How does the brain know which memories to keep and which ones to delete?



Like, I can remember that I spilled orange juice in the living room when I was 5, but can’t remember what I had for dinner last Tuesday.

In: Biology

I don’t know much neurology/psychology, but your example made me think of the amygdala. The amygdala is a part of your brain that is involved in memory, but also fear and emotion.
As far as I know it highlights highly emotional memories (especially with negative emotions), which makes sense as those are the things that we should avoid repeating unnecessarily.

You spilling juice would probably stress you out as a kid, being afraid of your parents reaction, being overwhelmed with the situation and maybe guilt for spilling the juice/spoiling the carpet/…
Dinner however is not particularly important or interesting.

Memories that aren’t accessed very frequently or for a very long time tend to be the first to go.

Other than that, it’s typically not a failure in “remembering” as it is a failure in writing or storing information. Eating dinner is such a mundane and boring event that we often just don’t even bother to write/store the exact details of it, while spilling orange juice is something that stands out as a unique event.

You can think of memories as little towns in your brain. When you have an experience it’s like settling a new little town in your brain. If the experience is significant the town will be large and if it’s small the town will be small.

Now when you have those experiences again, more people move into that town and it gets bigger. They build bigger roads and make it easier for people in that town to tell you about that experience. Even small towns can get quite large if it is an event which happens often as each time it happens, more people move into that little town and make those roads stronger. The little towns never leave either they are always there but it will be very difficult to communicate with that town (making it difficult to recall that experience)