My story requires a team of human explorers on a far-away planet to repeatedly lose their latest few months worth of memories through some natural phenomenon (or perhaps equipment malfunction) while being otherwise unimpaired.

I am assuming a high-tech sci-fi environment where interplanetary travel and things like cryo-sleep are common.

I have been thinking along the lines of some strong magnetic field due to a sun storm, or similar events. The humans would have to go into sleep/hiding for the period, and their latest memories would be erased.

The problem is to make it biologically somewhat plausible. If they were robots with a completely sequential memory, I could assume that (part of) their in-built memory store gets wiped and they get a stored factory reset or something. But with human memories, I am unsure how one could "set them back" to their state from a few months ago, given that memories are so subtly intertwined with learning and cognitive functions.

How could humans repeatedly lose their latest memories in a biologically somewhat plausible way in such a setting?

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    $\begingroup$ To loose means to let free from restraints, e.g., loose an arrow. To lose means to make something cease to be in one's possession, e.g. to lose money. Corrected. $\endgroup$
    – AlexP
    Commented Jun 29, 2022 at 14:12
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    $\begingroup$ Does everyone lose the same memories? Or is it patchy? For example you forget the party we were at and it turns out no-one remembers? Or you forget that party and I remember? $\endgroup$
    – Willk
    Commented Jun 29, 2022 at 15:57
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    $\begingroup$ I don't think "hard science" tag is what's intended here. This question isn't answerable in line with that tag (equations and citations). Science-based would be a better fit. $\endgroup$
    – Zeiss Ikon
    Commented Jun 29, 2022 at 16:10
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    $\begingroup$ You don't lose them, you lose the ability for short term memory to become long term memory. "Memory impairment from marijuana use occurs because THC alters how the hippocampus, a brain area responsible for memory formation, processes information." nida.nih.gov/publications/research-reports/marijuana/… $\endgroup$
    – Mazura
    Commented Jun 30, 2022 at 5:29
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    $\begingroup$ @Willk everyone loses the same memories, i.e. they are effectively re-set to their mental state of some weeks/months prior to the memory-loss event. So the cause would have to be something that is likely to affect all of them pretty equally. $\endgroup$
    – Scriddie
    Commented Jun 30, 2022 at 9:17

8 Answers 8


Backup Restoration

In a far future world, people make backups (periodically, perhaps daily in a hazardous environment) to protect their memories and identity in the case of their body being killed (see Altered Carbon series or books, Quantum Vibe web comic, the Hotline series of novels and stories by John Varley, among others).

Anything that requires restoration from backup will lose all memories newer than the last backup -- if you're backing up once a week, you could lose anything from a few hours, to several days, for instance. This has other implications -- many folk used to this life pattern will have a strong desire to find out how they "died" if they wake up in a reconstitution chamber and the clock display shows they've lost time -- especially so if the loss is longer than their usual backup interval. In some cases, this might become an obsession!

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    $\begingroup$ Humans land on planet. Base camp has regenerator. Keep sending expeditions, expeditions keep dying. Can't figure out why because the memories never return. Could make for a very neat story. $\endgroup$ Commented Jun 29, 2022 at 22:56
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    $\begingroup$ @Scriddie backup restoration pod $\endgroup$ Commented Jun 30, 2022 at 10:19
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    $\begingroup$ @Scriddie which implies either backup bodies as well, or rapid cloning, or they're all androids to begin with... $\endgroup$
    – Zeiss Ikon
    Commented Jun 30, 2022 at 10:59
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    $\begingroup$ @MadPhysicist Actually, the "keep dying, can't figure out why because the memories are lost" was covered by Cory L. Doctorow -- Down and Out in the Magic Kingdom. $\endgroup$
    – Zeiss Ikon
    Commented Jun 30, 2022 at 11:03
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    $\begingroup$ In fact, something similar (with complete copies of body and mind) was covered in Fred Pohl's Cuckoo novels, The Farthest Star and Wall Around a Star. The things you'll do to pay the rent... $\endgroup$
    – Zeiss Ikon
    Commented Jul 1, 2022 at 14:23

This effect is a common one for people who have had clinically safe doses of opioid drugs like oxytocin and fentanyl.

It is really quite remarkable to see it play out in real life with people who have received it at levels sufficient to alleviate pain while not producing unconsciousness seemingly interacting fairly normally and recorded on video doing so, then an hour or so later having no recollection of having done so.

Also, the memory impairment effect continues to operate for up to a few hours after the dose has been metabolized to the point that it no longer produces a pain killing effect and no longer notably impairs physical functioning.

The chemical could be present in the necessary low doses from all manner of local exo-botany: pollens, aerosols near water falls or turbulent rivers from water plants, ubiquitous bacteria, protozoans, tiny mostly harmless mites, etc.

The poppy field scene in "The Wizard of Oz" comes to mind as a fictional analog of this kind of thing.

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    $\begingroup$ I was going to say weed; you went straight for the Fukitol, +1 $\endgroup$
    – Mazura
    Commented Jun 30, 2022 at 5:24
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    $\begingroup$ You went for the comparatively innocent Wiz of Oz, my mind went to Darkover Landfall. The summary there doesn't capture the many mysterious pregnancies that it produced. $\endgroup$ Commented Jun 30, 2022 at 11:19
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    $\begingroup$ Alcohol in sufficient quantities can produce such blackouts. I've heard someone describe "coming to" in the midst of sex with someone else. They were actively involved but had no memory of anything prior to arriving at the party earlier that evening. The other person had no idea and instantly stopped when it became clear what had happened. $\endgroup$ Commented Jun 30, 2022 at 17:47
  • $\begingroup$ @NotEntirelySerious I don't disagree but have a harder time coming up with a plausible mode of transmission that wouldn't quickly be circumvented. Still it is proof of the principle that a multiple biochemicals can have this effect. $\endgroup$
    – ohwilleke
    Commented Jun 30, 2022 at 20:42

You can use the following facts from neuroscience:

  1. Perhaps the most famous patient in neuroscience is Henry Molaison (patient HM) who had his hippocampi and surrounding regions surgically removed in the 1950s to cure his epilepsy. His epilepsy was cured but he could no longer make new memories.
  2. The current standard model of memory consolidation sees memories initially stored in the hippocampi and then gradually transferred to the cortex.
  3. Transcranial magnetic stimulation (TMS) is a modern non-invasive brain stimulation technique in which neurons are stimulated by the electric currents generated by an external magnetic field.

You can combine these so that e.g. the strong magnetic fields caused by solar storms that you suggest excite the neurons in the hippocampus as in TMS, scrambling the recent memories stored in there and interrupting the consolidation process, reverting your characters' memories to whatever they had a week or two ago.

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    $\begingroup$ interrupting the process of memory consolidation sounds nice! That would allow for the people to appear to have functional memory for a while and still lose them eventually. Thanks for the links! $\endgroup$
    – Scriddie
    Commented Jun 30, 2022 at 9:23
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    $\begingroup$ hippocampus +1. TMS +3000. "The greatest immediate risk from TMS is fainting, though this is uncommon. Seizures have been reported, but are rare.[11][19][20] Other adverse effects include short term discomfort, pain, brief episodes of hypomania, cognitive change, hearing loss, impaired working memory, and the induction of electrical currents in implanted devices such as cardiac pacemakers." $\endgroup$
    – Mazura
    Commented Jun 30, 2022 at 9:25
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    $\begingroup$ Phineas Gage is a strong contender for "most famous patient in neuroscience", he survived getting an thick iron rod driven through his brain and recovered to the point of talking and walking again ! $\endgroup$ Commented Jun 30, 2022 at 15:03
  • $\begingroup$ +1 Came here for HM. You want hard-science-fiction about forgetting recent memories? Here's not only a real life individual with this property, but a real life individual who was subject to so many well documented experiments exploring the phenomena that he is known by his initials in the greater neurological community! $\endgroup$
    – Cort Ammon
    Commented Jul 1, 2022 at 15:53

Anterograde amnesia

This is a form of memory loss that prevents an individual from forming new memories of things that occur after the specific event that caused the amnesia. Importantly, memories from before the traumatic event still remain, so your explorers will still remember who they are, why they're on the alien planet, etc.

This ailment can be caused by certain kinds of drugs. Perhaps one of these drugs has been placed in their food supplies by unscrupulous people before the explorers left civilization (a la Alien trilogy). Or perhaps a sister compound exists in the local environment, which the explorers have become exposed to, whether deliberately or not. Or, stretching the bounds of plausibility, perhaps some kind of human interaction between the explorers -- possibly in response to some external stimulus -- has caused it through a psychological mechanism. (What makes that implausible is that all of the explorers would suffer the same very rare symptom.)

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    $\begingroup$ Note that this is the condition which the protagonist in Memento has, so it's likely to be recognised and understood by readers. $\endgroup$
    – Dan W
    Commented Jun 30, 2022 at 12:49
  • $\begingroup$ Note also that having to work with Christian Bale is the kind of traumatic experience that might legitimately cause multiple people to all suffer from anterograde amnesia. $\endgroup$
    – Tom
    Commented Feb 5, 2023 at 0:30

Dinoflagellate toxin.

Dinoflagellates are protozoans and some make toxins. "Red tide" is the best known manifestation of this - a bloom of dinoflagellates and consequent mass death among fish. I have never seen anything to state that the fish kill is somehow helpful to the dinoflagellates; I think the toxin is a normal defense they have and when they bloom there is a lot of toxin. Red tide toxin can get airborne and affect people on land too. I visited a beach where there was red tide to see the fish kill and had to leave because my eyes hurt.

Pfeisteria though is supposed to use its toxin to parasitize fish - the neurotoxins stun the fish and then the pfeisteria can make sores and eat. These toxins very much affected people on the land with poisoning type symptoms. Weirdest of the symptoms were learning and memory difficulties.

Learning and memory difficulties after environmental exposure to waterways containing toxin-producing Pfiesteria or Pfiesteria-like dinoflagellates

Background: At the beginning of autumn, 1996, fish with "punched-out" skin lesions and erratic behaviour associated with exposure to toxins produced by Pfiesteria piscicida or Pfiesteria-like dinoflagellate species were seen in the Pocomoke River and adjacent waterways on the eastern shore of the Chesapeake Bay in Maryland, USA. In August, 1997, fish kills associated with Pfiesteria occurred in these same areas. People who had had contact with affected waterways reported symptoms, including memory difficulties, which raises questions about the human-health impact of environmental exposure to Pfiesteria toxins...

Results: People with high exposure were significantly more likely than occupationally matched controls to complain of neuropsychological symptoms (including new or increased forgetfulness); headache; and skin lesions or a burning sensation of skin on contact with water. No consistent physical or laboratory abnormalities were found. However, exposed people had significantly reduced scores on the Rey Auditory Verbal Learning and Stroop Color-Word tests (indicative of difficulties with learning and higher cognitive function), and the Grooved Pegboard task. There was a dose-response effect with the lowest scores among people with the highest exposure. By 3-6 months after cessation of exposure, all those assessed had test scores that had returned to within normal ranges.

It is not a stretch to think that drugs or molecules affect learning and memory does. Oxytocin is made by our bodies and can memory creation. Benzodiazepines are used to suppress the creation of memories of unpleasant experiences.

In your world there is something in the air. I could imagine a plant analog might produce a neurotoxin to discourage herbivores (which is probably what the dinoflagellates are doing too). You could pattern it along the lines of Pfeisteria. Or maybe your explorers are not laying down memories, or when they get exposed recent memories fade.

An interesting fiction could have the neurotoxin act like oxytocin. Oxytocin is a complicated molecule and in addition to memory affects higher level social behaviors as well as some purely physiologic behaviors.


Some form of psychogenic amnesia (repressed memories for a period lasting anywhere from hours to decades) seems to fit the time frames you are envisioning. Nicely, it is defined by no structural brain damage but instead by some form of psychological stress (or else hypnotic suggestion). Importantly, the ability to create new, long-term memories is not impaired, so your characters could seem to be functioning normally even though memory gaps existed. For a cause, you could imagine various scenarios:

  • A chemical or biological agent builds up in the brain, causing a physiological stress response and producing a background level of paranoia, at some point having a sudden upsurge that creates a nightmare-like response. In other words, even though there is no real traumatic event (or at least not something normally considered THAT traumatic), the characters would slowly begin to have an undefined, repressed, but physiologically-traumatic dread, and when the compound dramatically peaks it would repaint the past few months as unendurably terrifying (and therefore become repressed and unable to be recalled). Whatever agent induces this could be tied to your solar-storm cycles or other events based on chemical reactions or biological life cycles. There could be other bio/chem compounds making the characters' ability to cope with psychological trauma much weaker, explaining why the entire team responds with repressed memories rather than just some of them.
  • Some normal, everyday activity the characters have been engaging in suddenly become nightmarish, e.g. they realize the plant fibers they've been using for clothing and bedding are actually living parasites that have been invading their bodies or some other, similarly horrific discovery, making the entire experience since they began a nightmare trauma and thus repressed. I mean, now that they know what those weird, warm and ticklish sensations they had been vaguely noticing all along really were about...
  • Some kind of drug-enhanced hypnotic suggestion was implanted on the team members in advance, such that if anything happened that would jeopardize the mission, they could forget and start over. Perhaps some sort of safety mechanism, in case of PTSD making team members unable to function in their vital roles. The periodic onsets could be tied to malfunctioning equipment (e.g. an AI that is triggering the hypnotic reset on everyone based on faulty reasoning about unanticipated, periodic events). Kind of a kinder, gentler, HAL response?

Ok, just my spin on that. Upper part is background stuff, lower part is solutions.

Background stuff

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:

  1. 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.
  2. 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. REASONS: 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.
  3. 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.
  4. 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.
  5. 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.

Sci-Fi reason?

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) is advised.

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 female scarecuddle.

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!

4. Tech:

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:

  1. 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.
  2. 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 call it.

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!

5. (Fr)Enemies

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.


Korsakoff's Syndrome

Per John's Hopkins Medicine, "Korsakoff's syndrome is a disorder that primarily affects the memory system in the brain. It usually results from a deficiency of thiamine [...] Patients have great difficulty learning and retaining new information as well as problems recalling memories from the recent past."

Korsakoff's is described well in Oliver Sacks' book The Man Who Mistook His Wife for a Hat in the chapter "The Lost Mariner", in which Sacks covers a patient known as Jimmie G., who lost the ability to form new memories.

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    $\begingroup$ Welcome David. Perhaps you could clarify how this could occur "repeatedly" and act to obliterate months worth of memories. $\endgroup$ Commented Jul 1, 2022 at 4:19

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