how can our brains remember that we forgot something, but it can’t remember what we forgot?
In: Other
Because “having some information” and “knowing that you have some information” are two entirely different pieces of…erm.. information.
Think of it like pictures on your computer. The content of the picture and the name of the file that contains the picture are two different pieces of information that have to be stored independently by your computer. It is entirely possible to lose content (corrupt the file) while still having its correct filename. In the same way it is possible to mangle the file name but have the content of the file intact.
So fundamentally, you shouldn’t even expect that the brain should necessarily remember them in an all-or-one manner. You can remember one but not the other.
You can also have situations where you are just go to a room and then don’t remember why you went there. In this case, you remember where you had to go, but not why.
Think of it like a spiderweb with a point of convergence removed, but the links still headed in that direction.
You have associated memories that recognize that more information is involved, but cannot recall what the specific point was.
Or, think a desktop shortcut where the original file has been removed. The shortcut knows the file should exist, but its gone.
ELI5 – as my psyche dept head put it:
“The memories in the brain are more like clues than a film or video tape. Your brain uses them to reconstruct your memories.”
So there will come a time when a “clue” is missing because it hasn’t been used in a long time, you’re tired, you went on a bender at da club and the Henny got the better of you etc.
Your brain sees that there was a strong emotion tied to a clue but the rest of the chain is broken so it’s all “STUFF IS MISSING”.
If you are lucky, later another stimuli will re-spark the chain and your brain will make another connection and you will go “AH HA!” and remember.
Lots of half-answers here which sort of just reframe the original question as an analogy.
**To understand this we need to understand how memories work**. They aren’t data files. Memories are (simply) stored in what are called *synapses*. A synapse is a connection between two neurons (brain cells). The synapse is how one cell tells another cell to fire. So if we take a simple example, you smell a delicious pie, the neurons that detect that smell set off a chain of synaptic signals that tell your mouth to start watering.
But what about someone who doesn’t like pie? They smell the same pie but their mouth doesn’t water. It’s because the synaptic pathways get stronger the more they get used, and that process is even faster if there’s dopamine released. Dopamine is the “I want that” chemical that our brain releases, and it’s highly involved in addiction and anticipation.
So, when the pie-lover smells the pie, they “want it”, and dopamine washes over their brain. As they start to eat the pie, their mouth waters, and so the pathway from ‘smell’ to ‘water’ gets stronger. The pie-hater smells the pie, and goes and does something else. There’s no dopamine and no strengthening of pathways.
Okay, so **how does this relate to memories?** Well, memories are basically just more complex versions of that. A certain series of events (a conversation, reading something on reddit, whatever) causes you to think of your Mum, and that primes the synaptic pathways. Maybe you’re looking for her in a crowd, and so you’ve got a clear image of her face in your mind. Maybe you’re about to call her for Mother’s Day, and so you start to remember her phone number. All of these are different synaptic pathways that are able to be activated from the initial prompt of ‘Mum’. It’s because you’ve seen her face so many times, or called her so often that you’re able to recall those exact details. The same pathways that light up when you physically look at her face are being ‘refired’ when you recall her face, because those connections have been strengthened over years.
That’s long term memory. There’s also short term memory, and this is I think what the OP’s referring to. You walk into the garage, you know you came in to look for something, but you have *no idea what.* That’s because the object (or the idea to grab it) was stored in your short term memory. You’re just fixing the shelves in the upstairs bedroom, this isn’t something that you do every day, and so it’s not ‘stored’ in your brain. Instead, it’s in short term memory, which can generally ‘hold’ about 5 or 6 objects at a time (this is why when someone gives you a phone number you have to say it over and over to keep it in your head until you can write it down).
The idea stays in short term memory for as long as you’re thinking about it, but if you stop (let’s say because you notice that the grass is getting long and you should mow it, but it’s also getting late and it’s Mother’s Day and you should call your Mum) then the idea fades. You’ll walk into the garage, because that’s a preplanned set of actions that you do all the time, you brain just set it as ‘fire and forget’, but you won’t be able to remember why you came in, because it hasn’t yet been stored anywhere.
So how do you remember what it was? You retrace your steps! This is because whatever the idea was came to you based on something you saw or thought about. So you walk back upstairs, notice the bookshelf is off-skew, and it comes back to you!
**The bottom line is this**: all memories (muscle memory, explicit memory, smell-associations, etc) are stored in our brains through repeated use. This is called ‘Hebbian Theory’, and often summarised as “neurons that fire together wire together”. It’s probably a simplification, but it’s the foundation of most of our understanding of memory and how the brain organises itself.
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Because storage happens by default, but retrieval is more tricky. It’s in there, but you might not consciously be aware of what ‘it’ is.
Im thinking its kinda like this: when a program knows a file is supposed to be there, yet it cant be found, an error comes back. Us ‘remebering we forgot something’ is the brain recognizing a missing piece, and its error message.
We can think of the brain as a library, with an index and all the books. Sometimes you see an entry on the index but cant find it on the library, then later when searching for something unrelated find the original thing you wanted.
This question asks “how is it possible?” and not “how does it work?”, so I won’t talk about actual brains here. But even very simple information storage and retrieval systems can be constructed so that it’s obvious when information has been lost.
For example, let’s say you have a book with 100 numbered pages in it.
Page 46 might be blanked out. You know that’s an error, since there is no page numbered 46 after page 45, and page 47 doesn’t pick up where 45 left off. Something is missing.
You don’t know what was on page 46, but you can be pretty sure it’s gone.
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