At times, apparently mundane memories are really easy to recall, and moments you think ‘I want to remember this in detail, even gonna do an eye-camera pan of the scene’ don’t come back that easy. Why?
In: Biology
The actual mechanics of memory formation aren’t really being mentioned so far, which surprises me. I highly recommend some popular neuroscience like Steven Pinker for a deeper dive on this subject, but here’s a what-I-remember gist: memories and other mental structure are formed by groups of neurons that ‘learn’ to fire in a certain way through repetitive use, like a line on an etch-a-sketch that won’t erase any more. The beauty of the brain is that one bit of circuitry can be part of many different total pathways and it’s all kind of modular and interconnected, but the important thing here is that neurons are plastic, they can reset and be reused like the grains in an etch-a-sketch, and when you think or experience something trivial they very quickly stop firing in the pattern it stimulated and are ready to be repurposed. This is why you can forget something after 30 seconds, and why your head isn’t full of literally decades of minutiae. To only keep the good stuff, the higher order ‘software’ of your brain has systems that rank and prioritize experiences and thoughts, and ones that meet its criteria are reinforced by repetition.
This reinforcement is key, and you’ll sometimes be aware of it happening. Read something once and never think about it again, and you’ll definitely forget it. What do you do if you really need to remember, say, a license plate or phone number? Keep saying it to yourself. It works: as the pathways are repeatedly fired, the groups of neurons corresponding to that thought get trained, and fire in that pattern more readily when stimulated again in the future. A memory is formed. It’s also associative, as one ‘group’ or ‘pattern’ can trigger another, hence always thinking of the same movie quote or song when you pick up a particular object or visit a particular place. These links can be arbitrary to begin with, like thinking “toothbrush – bat cleaning meme – bats – Batman” but if you think it enough times, it becomes permanent, and suddenly toothbrush = Batman forever, however hard you try to dissociate it.
Side note: this is why we should take trauma and PTSD more seriously than we naturally might – it isn’t just trauma victims ‘getting their feelings hurt’, it’s more physical and deep than that – stimuli can set off these associations and then they’re actually having a flashback, their brain reliving a horrific memory in detail, firing all the corresponding neuron groups at once, freaking them out. It’s a different kind of remembering to when you try to remember the colour of a car you once owned.
Which brings us to the other side of it, and your question. If memories are formed by repetitive stimulation of groups, like reciting a license plate, why do we spontaneously remember some things without trying to, like trauma? To say they “make an impression” is kind of circular, but accurate. Impressive experiences or ideas get obsessed over by your mind, consciously or otherwise. Against your will, your mind simply decides that the thought is important, and recites it. These subroutines come to the fore when your brain is unoccupied, which I believe is why you sit at 2am suddenly thinking about unresolved traumatic or disturbing things in your past. Your mind is still quietly obsessing over them, rewriting them more and more deeply into your brain. I presume this is how we get to having neuroses and anxiety: circular thought patterns that happen too easily precisely because they have been trodden many, many times. (This may also weigh into the culture war arguments about microaggressions: in neurological terms, a small repeated stimulus really does have a larger impact than the sum of its parts, but I’m unqualified to comment further.)
Why does your mind do this automatic memorizing and obsessing? Since the mind and brain have been meticulously crafted by natural selection, the answer is fairly obvious: it confers a survival advantage. The tribesman who narrowly avoids getting mauled by a tiger and then spends weeks subconsciously obsessing over it, memorizing and internalizing the experience, is more ready to react and run next time than the tribesman who happily forgets about it and sleeps peacefully, never giving it a second thought. This is why we shouldn’t be too angry at our minds for having this obsessive quality: it keeps us safe and makes us remember things likely to make us feel strong positive and negative emotions, which in turn makes us more equipped to seek and avoid them in the future, improving our odds of happiness. Even if it does sometimes overshoot and leave us sitting up at night, worrying about someone who bullied us 20 years ago.
Postscript: the missing detail in my reading so far is which triggers set off this process of prioritization. What makes your mind choose certain things for reinforcement? How does it know a tiger attack is more noteworthy than a stroll on the beach, and why do random things sometimes meet the criteria? I suspect it involves emotion. The stronger the cocktail of emotions stimulated, the more it ranks. But that is only a guess, maybe others can expand.
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