@monolyth  

 
Uh…what?

Disingenuous equines with their subliminal chicanery - a pox on them!

Translation: it makes my talking sound pretty

Pure, epic win this.

@when she felt her wings unfold  
I didn’t really mean to say that no compression occurred, but the it’s certainly not doing so into a format that allows us to compare it to how much digitally compressed video could fit in a terabyte of the like. For that matter even the answer to that later question depends entirely on what level and type of compression is being used. You’ll fit a shit ton longer 480p video into that terabyte when you will 1080p.
 
Maybe I wasn’t clear, but my overall point was that you can’t really compare the brain to a hard drive that can store X years of media. At least not at this time due to our limited understanding of the ‘device’ and how it actually stores information.
 
As for the other bits that’s pretty much what I said things that are important and have impact would be retained more. Perhaps virtually indefinitely so long as they were recalled often enough so the brain knew to prioritize them, but those memories would likely blur regardless cause it’s not like you could spend all your time thinking about all the aspects of and experiences with things you’d known over the years, not with new things constantly vying for space. If they were important perhaps you’d retain an image of them, their name, overall personality or purpose, but would you recall specifics? If someone asked could you recount some funny little anecdote about a person from a thousand years ago or explain how exactly some long lost arcane item worked?
 
And then if you lived a really long times perhaps at some point you’d reach an age where even that wasn’t enough and you’d start forgetting ‘important’ things altogether because there were just too many important events to recall them all. That would probably be rather tragic to perhaps come across some record or the like that talks about how important so and so was and how much time you spent with them and then find yourself unable to recall you ever even knew them within in your own memory.
 
If that’s even worse or in someways a bit of a mercy for an immortal is probably a matter of opinion. It might perhaps be both at different times to the being in question. As it starts to occur it might be treated almost like the onset of Alzheimers and met with desperate attempts not to lose things, but as the same being became truly ancient it might come to view it as a blessing. That the loss of older information allows for endlessly ‘new’ experiences and reduces the burden of the ages.
 
It might well come to be regarded as almost a pseudo-reincarnation. After all from a philosophical point of view if all the memories and feelings that composed a being at some given point in time are eventually overwritten and lost, is the being from that point in time really ‘alive’ anymore once that occurs? The body remains, but one might say that the ‘soul’ of that particular incarnation is gone.

@Mad Black  
Scrabble is Parker Bros, a subsidary of Hasbro nowadays.

@when she felt her wings unfold  
Scrabble is from hasbro?

@when she felt her wings unfold  
Hasbroception?

Also, Hasbro products playing with Hasbro products again. How come that’s not some kind of tag already?

@Tk3997  
Kinda right, but sensory processing chains do compress. Just not in any neat digital format which would allow the original signal to be reconstructed. For visual processing, it happens for bandwidth reasons: the retinal nerve can’t transmit anything like an RGB TV signal, and the visual cortex couldn’t process that mass of undifferentiated data, so things get segmented and simplified in stages along the way. So you get more of the signal devoted to edges of objects and areas, say, and less to the contents of those blobs. Colour is processed by different chains of neurons to brightness-vs-darkness information, and gets less resolution and thus bandwidth devoted to it. Hearing, smell, touch, proprioception, taste, heat, pain senses probably have similar evolved (and thus messy) optimizations, and it’s the job of the brain and memory to (re)associate all of this fragmentary crap and try and make some subjective sense of it to itself. But if that’s all it has to play with, that’s what is “stored” as memory (abstract concepts aside)
 
And it does a lot of that storage and recall by salience - how emotionally charged a memory is when it’s formed, for example, or how subjectively important it seems to our biased, monkey instinctual side. The more salient something is, the stronger the neural connections laid down, and the quicker and stronger the recall later on. Another evolutionary optimization of course, because it’s beneficial for individuals to be able to recall Important Facts About Leopards really quickly in leopard-filled emergency situations. Helpfully we tell each other (scary) stories about such things, but that counts as learning too.
 
So basically I like the idea that Best Princess and Celestia have an antidote to the immortality blues though gradual loss and replacement of memory. That would be a kindness, but sadly not all memories are lost at the same rate. The more important and emotionally charged a memory was, and how often it was remembered, the stronger and less likely to be forgotten it would be. A great many losses of loved ones, sure, but the more important a pony was to them the more painful and less indelible the memory - especially when you consider that they’d be revisiting writings, artefacts and possessions essentially all the time for the truest of family and lovers and friends.
 
Which sort of makes even it more tragic.
 
(But I wonder - how much would such a revisited memory change and drift over time even in a brain which effectively doesn’t age? If such a person were to walk though a portal and say “hi”, would you even recognise them?)

@Mad Black  
The brain isn’t a tape recorder. It would be so much simpler if it was, but it’s not.
 
Just for a start it has to record taste, sensation, and smells as well. How much space do those take up? If you know there are a number of neuroscientists I bet would be eager to talk to you. For that matter how much space does visual or audio memory take up? We don’t really know that either, and it seems rather unlikely your brain is compressing visual input in MP4 format to allow a convenient comparison.
 
We can’t even really say for certain how information is spread out and stored within it, or even what cells really do what related to memories. So any estimate of ‘total size’ is extremely suspect, as even the people guessing at it admit. This is why you get ranges from as low as 1 TB to 2.5 Petabytes from well educated people. The assumptions they plug in at the front totally alter what comes out at the back. Beyond that these numbers are comparatively worthless anyway since as noted we also have no real idea how much space a given sort of memory even uses so have no real clue how much you can fit in that supposed space.
 
In the face of such comparatively useless science it’s probably best to consider this question based on observational data or people and our own experiences with memory, and in humans at least neither inspires very much confidence at all that you’d recall shit if you lived a thousand years.
 
Think hard and honestly about what you were doing ten years ago, do you truly recall much besides broad strokes interspersed with more concise recollections of certain key events? Unlikely, this sort of thing is why we write things down. Indeed some people have compared advancing recording technology to a kind of ‘external cybernetics’ a technological aid that improves our sketchy biological storage.
 
Then again the princess are of course out and out magical which I could provide handwave for this, but I kind of like the idea that they’re not immune to it. It would be a fun take for a response to the cliche “how do you deal with living so long” question to get an answer like.
 
“Well it’s not like I really recall much of anything from a thousand years ago. Honestly it’s all a total haze outside a handful of still rather blurry recollections. If I want to recall something more then maybe a century or two back I have to go read a book like anyone else, and you’d be better of reading one two then asking me about it.”

@Tk3997  
Well you have to consider that the human brain has between 1 TB and 100TB capacity.
 

 
[source]
 
Some even say 2.5 petabytes. Which would be an equal data of 300 years of TV run time.  
So yes, theoretically a being, which is 1000 years old, should be able to remember a lot of things.

@Starlight Storm  
Being immortal =/= perfect recall.
 
I’ve always found it somewhat funny how these two often seem to be assumed to go hand and hand. It often seems just taken for granted that some long lived being should somehow recall in great detail crap that happened a thousand years ago, but if you stop to consider that actually doesn’t make a ton of sense. If the longevity is biological the brain, even with perfect health, has a finite storage capacity.
 
In order to keep making new memories you would have to keep deleting old ones. After a few centuries it would be likely that you’d recall only the most life altering and defining moments from earlier in your life. Which could be a good or bad thing depending on how you look at it, I suppose. Trivia like obscure words that are no longer used is probably not the sort of information that’s retained.

well I had to look up learned at least four words because of this one page.

Vernacular? Dat’s a doiby!
 
Nyuk nyuk!

@James Rye
 
Vernacular: Language of the people.
 
It is a fancy was of saying ‘common speech’.
 
-Lumino

What’s vernacular and why can it be pleasant?

@BigMax  
I give you that, and maybe that’s a valid excuse. Still, I think they make Luna sometimes a little too shallow headed.

@Starlight Storm  
Maybe Star Swirl invented the aetheneum and then the term was popularized after Luna was banished.  
Keep in mind that I’m not serious at all about this, since it’s just reading too much into a comic to me.

@BigMax  
Starswirl already had his library/aethenaeums before Luna was banished. In the flashback Celestia and him are talking about how she’s becoming distant and dark.

@Starlight Storm  
Maybe aethenaeums weren’t invented yet when she was banned to the Moon.

@Vree  
SO in character for Spike, but also SO out of character for Luna. Remember in Luna Eclipsed how she only spoke in Old Medieval-ish terms? How in the world does a princess supposed to be more than a thousand years old don’t know the old word uses to reffer to a library?!

This.  
Is.  
GOLDEN!

@LuminoZero  
Nigga please, you just activated my mousetrap card. XD

That’s SO in character for Spike. I’m in love with this writer and wish she’d write for the show, seriously.
 
Makes you wonder how much that Twilight tries to teach him just bounces off of Spike, and you can understand the kid. He gets hit with more knowledge he can handle at his age probably on a regular basis, but he finds his happy place between the impossible perfection Twi aims for herself and total slackerhood where he can enjoy himself.