Thinking about happy memories might make you feel happy.
But not all memories are pleasant.
Some things are just embarrassing, like that time I peed myself in third grade.
And some unpleasant memories can be a lot more serious and traumatic.
You might even wish you never had to remember a particular experience ever again.
That’s the idea of the eternal sunshine of a spotless mind, which is based on a line
from 18th-century poet Alexander pope: erasing certain memories might make you happier.
It’s more than just avoiding or suppressing a thought – you’d actually be incapable
of remembering that thing anymore.
It’s just… gone.
And even though scientists haven’t yet come up with a selective, permanent delete button
for memories, they probably could, someday.
It all has to do with how we forget things -- and the fact that we seem to be able to
do it on purpose.
It’s easy to think of forgetting as a passive process – it’s not like you tried to
forget where you put your keys yesterday.
The passive kind of forgetting might be annoying the next time you’re trying to find your
keys, but it can also be useful for your brain.
If you remembered everywhere you parked your car in the last month, for example, you might
be all confused when you were trying to figure out where you parked your car today.
Was it by the fire station? No… that was last week.
Maybe the hotel? Or was that yesterday?
You see the problem here.
This kind of passive forgetting isn’t really something you can control. But turns out that
there are active ways to forget things, too.
It’s kind of like the opposite of memorization.
So, researchers have been trying to test how that happens, because if we understand more
about how it works, we might be able to control it.
Thing is, studying humans is difficult. We’re unpredictable, so it’s hard to get the same
results every time.
Studying memory is even harder. For one thing, two people never have exactly the same
memory, even of the same event.
They’re seeing it from different perspectives, and their brains are focusing on different things.
That’s why psychologists have developed artificial memory tests to use in studies
-- they help model how our memories work, but on a simpler scale, making results easier
to replicate.
One of those tests is called the Think - No Think Paradigm, which is based on the idea
that repeatedly stopping yourself from thinking about a memory should eventually force you
to forget it.
It’s kind of counterintuitive -- like, I could tell you to try really hard not to imagine
a purple elephant, but now all you’re thinking about is a purple elephant.
Then again, you often have to practice thinking about something you want to remember, like
your credit card number.
So doing the opposite -- practicing not thinking about it, or making sure to think about other
things -- might make you better at avoiding the memory.
If you avoid it often enough, maybe eventually you’ll forget it.
Which does seem to work.
In 2012, one group of American and British researchers published a study in the Journal
of Neuroscience where they monitored the brains of 18 females while they did some memory tests.
They used fMRI to measure blood flow in the brain -- more blood in one area generally
means it’s more active.
They found that the subjects were better at forgetting pairs of words they’d purposely
tried not to think about than pairs of words they wanted to remember.
Which seems to support the idea that we do have some level of control over what we remember.
The researchers also found that when they were trying to remember a word pair, they
showed more activity in the hippocampus, a region of the brain that helps with turning
short term memories into long term memories..
And when they’d completely forgotten the word pair, the hippocampus didn't show any
change in activity at all.
But when the subjects were trying to forget a word pair, they showed less activity in
the hippocampus, but more activity in another part of the brain that’s associated with
the hippocampus, known as the dorsolateral prefrontal cortex, or DLPFC.
It’s involved in managing temporary memories, but it’s also important for planning.
So this region could be involved in the active forgetting process, and it’s probably a
good place to look for ways to control that process.
There are a couple of things to keep in mind about this study, though:
First, 18 subjects is… not a lot of subjects. This needs to be tested more before we can
call it conclusive.
Second, words are just that -- words.
They’re nowhere near as complex as actual memories, so we don’t know how much of what
the researchers found applies to real life.
Another study, published in 2013 in the Journal of Experimental Psychology, tried to fix some
of those issues by studying personal memories.
There were 60 subjects this time, though they were all college students.
The students were told to associate certain pairs of words with happy or unhappy memories,
and the researchers recorded how many details of those memories they could remember.
Then, once the subjects had memorized which memory went with each word pair, the team
showed them the word pairs and either told them to actively think about the memory, or
to try not to think about it.
Afterward, the students were asked to describe the details of the memories again -- but they
couldn’t remember as much from the memories they’d tried to forget.
They didn’t forget the entire event or anything, but that might have something to do with the
fact that the experiment only lasted a week.
So we know that actively trying to forget things like word pairs involves more activity
in certain regions of the brain and less activity in others.
We also know that similar techniques work if you want to forget more complex memories,
like of events.
The next step would be to try to identify some of the proteins -- and the genes that
control them -- involved in active forgetting.
Which is why some researchers are studying the genes that control memory using a type
of tiny worm known as C. elegans.
In 2014, a group of Swiss and Hungarian researchers published the results of a study in the journal
Cell.
They’d trained different groups of worms to understand that if they crawled toward
or away from a particular smell, they would find food.
But some of the worms had a particular gene, known as musashi, turned off. And they remembered
the smell cue longer than the rest of the worms.
That makes sense, because musashi controls how cells make a protein that helps with reshaping
the paths neurons use to transmit information.
So, the thinking goes, if the pathways can’t change, the worms don't forget.
Then, in a study published in the journal Nature Communications in August, a team of
neuroscientists tried to block the emotions associated with rat memories by interfering
with certain genes.
They based their experiment on the idea that sometimes you - or research rats - might first
learn to fear something, like taking a particularly difficult test.
But say the next time you take a test, it turns out to be super easy for you.
...And the next one, and the next.
Eventually, you might even forget that you used to be scared of taking tests -- that
is, until you sit down for the final exam and the first question is so complicated that
you don’t even understand what the teacher’s asking.
But what if you’d turned off the genes that control the processes in your brain that remind
you to be afraid of the test?
The researchers tried to figure that out by studying rats, who were placed in a cage and
given a small foot shock.
They were taken out of the cage, but then put back --this time without any foot shocks.
Basically, they were training the rats not to be afraid anymore.
Then, the team gave some of the rats a drug that would limit the activity of a gene called
Arc, which is associated with long-term memory formation.
When these rats were given another, small foot shock -- enough to trigger the memory
of fear, but not enough to teach them to be afraid all over again -- they still weren’t
showing signs of fear.
We humans share some of our genes with worms and rats -- we have our own versions of musashi
and Arc, for example. So these types of studies could eventually help researchers build a
forget button for humans, too.
Knowing what genes are important for a process - whether it be forgetting a memory or increasing
your risk of developing a disease - is useful for scientists trying to understand how to
change that process.
So with more research, we might eventually learn how to control which memories we forget.
But if you could permanently, completely forget certain memories, would you actually want to?
Right now, even the most advanced forgetting techniques can’t completely eliminate a
memory -- they just help you remember fewer details or associate the memory with less
intense emotions.
But if we could perfect our ability to force ourselves to forget, there would be a lot
of ethical and moral questions to address.
For all we know, forgetting a memory would change who you are as a person.
And purposefully forgetting a crime you committed -- or witnessed -- would be a big problem
for the legal system.
So, even if we can reliably make ourselves to forget, who gets to decide what memories
we remember?
What do you think? Let us know in the comments below.
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