Eli5: Since we can miss-remember the past, how do our brains build these false memories? Sometimes our memories can be completely made up.
In: Biology
Basically, the human brain is a pattern engine. When a memory is fragmented, or incomplete, our brain fills in the gaps with something that makes sense. So. Even if you remember it a certain way, that doesn’t mean it actually happened that way.
This happens for our brains the same it does for hard drives or cassette tapes. The more we access a memory, the more we overwrite the data. For tapes and hard drives this causes the medium to degrade and lose quality eventually wear out but our brains are pretty tough so what happens is as the memory fragments, it is repaired with false information which leaks in filling the gap with other experiences.
Essentially our memories become a huge library of books patched with pieces of other books, and each time we open one we find a missing page or couple of words and then replace them with something similar until the book eventually isn’t the same book.
The problem is that people often think of memory the same way they think of data. That it’s just written down somewhere. And that line of thought makes it very difficult to understand how memories could get messed up in the first place. The trick is, that we don’t store things like a computer might, or a book.
Our brains are awful at storing precise packets of data, which is why it’s a challenge to remember your phone number or whatever. Computers are great at these things, because they just write it down verbatim and that’s that. Our brains don’t do that, they can’t do that. Rather, they store stuff in connections between neurons. If you really want to get an idea on how this works, I’d strongly suggest you just google something like “how do neural networks work” or some such, because, frankly, computer science has this shit figured out much more than neurology does. It’s not perfectly equivalent, but the concepts translate remarkably well.
Anyway, point is, we store things in these connections, via probabilities. And that’s the key ingredient here: probabilities. Memories aren’t stored anywhere, they are constructed on the fly, if you will. When you remember something, you are sort of simulating the event again, only that you do so without the same inputs you had at the actual event. When you remember, you can’t ask your eyes what they see or your ears what they hear, you have to reconstruct these things on the fly, from other loose data you have flying around. And this is done via probabilities, because most of this data just flat out isn’t saved anywhere. At best, it is encoded somewhere in the network that is your brain, and decoding it is rarely perfect.
So, say you remember being in the streets one day and some kind of accident happened. Now, it’s suddenly rather likely that you remember hearing sirens, simply because that’s an association that exists in our heads, between accidents and sirens. Whether they were actually there rarely matters, because we can’t ask our ears, we are asking our probability machine. And probability says: There were probably sirens. And that’s how you construct a false memory.
You are especially likely to misremember things that got filtered out by your brain. For instance, those sirens. Maybe if it had been _you_ who had the accident, you would know for certain whether there were sirens, because it would be relevant information for you in that moment. But as a bystander, your brain might just filter that information out because it’s a given – there’s an accident, therefor there are sirens, therefor we can ignore this input. That kind of deal. Same reason why the majority of people can’t give a worthwhile description of a person they saw so much as 5 seconds ago: They simply didn’t care to record these things. And when you ask them to remember that person, they simulate that encounter in their head. And then it’s all back to probabilities, because the actual information just doesn’t exist. For example, maybe you saw a man. Men are tall, therefor this person was tall. Also, it’s usually men who are bald. So now our subject is bald, because why the hell not. You know? The key is that you are simulating these events in your head, because we have no mechanism of actually saving hard data. And you always simulate with imperfect information because of it. As such, every time you simulate it, the outcome is a bit different. Which you then feed back into it when you remember next time, and poof, game of telephone. Do this enough and you’ll remember an event that never even happened.
Again, we can see these exact things in the neural networks we have been building in the past decade or two. If you want to get a better feeling as to how these networks (including the brain) work, I suggest you look into the artificial variants, as they are much better understood, much simpler, and we can actually run tests on these things, in contrast to the brain, because Geneva convention and what have you 😉 A lot of the insights, from that branch of computer science, translate extremely well to neurology, more so than a lot of people would care to admit. Tends to make people _really_ uncomfortable…
Edit: Triggered someone’s notion of free will again, huh?
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