one spark (for whatever reason that may be) will activate the whole network, or only the strongest parts.
Nearly everything that goes on in our minds happens "for no apparent reason" because we are only conscious of a small part of our mental activity. If it were not so, we would have too much to attend to, and could not think rationally. "Life without filters would be overwhelming."
It has been shown in the split brain research that we can have two entire separate consciousnesses in one brain (if the corpus callosum is severed), and it is easily possible to have many unrelated "bubbles" of awareness / mental activity going on at once.
One time, when I was about to get in to a boating accident (I narrowly missed hitting a piling at night) I had 4 separate conscious thoughts speak in my mind at one time, while I was trying to see ahead AND my body was turning the wheel so hard that the boat went up on its side. I reacted before I could see what I was going to hit, and had thoughts about the outcome and other things going on (a huge meteor went across low in the sky right in front of me right then) before I had even averted the collision.
The wonder is that we spend so much time "alone in our heads without adult supervision" that we are not more aware of the many levels of simultaneous perception, memory, reaction, deciding and responding which go on all the time. But it is Ego which suppresses all of that, in favor of narrating life to itself. I am not surprised at all when some lower-priority thought interrupts with something important, interesting, relevant or just unfathomable to my pitiful self-awareness at that moment.
Do we "remember everything"? No, I don't think so, but there is a lot more in memory than we are aware of. Salient things come back to our recall. I had a dream once of being in a house, and I held on to many details of the dream when I woke up. I wondered if it was the house my family moved out of when I was 3, which I have no significant memories of. I described what I had seen in the dream to my parents (I was about 45 at the time) and they confirmed that it accurately described the house. So, the memory was there, I just didn't have a consciously available 'handle' to retrieve it. Dreaming brings up many things that do not arise in waking consciousness.
