How memory works (the 'magic number' for remembering) cover image

How memory works (the 'magic number' for remembering)

Dorian Minors • September 18, 2015

This is an archived article from our predecessor website, The Dirt Psychology. The idea there was to take psychological scholarship and turn it into wisdom. The Armchair Collective tries to go a little further than just psychology. As such, these articles live here in archive form, until they're updated.

In 1953, surgeons removed almost half of Henry Molaison's brain. Henry (or 'H.M.' as he was, and still often is, known) suffered tonic-clonic seizures (previously known as grand mal, an 18th century term for 'big illness') as a result of his epilepsy. Henry's brain was essentially dying as a result and one of the only remaining options was to experimentally remove the areas of the brain causing the seizures. We learned a extraordinary amount thanks to Henry's sacrifice. Unfortunately, he died soon after. Just kidding; he lived until 2008 at the age of 82. This is a rare operation, but one that is so successful that it still occurs today, albeit in another form. Let's talk about memory without a brain.

If I remove half your brain, will you remember me?

Following the operation, Henry suffered significant anterograde amnesia (he couldn't form new memories). He also suffered quite severe retrograde amnesia (he couldn't remember the last 2 years or so, and had spotty memory for the last 11 years of his past). What made H.M. particularly interesting however, is that he had a fully functioning short-term memory (he could participate in tasks and activities), and in the exploration of that, scientists found that Henry could actually learn new physical skills even though he couldn't remember learning them! This was first noticed when Henry was asked to trace a design while looking in a mirror (so everything is back to front). He found this very difficult at first (as would you), but eventually got better and better over the weeks (despite having no recollection of the task - in fact it would have to be explained to him every time).

Yeah, the guy was still reading and learning at 80 with no new memory space and half a brain. What have you done lately? Yeah, the guy was still reading and learning at 80 with no new memory space and half a brain. What have you done lately?

How to make new memories when you can't make new memories

More interesting is that Henry eventually learned how to make 'new' memories, by modifying his old ones. He was able to learn new information this way and thus, by the time of his death, happily spent his time doing crosswords (among other things). Henry taught us a great deal about memory and thanks to him we were able to learn and confirm many of our ideas about how our memory works. This article goes over the basics.

How memory works

Before we begin, let me preface this by saying that this 'multistore' model is only a very general way of looking at it and the more you want to know, the more complex memory gets. That said: there are three 'clusters' of memory; the sensory store, short term memory, and long term memory. The sensory store refers to the fact that at some point, for some time, our senses hold onto the information they are receiving long enough to figure out whether or not we need that information (more on that here). Our short term memory is a fairly controversial topic because people have all sorts of ideas about how that works. But here, I simply refer to when we pay attention to stuff from the sensory store and thus 'bring it to the table' to work on. Our long term memory refers essentially to our memory storage space. It's where we put stuff when we're done playing with it. How does it all work? Well, stuff comes into our sensory store and we decide it's important. So we pay attention to it (again, read about what makes us pay attention here). Everything else eventually ‘decays’ from your sensory store, freeing it up for the new stuff that’s already coming it.

You can only pay attention to seven things at once (the memory ‘magic number’)

In the meanwhile, the stuff you paid attention to is in the short term memory. Evidence suggests that your short term memory can essentially only maintain to seven (give or take two) things at once. To take in any more, you have to ‘chunk’ items together. That’s why it’s easier to remember groups of numbers if you imagine them as ‘123’, ‘456’, ‘789’, instead of ‘1’, ‘2’, ‘3’, ‘4’, and so on. So, if you try to take too much on, the rest gets displaced and you lose it to the sands of time. It is important to remember that short term memory in this conceptualisation doesn’t really account for the stuff you learn unconsciously (learn one way we do that, here).

Your long term memory might be unlimited

If you rehearse those seven bits of information enough (and some things are easier than others), then your brain will put them on a shelf in your memory cabinet to recall later. Or, if it comes in from your unconscious, it'll get put in a box to be recalled at leisure. However, much like a garage, sometimes you forget where you put it. This explains why you can 'forget' all about your appointment on Wednesday, but as soon as someone brings it up, all of a sudden the time, date and other associated information flood back to you. You can put anything in your long term memory, you just have to make sure it's links to other memories are strong enough that you can get it back.

It's like losing a file on your computer. Unfortunately, your brain doesn't have a 'search' function. It's like losing a file on your computer. Unfortunately, your brain doesn't have a 'search' function.
No memory is ever alone; it's at the end of a trail of memories, a dozen trails that each have their own associations" - Louis Dearborn L'Amour

You know, a lack of memory is one of the reasons incompetent people don't know how incompetent they are. And if you lose memories, you might think about trying to get them back through hypnosis, but you probably won't be able to because hypnosis isn't what you'd expect (and it's more effective than you know). Giving you the dirt on your search for understanding, psychological freedom and 'the good life' at The Dirt Psychology.

Turning scholarship into wisdom we can use at The Armchair Collective.

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Dorian Minors

I mostly do brain science. Sometimes I train honeybees. I promise they're related. I made this site because there's no reason why scholars should be the only ones to own knowledge. My special interests are interpersonal relationships, the science of community, spirituality and the brain, and the neural basis of complex behaviour. I hope this stuff is as interesting to you as it is to me. You can find out more about me here.