randombio.com | science commentary
Friday, February 01, 2019

Why we forget words

Forgetting in the brain is not like erasing files on a computer. It's an active process.

I once spent a week trying to remember the name of the actor who played the main character in The Girl From UNCLE. I had the same issue with the actor in that famous Twilight Zone episode about a guy who survived a nuclear war because he spent his lunch hour in a bank vault reading a book. You know, what's-his-name.*

Neuroscientists have found that storing information is only half of the task of memorizing. You also have to memorize a way of retrieving it, which means (a) indexing it by its pronunciation, first letter, or some other feature, and (b) practicing. You also need (c) stress, which intensifies memories by inducing your neurons to release a molecule called cyclic AMP, which tells the neurons that the memory is really important, and not some useless drivel like where you parked your car or where that dangerous intersection is.

We are programmed to remember stressful things. We remember forever where we encounter­ed a snake unexpectedly in the wild or where we had a car accident. Knowing where there are snakes benefited the survival of our ancestors; knowing where there are car keys, not so much.

This explains why we can't remember the capital of Kyrgyzstan, but we can't forget mistakes we made twenty years ago, words we should have said, and even jokes we could have made: the unresolved or unexpressed emotion keeps the memory alive, causing the event to be rehearsed over and over. For trauma victims, this can be debilitating.

Getting stuff out of your brain is an exercise in trigonometry: the greater the distance between the two mnemonic stimuli, the more likely they are to converge on the correct neuron, assuming, of course, that the neuron still exists.

G-Shock GW-4000D-1A
Cbl is involved in the production of cytokines, which cause neuroinflammation, which causes forgetting. In these diagrams, a T-shaped arrow means inhibition, so two T-shaped arrows means the first molecule prevents the second from blocking the reaction. This pathway is very important, so it's tough to remember.

The geometric theory of memory is supported by a recent finding that the brain stores information in a geometric pattern, which scientists hope will give us a way of someday creating a thesaurus that doesn't suck.

That's why names, which are basically collections of nonsense syllables, are so hard to remember: they can only be accessed by brute force. Chemists have a much easier life. If you'd ever gotten a whiff of beta-mercapto­ethanol, which smells like pea soup that's been sitting in a septic tank, you wouldn't forget the name. Multiple sensory pathways, like scents, visual images, or even motor pathways, help the brain make locate the memory. Proper names have no such geometric cues.

I once worked in a lab where the fume hood exhaust was right next to the ventilation intake. One day someone opened a bottle of beta-mercaptoethanol in the hood. Within minutes the bureaucrats on the floor below called the fire department, thinking it was a gas leak. I don't think they liked us much after that, but they never forgot us.

Chemists remember chemical names because they have to type the names over and over in those chemical hazard forms, where they write down, for instance, that they're in possession of a beaker containing 1000 milliliters of deadly dihydrogen oxide. This information goes with the MSDS form, and it comes in really handy when the fire department comes into our blazing inferno of a lab, and they spend twenty minutes going through the four-volume binder to learn that, indeed, we have a beaker of water somewhere in the lab.

Forgetting is an active process, and specific pathways in the brain are involved in forgetting. One way this happens is through Cbl, which is a type of protein called an ubiquitin E3 ligase, which means it labels proteins that the cell no longer wants so they get chewed up and recycled. Cbl is also involved in inflammation, which is another way the brain erases things, and that means, like just about everything else in the known universe, Cbl is involved in Alzheimer's disease. In the slide above, showing the TLR4 pathway for brain inflammation, Cbl is right in the thick of it.

A friend of mine once created transgenic mice that lacked Cbl, and showed that they had memory deficits. Unfortunately, this was before the importance of inflammation in the brain was recognized, but its relevance to memory was demonstrated when some lady in the parking lot forgot which gear setting was “reverse” and drove her car through the brick wall of the animal facility where the mice were stored, killing them.

Forgetting can also be caused by AMPA receptor endocytosis and depression of synapse strength. A different type of forgetting happens in retrograde amnesia, where a person with a head injury is unable to remember the events leading up to it. This is thought to be caused by disruption of electrical signals. Substances that block protein synthesis also cause amnesia. Technically, these aren't forgetting, but failures of storage.

Words are like a rock collection: you have to take them out and clean them every once in a while. Indexing words by letter strengthens your abecedarian puissance; even more so for anyone wishing to retain fluency in a foreign language. Words that have weird sounds, like kreutzworträtsel (German for ‘crossword puzzle’) are easier to remember.

That's not always true. Try remembering Aldiborontiphoscophornia, which is the name of a character in a weird play by Henry Carey called Chrononhotonthologos; or acanthopterygian, which means a type of teleost fish belonging to the superorder Acanthopterygii. Affenpinscher is a breed of dog with pointy ears. Amentiferous means bearing catkins. Edaphic factors are the properties of dirt. And when somebody uses the word Afghani instead of Afghan, or when soldiers call a weapons cache a cachet, people with OCD might want to shriek, but the stress that creates ensures that they never forget the person who uttered that abomination.

Varangian, which refers to the Scandinavians who invaded Russia and Ukraine in the 8th century, is the word I was trying to remember. Now if I could just remember what I wanted to say about it.

* Stephanie Powers and Burgess Meredith

feb 01 2019, 5:20 am. edited feb 02 2019, 7:06 am

Related Articles

How the Internet Changes Our Brain
Our attention spans have ... um, something

On the Internet, no one can tell whether you're a dolphin or a porpoise

book reviews