Aging Brains Blend Memories Together Instead of Just Forgetting Them

I wonder how much of this is directly related to age (biological aging), and how much is just someone's brain becoming "full" due to more memories getting added every year?

It seems that memories must be stored as embeddings with single multi-neuron assemblies (cortical columns?) storing multiple embeddings as a kind of contents-addressable memory that is able to keep memories distinct due to the very high dimensional space (# neurons per assembly) being used. However, you'd expect that at some point if you store too many memories in a single assembly the recall accuracy is going to go down.

You'd expect that with big brains being so costly, evolution has only equipped us with brains big enough to store a lifetime of memories, so it would be odd if memory didn't suffer as we get old.

To make a computer analogy, it's a bit like a hash table getting too full. Say you had a hash table without any overflow mechanism... up to a point recall may still be pretty good, but as the table gets closer to full there will be more hash collisions and likelyhood of "false recall". Obviously the brain is not a computer, but the analogy may hold up reasonably well if you consider the hash table keys and values as embeddings and the store operation being an embedding merge rather than overwrite.

Gonna chuck a thought for you all. In social situations there is someone who talks alot and I think they are able to do so because they have lots of stories they can recall in good detail (maybe not perfect) but 20 year old event they are describing better than I can describe last week. Now I assume they don't have that rare calendar level memory but they do have a huge storage of stories and events. I am pretty jealous tbh!

Also that skill is probably excellent for interviews which is the ultimate memory test. I.e. Tell me a time when you turned water to wine, plus 5 deeper questions, any hesitation will be chalked ip as suspicious AI use.

For me I either do or I remember which makes performance management and interviews hard for me (as someone vouching for someone as evidence is rare now).

The paper certainly has its limitations. Only 61 participants, with almost nobody between 30 and 50, so we shouldn’t read the age trend as a decline across lifespan. What’s more interesting than the title suggests (and I find the title forcing the conclusion a bit) is that the attention measures were not linked to age or the brain patterns at all.

Then again, i'm 45 and I've been losing my keys and my IDs since I was 20

The concept of memories blending together resonates after watching a recent Kurzgezadt video entitled "How Are Memories Stored Inside Your Brain?". It makes the point that the very act of recalling a memory changes it:

https://www.youtube.com/watch?v=PqtggjVAi8M

> But memories are not static like photos. Like dioramas made from wax, each time they’re under the spotlight of your attention they can melt and change a tiny bit.

My theory behind this is that when you encounter something new/novel it is distinct enough to remember -- where you were when you learned of 9/11; the days around the start of covid/lockdowns; being in a car accident; getting married; etc..

However, when you experience the same thing repetitively -- having breakfast; getting ready for school/work/etc. -- it doesn't make sense for your brain to remember each of these events as distinct events but to mush them together into a single or combined memory. This may be due to how the brain indexes/references memories and that memories with the same references get combined together.

This is also partly why time appears to go faster when you get older -- the same day-to-day events blend together but the key milestones (holidays, etc.) stick out.

Compacting

———-~~~~~~~ 40%

This comes as absolutely no surprise to me -- my mother was recently transferred into memory care, and the changes to her memories are definitely showing some interesting changes. The foremost was that her new "apartment" is shared with one other person, gives off a bit of a dorm room vibe. First day, she was talking about how excited she was to be going back to school and seeing her boyfriends again(?!). I said, "Oh, like Doug? [my dad]". Her response? "Ew. No."

But, she's come around on that, and recently been upset about the affair he's been having (they divorced in 1980), and is irate over him having another kid with his new wife (1983), but isn't surprised that I haven't spoken to him in 12 years. She's never surprised at how I've aged, but doesn't remember her grandkids even exist and insists on meeting them soon (but remembers them when she sees them). Two weeks ago, she called to yell at me for things I did in high school (1990). At this point, I seem to be the anchor for everything recent, but when I'm not around physically, it's scattered everywhere else.