Have you ever envied Kate Winslet’s character in the “Eternal Sunshine of the Spotless Mind”? Have you ever wished that you could erase memories of a nasty ex just by pushing a button? (I sure did after one of my exes told me that trees have souls whereas I do not) Or that you could bring an elusive memory back into your head? (I bet everyone who has ever written an exam sure did). Basically: Would you like to manipulate memory?
First, let me tell you a little bit about memory itself. A lot of people understand memory as a huge bag full of song lyrics, embarrassing moments from years ago and first halves of jokes. You put it in, time passes, you take it out, brush away the dust, ready to go as good as new. Now sorry to break it down to you but that is very incorrect. Memories are a brain-wide process. They are dynamic and fragile; they are transformed by experience and prone to interferences. Memories are not files stored in the drawer, but rather delicate plants which needs maintenance and care in order to stay with you for a long time (this brilliant metaphor should answer the question of why I'm not writing poems or fiction).
So let's see,
1. How are memories created and stored in the brain?
When you experience a thing -- say getting hugged by David Bowie (that was the first thing my brain provided me with when I asked it for an example of a meaningful significant event, sorry) -- your brain encodes a lot of information: The smell of Bowie's perfume, the look in his eyes, the touch of his stage costume, furniture of the backstage room you're in. These incoming sensory signals are sent down to hippocampus, a sea-horse like structure deep in the brain which is responsible for creating new memories. Hippocampus links these pieces of information together, making a coherent episode out of them ("The time I met Bowie").
As scientists call it, the memory gets consolidated. As you recall this event, the whole neural ensemble belonging to the memory gets reactivated and the connections between the neurons (which are called synapses in the world of science) associated with the memory become stable. So in the end if you hear a Celine Dion ballad, you are likely to remember your first kiss at the summer camp disco (or at least I am).
Recently, MIT researchers has made some impressive progress in the field of memory research: They showed how specific memories are stored in specific brain cells and activating just a small cluster of cells belonging to a memory is enough to make the subject (a mouse) recall the whole thing. It finally proved that a memory engram is a physical, rather than a conceptual term. It opens the door for so many possible future (very far in the future) applications: Erasing memories, enhancing memories, changing memories... Which brings us to the next point.
2. How can memory be manipulated?
As I mentioned before, memories are unstable. If you don't reactivate the memory trace often enough it becomes weaker and your memory fades. Not only that, every time you do revisit a memory it becomes vulnerable. This process is called reconsolidation. Think of it like that: Every time the memory trace is reactivated the memory becomes like molten glass which can be changed a bit before turning back to solid. Memory is an act of creation, you guys.
Elizabeth Loftus, a big name in the false memories research, spent decades to see how our memories change by our later experiences. She found that various post-event information, e.g. suggestive questions, can alter our memories of an event. Say you witnessed a car crash. Later, if you are asked “About how fast were the cars going when they hit each other?” you are likely to give a lower speed estimate than after being asked “About how fast were the cars going when they smashed into each other?”. So... Maybe we shouldn't rely on the witness testimony much, huh?
(If you want to know more about her research check out her TED Talk):
Or say you wanna forget your weird ex. One possibility is tequila. Another way would be to disturb the reconsolidation process on the cellular level. At least, it worked for mice: A brain region playing a role in re-consolidation was optogenetically (don't know what this word means? check my previous post on this topic!) silenced in mice in the exact moment they were recalling a memory of an electric shock hitting them in a specific room. Next day a lot of the manipulated mice didn't seem to recall anything bad happened in this room whatsoever, carelessly strolling around. Seems like preventing a contextual memory from being re-stabilized can help to erase it. Hello, future PTSD treatment!
There is another potential way to erase a memory. Remember how memories are nothing more but a cluster of neurons strongly connected in a particular way? A pretty cool study by Nabavi and colleagues showed how a memory can be erased and restored again just by optogenetically weakening and strengthening the connections between neurons constituting this memory. If this isn't exciting I don't know what is! Goodbye, weird ex and your damn soul trees!
Speaking of PTSD: if erasing seems too extreme there is another way. Seems like it's possible to change the emotional memory of an event. Redondo and his team managed to unplug a memory of the context from the emotion associated with it (I got to sniff a female in this room! What a good and emotionally pleasant room this is!) and replug this contextual memory to another emotion (Oh no! Something bad happened in the room! I better freeze in the corner). Sorry, forgot to mention, participants were mice, not humans. It was done by manipulating connections between hippocampus, where as we already know the contextual information about the event is stored, and amygdala, where the emotional component of the memory is maintained. So maybe soon it will be possible to unplug the sight of a battlefield from the panic and terror in the veterans? Maybe instead they will associate it with a feeling of calmness and zen? Or at least with some neutral emotion? I damn hope so!
Okay, so much about forgetting and changing, what about enhancing? Well, this technology we talked about just now might come in handy for say, helping Alzheimer patients by strenhghtening the weakened synapses of a specific memory engram (Make your synapses great again! Sorry). Another way to become a memory super-human would be to stimulate your brain with magnetic fields (short journey to the neuroscientific methods: TMS -- transcranial magnetic stimulation = magnetic fields that pass through your skull and produce electric currents there. Harmless, believe it or not!). Voss and team used TMS to enhance the activity in a circuit between hippocampus and neocortex which is thought to be essential for memory. After a few days of stimulation the participants scored much better in memory tasks! Think of it like this: TMS improved the road between these two locations, but didn't change the type of vehicles travelling on them (meaning that TMS isn't specific enough to only enhance specific memories).
The last but not least (and in fact my favorite) example of manipulating memory is implanting false memories. I talked about it before here so won't waste space on it in this post. But ohmigod, making a mouse believe something that never actually happened?? FUTURE IS HERE, PEOPLE. IT IS HERE.
Thanks for staying with me! Next time I'm thinking of making some brain 101 post, so that later I can use all the fancy terms without you being confused :)
The illustrations for this post were made by my wonderful friend and talented artist Toma. Check out her art at http://tomathespook.tumblr.com!
Links to the mentioned studies for brave and adventurous: