Tag: long-term memory

Earlier this month, I linked to a study showing that declarative and procedural memories correspond with different brain-wave frequencies.

This week: another study making a similar point. Researchers have found that frontal, temporal, and medial temporal lobes align neural activity at lower frequencies as new memories are formed. (At higher frequencies, neural alignment is weaker.)

Networks and Brain Waves

As lead author Ethan Solomon says,

This suggests that, for someone to form new memories, two functions must happen simultaneously: brain regions must individually process a stimulus, and then those regions must communicate with each other at low frequencies.

I suspect that over the next few years, our understanding of long-term memory formation will move in this direction. That is, we will increasingly combine the study of synapse formation between neurons with the study of frequency alignment among brain regions.

That account will doubtless be more complex. But: if it’s more accurate, that complexity will ultimately be more helpful to us all.

Looking Forward to 2nd Grade

When I was in grad school, Kurt Fischer often said “when it comes to understanding brains, we’re still in first grade.”

He meant that the brain is just so complicated, we have only just begun to understand it.

For teachers interested in neuroscience, this truth has a powerful consequence. Much of what we learn about the brain today will be understood differently next year. It might be quaint in ten years.

 

Newcomers to the field of psychology and neuroscience often want to learn as much as they can about a student’s memory system.

After all: when students learn something new, that means their memory has changed. So, if we know how memory works, then we’ll know how learning happens.

Alas, it’s not that simple.

It turns out that we have many different memory systems. We can’t simply learn how one of them works; we have to understand them all.

Key Distinctions

In the first place, we need to distinguish between long-term memory, and other short-term memory systems.

For example: if I ask you for your business phone number, you pull that number out of your long-term memory. After all, you know it quite well.

As I then walk across the room to write that number down, I hold that number in my short-term memory. (Probably I’m rehearsing it in my head, or even saying the numbers quietly.)

If, however, I decide to engage in some quick mental exercise, I might try to add together all the digits in your phone number. In that case, I’m not only holding those numbers in short-term memory, I’m also combining them in working memory.

I haven’t even written your number down yet, and already we’ve got three at least different memory systems at play.

Subtler Still

Of course, we can subdivide each of these categories in many different ways.

Long-term memory, for instance, includes at least two sub-categories.

Explicit memory records facts and events. I know that the Ideal Gas Law states that PV=nRT (fact). I know that yesterday was my mother’s wedding anniversary (event).

Implicit memory, by contrast, records processes: how to do things. Muscle memory is implicit. So is your knowledge of your native language’s grammar. You know how to juggle, and how to conjugate the auxillary verb “should”–even though you probably can’t say exactly how you’re doing those things.

In schools, we seem to focus a great deal on explicit memory: we want our students to know all sorts of facts.

However, we also want them to learn procedures: how to integrate a quotation into a subordinate clause, or how to solve for three variables with three equations.

Initially, our students learn these skills explicitly, but with enough practice they can do them without having to think about it. At that magic moment, their explicit memory has become implicit.

Brain Structures and Memory

We’ve known for a long time that explicit and implicit memory formation takes place in different parts of the brain.

Those of you who know the story of Henry Molaisson know that surgeons removed his hippocampi to relieve his debilitating epilepsy. The operation (mostly) cured this medical problem, but created a profound cognitive problem: he could no longer form new explicit memories.

That is: if he practiced drawing a complex figure every day, he didn’t remember from one day to the next that he had practiced doing so the day before; he couldn’t remember the event.

However–and here’s the key point–HE GOT BETTER AT DRAWING THE FIGURE. That is, he didn’t form explicit memories of practicing, but he did form implicit memories of the new skill. He knew how to do it.

Clearly, the hippocampi are essential for explicit memory formation, but not for implicit memory formation.

Larry Squire’s article Memory systems of the brain: A brief history and current perspective provides a helpful overview of different memory systems, and the places in the brain that house them.

(The Henry Molaisson story is often told. Although controversial, Suzanne Corkin’s book Permanent Present Tense is probably the best place for an extended exploration of HM’s life, and the scientific information learned from it.)

Today’s News

A recent article in the journal Neuron argues that explicit and implicit memory differ not only in their location in the brain, but also in the frequency of their neural signatures.

As you can see in the diagram above, gamma waves oscillate quite rapidly–up to 100 times per second–whereas delta waves oscillate slowly–fewer than 3 times per second.

(Wikicommons has a helpful visualization of different oscillation rates here.)

This article suggests that explicit memories show an increase in the alpha/beta range (10-30 Hz), whereas implicit memories produce an increase in theta waves (3-7 Hz).

In other words: explicit and implicit memories record different kinds of information, operate in different parts of the brain, and produce increases in different kinds of brain waves.

As of yet, there are no specific teaching implications to these research findings. However, they underline the point where this argument started: we can’t simply study a student’s memory system, because each student has so many (and so complex) memory systemS.

Little wonder, then, that teaching and learning can be so challenging. And, of course, so much fun.

Imagine yourself following a route that you know quite well: perhaps your morning commute. You take your car out of your garage; drive past the Dunkin’ Donuts, past the old movie theater, past the grocery store; you park in your favorite spot, walk through the lobby, down the library corridor…

You can easily think of these places in order because you’ve followed this same path hundreds of times. Well, an ancient memory trick takes advantage of your well-rehearsed visual memory.

If you have–say–a list of words to memorize, you can take some time to associate each word with those places. For example, if you have to memorize the words “tomato, airplane, tuba,” you can create a vivid picture of a tomato splatted on your garage door, an airplane flying over the Dunkin’ Donuts, and a tuba band marching in front of the movie theater.

You can then recall those words simply by mentally following your morning commute to work.

Even if you have a very long list of words, this method still works; you can, after all, visualize many, many places along this familiar route.

The Research Questions:

This memory trick–called “the method of loci”–has been around for centuries. Memory champions typically win memory contests by using it. But, can just anyone do it? Do you need to be born with a special memory talent?

Martin Dresler’s research team answers some of these questions. He started by scanning the brains of memory champions while they did some memory feats, hoping to discern neural patterns associated with excellent memory.

He also scanned some non-memory experts as a baseline for comparison.

Sure enough, he found connectivity patterns that helped distinguish between these two groups.

Next, he trained those non-memory experts in two memory techniques. One group practiced the method-of-loci approach for 40 days, 30 minutes each day.

The other group used a well-established short-term memory exercise. (Perhaps you’ve heard of the n-back test.)

What did the researchers find?

The Research Answers:

First, the method of loci really helped. Those trained in this method more than doubled their ability to remember words on a list. (Those who did short-term memory training saw little more improvement than control subjects.)

Equally interesting: the method of loci training created the neural patterns that Dresler had found in the memory experts.

That is: this training paradigm BOTH helped participants remember more words AND changed their brain connectivity patterns.*

In other words: we have two really good reasons to believe that method of loci training helps people remember word lists.

The Inevitable Caveat

If you’ve read this blog for a while, you know I’m going to point out a downside sooner or later. That moment has arrived.

First, the method of loci helps students do something we don’t often ask them to do: remember lists of unrelated words. It’s a cool party trick, sure. But, at what point do we care if our students can do such things?

For example: I suspect the method of loci could be used to help students learn all the elements in the periodic table in order. But–why would we want them to do that? Would such knowledge meaningfully improve their understanding of chemistry?

Second, notice the extraordinary about of time the training took: 30 minutes a day for 40 days! Imagine what else you could do with those twenty hours.

So, I’m not exactly opposed to teaching the method of loci; I’m just unimpressed by it. The method requires lots of training time, and creates a benefit that doesn’t help very much.

If, by the way, you have a good use for this method, please let me know. I’d love to hear about its practical classroom uses.

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• Although it’s true that this training changed the brains of those who participated in it, it’s also true–as I’ve written before–that any activity repeated at length changes your brain. This finding is interesting, but not exactly surprising.