Ok, just my spin on that. Upper part is background stuff, lower part is solutions.
Brain? Memory? What's that?
First lets look at the brain: Your brain is a giant association machine. To work properly there are multiple sections keeping different parts of memory in different places and ways:
First, there is the immediate memory: This keeps your immediate thoughts and impressions for split seconds or seconds only and is not too large. It could be compared to the on-board-cache of the CPU in a computer. Its first part, the sensory register keeps stuff together for milliseconds, to e.g. allow you to "see" a person, rather than a varying set of blotches of color. Since the immediate memory is kind-of interlinked and shares "hardware" with the next one, people often skip talking about it and start straight with:
The short-term memory: Here memories are kept for 20-45 seconds. They are partially filtered and are on "speed dial", so to say. Often the intermediate memory is also counted into short-term, raising the mark to roughly two minutes and largely filtered. Since this is also where consolidation takes place, parts of this memory are refreshed and refreshed again, while filtering out unnecessary stuff. (These re-runs are why people talk about the "quarter-hour" of short-term memory). This is comparable to the RAM-bars in your PC.
Then there is the the long term memory: This is the big hitter. Everything and anything remembered, that is older than a quarter-hour is either stored directly, or reconstructed "pseudo-memory", coming from here. This is your hard-drive, SSD, tape or whatever.
So: Memory problems?
Let's look into the types of memory loss possible:
- Immediate memory loss:
Yeah, not even really on the list. If your sensory register doesn't run, sounds
or images can't be processed. Not talking about illusions (that happens far later)
but the basics: "ooh, a red triangle, a blue circle". That stuff ... still is
higher up the chain, but it illustrates the point. If the rest of your immediate
memory doesn't work, you're effectively dysfunctional. Possible, but not for your story.
- Anterograde amnesia:
If your short term memory is not stored properly, you still can work or experience most simple stuff.
This can make you appear normal, but you loose what is older than a few minutes.
As your memories never really are built, A) recovering them later is impossible
and B) Instead of getting lost later they will be lost from the start of an episode.
Many Benzodiazepines can cause it, as can most hypnotics (sleeping pills),
some infections (like Typhus) and organic bromides.
Thiamine deficiency is a good canidate as well, as it can trigger Korsakows syndrome.
- Retrograde amnesia:
This would remove past memories, rather than preventing new ones.
REASONS usually include physical or emotional trauma, as well as epileptic episodes.
Physical traumata would usually severe the memory permanently. While you could,
in theory, recover if not the memories them self are destroyed but just the
associations leading to them, that is so unlikely it's basically handwavium.
- Dissociative amnesia:
This is not actual memory loss, but your brain trying to keep you save.
REASONS: Usually caused by emotional trauma or prolonged high-stress situations.
This type of memory loss can be reversible.
- recalling is blocked:
There are three ways of loosing memory:
A) you didn't write it,
B) you lost/overwrote/destroyed it, and
C) you cannot retrieve it.
This is mostly called in by the other points, but in theory a chemical could just
prevent accessing memories. However this would affect pretty much all memories
equally, so not for your story either.
You could have blockages as well, but they would either be gone fast,
or permanently damage your brain. Also they're hardly specific to certain memories.
Therefore you should go with either anterograde or dissociative amnesia.
The ditch-finders guide presents: Why not to live on Dementia-4!
1. Infections: Oh no! You got MEMOs!
The "Memory eating micro organisms" are really nasty f's! These microbes consume
Thiamine while keeping the glucose level high. As they sync reproduction (like Malaria),
and they burst while reproducing, every month or so you get some days where you
can build new memories, before the drop in Thiamine triggers Korsakows syndrome
and prevents new memories from being formed. Also, as Thiamine (or vitamin B1)
is a necessary co-enzyme for glucose metabolism, you get a monthly diabetes.
Deadly if untreated for too long, since it breaks your glucose metabolism.
While not deadly like MEMO, the MEMO-2 virus produces Diazepam (Valium).
This too prevents building new memories (aka: anterograde amnesia). Also it may
invoke addiction if untreated. Keeping a few vials of Flumazenil (as antidote)
2. Plants: Dont go near the scarecuddle tree!
The scarecuddle is an extra-ordinary piece of an erect middle finger by nature.
The female tree looks like an overgrown appleberry tree, even mimiking the fruits.
These taste slightly of almond and have a orange tinted core with one stone,
not many green tinted apple cores. If you plucked one: drop it and run as fast
as you can.
The scarecuddle will release strong pheromones from the outermost brances to
scare you away. The core however will release Midazolam. This is a muscle relaxant
and anti-panic agent. If you dont run fast, you will fall asleep, pass away and
become nutiens for the tree.
You should constantly call out "scarecuddle" while running, as the Midazolam
prevents your long-term memory from forming and you need to keep the reason
you're running in short term memory.
Male scarecuddle is harder to detect, as it looks quite different. It grows in
large, connected woods, all sprouting from each other like bamboo. About once a
month the unassuming looking bushes produce red-to-black pseudo-berries,
while there is a slow buildup of Midazolam and an alluring scent.
Touched when ripe, the pseudo-berries pop with a loud bang and send barbed anthers (pollen-bags) flying.
The noise, the pain of the parbed anthers and the yperite (mustard gas)-like gas
inside sends animals running for the next clearing ... which usually contains a
2.b Psychodelic fungi:
Enough said. No, of course you do NOT eat shrooms. However, when the Fairy-Dust mushroom pops, it showers you in its spores. You're tripping for a month straight.
3. Animals: The cute looking "Fluffed scavenger"
The "Fluffed Scavenger", also known as "Carrion Bunny", is an unassuming looking
animal looks a bit like a fluffed up version of a rabbit, hence the name.
Individual animals are highly prized as stress relievers as their musk contains
anti-depressants and calming agents.
Its pack, also known as fluffle, can contain between 8 and 60 members. The term
herd would be misleading as it is purely carnivore. However Instead of hunting,
this the only known pack scavenger: When a predator has killed, a fluffle
may spray their musk and sedate the predator to steal their kill.
Blood-Monkeys are immune to this. Instead they seem to work together, with the
Carrion-Bunny distracting and partially sedating the prey. The Blood-Monkey,
having an easier time hunting, will break open the prey and its bones, leaving
the brain, bone marrow and some of the meat as "payment".
Keep in mind that in its bi-monthly mating cycle the musk levels rise and that
if you own more than one, the passive musk may start inducing forgetfullnes.
There's a reason why fluffle-catchers wear gas masks! An entire fluffle may well
produce enough musk to cause anterograde amnesia!
Mem-Writer needs update!
If you use a Mem-Writer older than model 4, the diogenes see is off-limits for you!
The gysir system produces a very weird magnetic fluctuation pattern which old
models can pic up as modified stack-reset signal. As stack-reset signals are now
obsolete you shouldn't run into trouble, but be carefull anyway.
A stack-reset signal will start a timeframe on the keep-stack command. Once the
reset-signal arrives, all memories in the timeframe, that were not previously
backed up, are overwritten or deleted.
(This is utilized in court-rooms and some NDAs. As well as by the mafia of course.)
Mem-Writer crashed: resuming stable task
Once you go down to the details, a Mem-Writer is mainly some software. Due to
the extra-ordinary magnetic fields, your Mem-Writer cannot write a proper
back-up log. As it overflows, it crashes and tries restoring from the last valid
state. Once satisfied your Mem-Writer may try creating a new safe state.
Two options from here:
- The Mem-Writer is a transparent overlay over your memory. Since it cannot
set the date correctly however, the memories are (temporarily) hidden. Turning
it off will restore your access to it, but once turned on again its hidden again.
- Steve from IT was very overworked. With 3h sleep in the entire week he
accidentally swapped source and target on consistency-restore-events. This means
that once a restoring of consistency is requested, the Mem-Writer overwrites the
brain. This bug is hard to track as nearly no-one uses consistency requests.
However the research team didn't use "create backup" but "restore consistency"
as backup function. Why? No one knows. Probably a mistake, as it will them their
memory of these days permanently!
You're the backup
No-one knows what's inside the singing caves. No one ever returned from them.
Since we never knew why, we sent a backup. Call it clone, call it backup, just
You're a Trekky accident
The teleporter broke down while you where on the way.
They immediately try to fix it, while you look around.
A month later they manage to beam you up, however the returned version is the
emergency backup of the teleport. The real you, with the experience and stuff?
Well sh*t you've just dissolved it. Stuff happens mate, just be glad you only
lost a month.
You're a Trekky hack-sident
Some MF is hacking into the transporter matrix!
Sex-Drugs-Rock'n'roll? Or rather "Be-My-B*tch!" ? Doesn't matter.
They got you drugged with something that makes you "day sleep-walk". You don't,
or hardly remember anything.
6. Primal Fear/Regret
Something or someone is really disturbing. What ever it was, it triggered not
only your own dissociative amnesia, but did so with your entire team. For this
to happen over a certain period of time it had to be really bone shaking!
I'm sure there's more, but that's my two pence.