Script writer for YouTube channel SciShow.
Thinking about happy memories might make you feel happy. But not all memories are pleasant. Some things are just embarrassing, like that time you ordered red wine with fish on a date. 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 telephone 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.
This 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 women 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 2015, a team of neuroscientists tried to block the emotions associated with rats’ 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 studied rats to try to figure that out. Researchers placed rats in a cage and gave them a small foot shock. They were taken out of the cage, but then put back --this time without any foot shocks. Basically, the researchers 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.
If we can reliably make ourselves to forget, who gets to decide what memories we remember?
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