A cartoon of a man is shown opening a door.


Even walking through a door will make you forget—unless the door opens onto a toilet, I suppose, though approaching a toilet in outer space will still require you to keep your wits about you.

Unless you completed your psychology courses recently, the essential facts of forgetting were probably neglected. The main point about forgetting is that it’s a helpful feature of learning, not a bug. It’s worth noting that it’s not passive decay, for the most part, but active information processing. It’s not the reverse of learning. It offers a fascinating glimpse into the relation between the brain and psychological experience.

Since we all forget events, words, and movements, we might suspect that forgetting has its uses.  It’s sometimes frustrating (just one effect of distraction), controversial, and often unconscious.  But for better study skills, managing forgetting is as important as managing learning!

These aspects of forgetting barely begin to cover the territory. Interesting stuff about the difference between normal forgetting and abnormal amnesia, the problems of remembering too much, and drug effects would fill a book as well.

A checklist with all the boxes checked.

BIO: Before we look for causes of forgetting, it might be worth taking a brief look at how memories are formed. Long-term potentiation (LTP) pinpoints memory formation to individual synapses in the hippocampus, and that is explained at length there. This interesting article explains how the cerebral cortex performs a complementary role.

We might also include the basal ganglia, which usually are tagged with the control of stereotypical or overlearned action patterns but also retains them (along with the cerebellum) and supports implicit memory.

We could go on. How does such a brief event as LTP store experiences that go on for seconds or minutes? Since we can’t store every experience, how do we keep storage manageable? And–to return to your own point–how are memories handed off to other structures?

But enough about memory formation. At a microscopic level, it’s clear that synapses form in the brain and are altered by experience. As a result of disease or disuse, a kind of glia called microglia nibble at some synapses, performing a kind of synaptic pruning that makes weak synapses harder to retrieve.

Enough about the brain, which is but a tiny part of our biological makeup! Do we forget in other parts of the nervous system—the spinal cord, the enteric nervous system? Can we forget unconscious memories?

PSYCHO: Two salient features of forgetting are that it is active and adaptive.

Incidentally, the article from Knowable magazine mentioned the famous forgetting curve of Hermann Ebbinghaus. The forgetting curve is a great way remind ourselves of valuable old ideas. It was even replicated fairly recently!

It’s worth remembering that the forgetting curve of Ebbinghaus was obtained using nonsense syllables (DAF, WUG, etc.) as learning items. We don’t forget an ice cream flavor we like as fast as nonsense syllables, much less the training* that companies pay for (unless they consist of nonsense syllables). But it’s important to realize that grouped nonsense syllables are forgotten exponentially and quickly. The testing is boring for participants, but the details do matter.

We forget for a number of reasons. It can be hard to remember things under stress, not because of the forgetting curve but the cortisol, so paramedics, firefighters, musicians and special operations forces** resort to techniques like overlearning and stress inoculation. (Stress changes gene expression in the brain on a minute-by-minute basis. A little stress helps mental performance, but too much hinders it. Stress is good for us until it isn’t. Researchers are still trying to come up with an explanation at a neural level.)

Memories can be obliterated when the synapses that associate them with other neurons in a long-term memory network are disconnected by microglia. Then they are truly gone. While this could happen as unused synapses are expunged during sleep, it’s pretty drastic, often associated with pathology.

Both normally and pathologically, the usual cause of forgetting is trouble with retrieval. Instead of destroying memories, forgetting makes them harder to bring back to mind.

Retrieval failure is an inability to find a memory that is stored but inaccessible. Disuse makes memories hard to recall. Have you experienced the tip-of-the-tongue (TOT) phenomenon recently? That’s a retrieval failure. With the TOT or any other information you want to remember, practice retrieving it. It will help whether you are successful or not!

Another kind of forgetting we can blame on retrieval failure is interference. Proactive and retroactive interference impair both working memory and long-term memory.

Retrieval from working memory is instantaneous, while retrieval from long-term memory can be laborious. (What was the name of your third-grade teacher?) We rarely lose stored memories, but they can become very hard to recall.

Retrieval is not an obvious process sometimes. An alternative explanation of the TOT is retrieval-induced forgetting. When we retrieve one memory, we inhibit the retrieval of similar, competing memories. While this minimizes interference, it causes a completely unconscious type of forgetting.

We may also fail at retrieving because of negative priming. Priming, negative or positive, is an important memory process that illustrates the associative character of long-term memory, but I’m going to halt the dive into ever-more-obscure retrieval failures at this point or we’ll end up discussing brain fog, which is just pop psychology (doesn’t mean it isn’t real, just not a valid diagnosis).

*The corporate world is sometimes convinced that training is forgotten just like nonsense syllables, so don’t train on Friday! Workers will supposedly forget 90 percent of their training in a month, yet they retain 20 percent after 30 days! And after two days they’ll retain a quarter of what they learned, although their graph seems to say it’s less. The best teachers must be in CPR classes, because their training lasts 3 months. Even longer for defibrillator training! Maybe those classes aren’t all nonsense syllables? And then there is the steep learning curve

**Even us? Say it isn’t so, Kendra Pierre-Louis!

SOCIAL: We remember what makes sense to us, and what makes sense often depends on what our friends say. This influence can bias retrieval and even cause forgetting.

Nowadays, what makes sense is often remembering where a memory can be found instead of what its content may be. This is transactive memory. In the days when external information was mostly confined to long words in the dictionary and short notes like shopping lists, external devices were helpful. That may be changing.

Just as seriously are our mental blanks when we meet an acquaintance after an absence or in new surroundings, especially if our shared memories now diverge.

Is there a truly social memory, a collective memory shared within a group? Certainly there are similarities among the individual memories of people who have shared experiences. It’s possible as well to find collective memory that supersedes any individual memory, as in an ant colony. The process of collective forgetting has not gotten much attention in research.

However, the notion of a “collective unconscious” proposed by Jung is an imprecise metaphor for a cognitive ancestry that some have labeled a myth.

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