MIT discovers the location of memories: Individual neurons

http://www.extremetech.com/extreme/123485-mit-discovers-the-location-of-memories-individual-neurons

by mrsebastian • 14 years ago

341 120 14 years ago

octotoad• 14 years ago

'The mice “quickly entered a defensive, immobile crouch,” strongly suggesting the fear memory was being recalled.'

Yes, possibly. Or maybe it had something to do with the hole that had been drilled in their skulls and the frickin' laser beams being fired at their brains. Pretty cool stuff though.

relix• 14 years ago

They obviously controlled for that.

cmaxwell• 14 years ago

hahaha

I came here to post that... too late.

seclorum2• 14 years ago

They didn't 'discover the location of memories', they simply discovered that they can trigger a reaction that looks similar to that of the original incident by focusing energy on parts of a mouse brain that were actively stimulated during the incident.

This is Pavlovs dog with optics, not revolutionary science.

GiraffeNecktie• 14 years ago

I don't understand your reference to Pavlov's dog, it's more comparable to Penfield's work with stimulation of specific points of the brain. Also the ExtremeTech headline is a bit misleading. The related MIT article is a little more clear that this involves memories in a small cluster of neurons, not one memory per neuron as is implied by the heading above. http://www.mit.edu/newsoffice/2012/conjuring-memories-artifi...

mrsebastian4• 14 years ago

Yea -- sorry, I mention later that it's a cluster, but I will update the first paragraph to mention that it's a cluster, not single neurons.

bburns2• 14 years ago

Not revolutionary? It's a relatively small step from here to mapping out the neural pathways which trigger specific memories. If we can figure out those underlying structures, we can hopefully learn how to read and modify them.

I need my Matrix-style brain downloads!

drbawb• 14 years ago

More importantly imagine how many people this could help!

There's a bit of ethics involved, but what if we could simply remove traumatic memories to treat psychological disorders?

Plus, yeah, plugging in to learn karate would be pretty awesome.

espeed• 14 years ago

MIT scientist Sebastian Seung talked about this possibility in his 2010 TED talk, "I am my connectome" (http://www.ted.com/talks/sebastian_seung.html).

jules3• 14 years ago

The data doesn't warrant the title of this post. Even if a single neuron is responsible for triggering a memory (which is hard to say based on mice in the first place), it doesn't follow that the information is stored in the neuron. As an analogy, if we erase a specific bit in memory, whole parts can become unreadable. For example imagine changing a bit in a pointer. That doesn't mean that all of the information was stored in that bit.

amalag• 14 years ago

I agree with this. Because of the brain's ability to access things which are not exactly constrained to it's physicality, I think the brain acts as a type of radio and tunes into memories. Not exactly sure how they are stored.

arethuza• 14 years ago

"the brain's ability to access things which are not exactly constrained to it's physicality"

What does that mean? Not being snarky, just interested.

mrsebastian4• 14 years ago

There's a very strong urge to believe that the brain "tunes" into some kind of non-meatspace realm (spiritual, quantum, etc.)

Fairly sure that it'll turn out that it just depends on the massive complexity of neuron/synapse connections, though.

But then you think of concepts like 'group psyche', and twins that are separated from birth but share the same thoughts/feelings over a distance...

Hopefully science will get to the bottom of it soon :)

jules3• 14 years ago

A more down to earth explanation on where the information is stored, if not in the neuron, would be other neurons that the neuron is connected to (and neurons they are connected to, etc.). In fact it seems fairly likely that information in the brain is just stored in the strength of synaptic connections. Just like in the computer memory case, really. Even though a complete data structure might is not stored in a single bit, all data inside it is eventually stored in bits and not in some magical realm "outside of physicality of the computer".

dacilselig• 14 years ago

Can you cite something? Did you come up with this on your own or did you read it somewhere?

irahul• 14 years ago

> Because of the brain's ability to access things which are not exactly constrained to it's physicality,

Philosophy and spirituality aren't science. Do you have any citations for brain's metaphysical abilities? Unless proven to be true, personal anecdotes and old wive tales aren't valid data points. Apart from it, I haven't read anything about brain transcending the physical.

There is a lot of unknown viz. we don't know what constitutes consciousness, but that doesn't mean it can be attributed to metaphysical. Physical or metaphysical, you need to know for sure - till then, it's "no man's land".

polyfractal5• 14 years ago

I came storming into this thread ready to post exactly your statement. The title is way over-blowing the situation. There are so many caveats here its hard to do it justice.

First, they found single neurons which trigger memory, a far cry from containing the entire memory. Think of them as gateways to a house. A gate does not hold the house, but it does let you access the house.

Second, they didn't remove any neurons (from my brief skimming of the press release at MIT[1], I don't have time to read the paper now). There is almost a 100% chance that there is a large subset of neurons which will trigger the same memory. Which means this house has a lot of gates. Nothing is becoming "unreadable" here.

Third, this trick of using optogenetics to trigger a memory has been shown several times over already. Here it was reported by Boyden and Hausser in 2009 [2]. Presumably this piece is being reported because it was performed by Tonegawa's lab. Not discounting the research, there is likely a lot of advancement on the underlying science, the optogenetics (which are undoubtedly being borrowed from Boyden's lab across the street) and the understanding of mechanism...but it isn't new.

[1] http://www.mit.edu/newsoffice/2012/conjuring-memories-artifi...

[2] http://www.technologyreview.com/biomedicine/23767/

jules3• 14 years ago

Exactly. The function of a neuron is to trigger other neurons. If you removed a neuron, but manually triggered exactly the neurons that the removed neuron would have triggered, it is to be expected that the same memory would be recalled.

Obviously, this argument breaks down at some point, since by induction we could remove 100% of the neurons and manually trigger the axons to the muscles that would have been triggered by triggering the single neuron in the intact brain. This would give the same observable behavior, but it is not clear whether the same experience would be had. But this is getting into the area of consciousness, which is something that nobody understands (yet).

stiff2• 14 years ago

They haven't just "found single neurons which trigger memory". They found the only neurons that were active while experiencing a specific situation and memorizing it and they managed to show that activating only those neurons is enough to trigger a reminscence of the very same experience. You cannot say some other neurons would trigger the same memory, because nothing changed about those neurons during "generating" this memory (under the assumptions science currently holds about the brain), so they cannot store it.

cdcox2• 14 years ago

Boyden and Hausser gave a talk claiming they can do it in 2009. However, I cannot find a citation claiming they ever published this work. As it goes in the field, first to publish is more important than first to claim.

ilaksh• 14 years ago

I was watching Jeff Hawkin's thing yesterday and he kept talking about sparse distribution something. I didn't get most of it but it didn't seem to square with the headline's emphasis on individual neurons.

http://www.youtube.com/watch?v=48r-IeYOvG4

hippich• 14 years ago

I always was under impression that there are no memories as we think about photographs, but rather state of the brain is one whole memory system, which react to external signals accordingly to previously "memorized" signals.

As I understand, that they just found a way to excite particular small part of the brain which triggered reaction without external signaling. I.e. bypassing all intermediate parts (external sensors, nerves, other neurons, etc). I.e. it is more like to directly feed engine with gas and electricity to create a spark to make it revolve completely skipping engine control unit, ignition key, clutch pedal, fuel pump.

And when they refer to memory loss due dying neuron, this is more like part of circuit is removed which supposed to give certain reaction to certain signals, not like "rm /home/user/file.txt" with the rest left in place. So I do not believe thing similar to MiB is possible with this knowledge.

bburns2• 14 years ago

There's an obligatory Eternal Sunshine of the Spotless Mind reference to be made here...

debacle2• 14 years ago

There was an Eternal Sunshine of the Spotless Mind reference in the article. You should have read it.

bigiain4• 14 years ago

I can't help but think that what they've discovered is some meatspace equivalent to the hash key or an index key to a memory. By "turning it on or off" you can lose or find a whole table row or hash value, but surely a "single neuron" can't "store" a generalised "memory".

loceng• 14 years ago

I'd see it as the keycode / directions / a path to connecting all of the pieces; At what level all of the pieces are stored at (biological/physical in brain, in subtle energies, other?), who knows?

snippyhollow2• 14 years ago

A neuron "could" store a generalized memory (the amount of information it stores is gigantic, w/o pendantically considered the DNA). However, it's more complex than that (there are many types of memories and many means of retrieval). Basically, memories are sets of synaptic connections, and a neuron has many synapses (average ~7,000 synaptic connections/neuron to multiply by our 10^11 neurons/brain). As you said, it may be a "key", but it should be seen more like the memory _is_ a complete list of hashes. Not {"key": memory} but {"key1": {"key2": {"key3": {...} } }, {...}, {...}, ...} and the set of {key1..keyN} is the memory. So if you removed whichever keyI in the middle, you lose the information. (That's not really true because there is high redundancy, but there are keys/synapses/nodes less redundant than others. The fact is, they don't fire on only "one" neuron, they fire at a very precise region but the light still goes through a population of neurons.)

bigiain4• 14 years ago

Fascinating, thanks! Have you got some links or keyphrases I should feed Google or Wikipedia to learn more (at a "curious but not neuro-science trained dilettante" level of understanding)?

bostonpete• 14 years ago

This complexity make my head hurt. Who created this mess of complexity anyways without leaving so much as a code comment or design document to help us sort this all out? Intelligent design my ass.

troyastorino2• 14 years ago

The laser can't be aimed at an individual neuron; it is aimed at a cluster of neurons. Besides, activating a single neuron will strongly activate the neurons it has strong synaptic connections to. The key here is that an individual cluster of neurons is directly correlated with an individual memory.

polyfractal5• 14 years ago

I don't know if it was used in this paper, but you can obtain single-neuron targeting using two-photon microscopy.

aidos• 14 years ago

There was a Ted talk some time ago about the work on optogenetics (in fruit flies I think) http://www.ted.com/talks/gero_miesenboeck.html

debacle2• 14 years ago

I think this has been overhyped just a bit. I realize that a discovery of this nature is a big deal, but it's not what journalists are making it out to be.

mistercow• 14 years ago

>MIT researchers have shown, for the first time ever, that memories are stored in specific brain cells. By triggering a single neuron, the researchers were able to force the subject to recall a specific memory. By removing this neuron, the subject would lose that memory.

That's incredibly poor reasoning. Using the same logic, I can "show, for the first time ever" that C structures are stored in individual memory pointers.

kghose• 14 years ago

If you are interested in this sort of thing (memory storage in the brain, recall etc.) you might be interested in Wilder Penfield's work. (e.g. http://primal-page.com/penfield.htm)

danmaz74• 14 years ago

I read the MIT news piece and didn't find any reference to the removal of a neuron that would eliminate the memory. Was that in a longer research paper?

mechanical_fish2• 14 years ago

OMG, it's the ultimate mechanical_fish pet peeve collection! TL;DR: I rant.

ONE: I can't find the citation of the scientific paper on ExtremeTech. (Let alone a link. Who would dare to dream of a link?) They do refer obliquely to "the paper" once. (What paper?)

And they link to MIT's press office, whose brand is really solid, so everything they write is almost like science! And there you can skim the article twice and finally spot the citation:

Susumu Tonegawa, the Picower Professor of Biology and Neuroscience at MIT and lead author of the study reported online today in the journal Nature.

Okay, gotta go find an online Nature subscription to find out what's going on. There's an hour of my day spoken for. At least they're trying to ensure I get some exercise.

Why is the actual journal article important? Just look at this thread here on HN. We have people doubting all sorts of things, but these may well be things that are addressed in the actual work. The content of the popular articles means very little: They leave out most of the details. The details matter. The whole point of this study is to try and tease out more details.)

TWO: But, wait, there's more. I first tried to read ExtremeTech on an iPad (original edition). The article popped up in one of those insufferable iPad-only JS-powered "mobile editions" with Swiping Action. Unfortunately, there was only the first page of the article. It cut off in midsentence. I tried pressing the giant button marked "Next" on the right side of the screen. I got a big white screen. I flailed around with my fingers. A completely different article eventually rendered itself. I flailed around with my fingers some more. Eventually the original article reappeared, still incomplete. Fortunately, one more roundtrip to the next article and back and I finally got the whole thing to render.

Then I pressed the back button and everything seemed to hang. I closed the browser window and thanked the gods for my escape.

Why on earth do publications use these broken things, when simple web pages render so nicely on the iPad? The site does have something like a dozen tracking cookies on it; does this imply that they have data showing that swipability is so important that it doesn't even have to work in order to attract more ad impressions/clicks/Tweets/whatever? Or does it merely suggest that they are so busy struggling with glass-cockpit syndrome that they can't perceive that their site is broken on the iPad?

bigiain4• 14 years ago

Cynical-me thinks "screwed up page rendering and swiping just achieved 4times more page views to claim to advertisers - mission accomplished, goals met!"

obituary_latte• 14 years ago

It crashed my browser too. Twice. Big tower-computer-thingy with a couple of meg-joules of RAM and Pewter web browser.

Thankfully, I was able to spot the problem after visiting the page with my lawnmower: http://i.imgur.com/4jnGv.png

mrsebastian4• 14 years ago

I will add a link to the paper itself; sorry about making you jump through hoops.

polyfractal5• 14 years ago

Hey, props for responding to criticism! As a (now ex-)neurobiologist, it's maddening when journalists don't cite the paper they talk about. I helped start ResearchBlogging.org way back in the day to help fight this very problem.

If I may make a suggestion: wrap your citations in OpenURL COinS format. ResearchBlogging.org provides this functionality automatically, but you can do it yourself too. It provides a lot of useful meta-data, citation information and the ability for plugins to interact intelligently with the web-page

[1]http://ocoins.info/

mechanical_fish2• 14 years ago

Thanks so much. It's awesome to see this practice start to change. At this rate maybe I'll soon be able to control my pet peeve with medicine.

Alex39177• 14 years ago

"Just look at this thread here on HN. We have people doubting all sorts of things, but these may well be things that are addressed in the actual work."

Presumably if MIT had actually discovered the nature of consciousness we wouldn't be reading about it in some tabloid. The research may be less bad than the article suggests, but there's no way it's as good as the article suggests either.

onemoreact3• 14 years ago

The fact that consciousness runs on neurons is hardly breaking news.

troyastorino2• 14 years ago

Studies published in Nature typically don't have bad science...

ilitirit• 14 years ago

> The question now, though, is how memories are actually encoded — can we programmatically create new memories and thus learn entire subjects by inserting a laser into our brain?

That's a pretty scary area of technology. I hope that as a civilization we will become responsible enough to use that before we discover how.

joshaidan• 14 years ago

Maybe this means we can finally build a machine like the one in the matrix that lets us bootstrap our brains with kungfu.

But more importantly, I think the most significant result of this research, should even a bit of it prove to be true, is the possibility that it could help us understand, and maybe even prevent dementia. That's exciting!

carbocation2• 14 years ago

Sadly, and I mean very sadly, this doesn't mean that. =)

The reason it doesn't mean that is that they are triggering naturally-programmed neurons via light. They are not programming them via light.

mckoss• 14 years ago

I wish I could block all extremetech stories from My HN feed. The are universally overhyped, never the original source, often draw unjustified conclusions, and are a pain to read (at least on an iPad - they use a non standard interface and pop overs).

aw3c2• 14 years ago

Maybe some "flag this" concensus would work.

j45• 14 years ago

I wonder if by deleting not so nice memories (i'm guessing that would be one of the first applications) the person will continue to make the same decisions over and over, because they might not remember them and keep re-experiencing (and learning) repeatedly?

carbocation2• 14 years ago

The journal article can be found here: http://www.nature.com/nature/journal/vnfv/ncurrent/full/natu...

It doesn't seem to claim that an individual neuron is the location of a memory, but rather that triggering a small number of specific neurons is necessary and sufficient to cause the behavior that would be consistent with the recall of a particular fearful memory in mice, when optogenetically triggered.

In other words, they labeled some neurons with an optogenetic receptor during fear conditioning. Then, thanks to the optogenetic labeling they previously did, they were able to activate this receptor (using light) in a totally different context (one that didn't normally elicit the freezing response associated with mouse fear). When they did so, the mouse exhibited the freezing response. When they ablate these neurons, there is no fear response. The conclusion is that these neurons are necessary and sufficient to encode the fear memory.

Caveat lector: my summary is based on the abstract so I am just parroting what they have concluded; I haven't read the paper's methods and results for myself. Also, this is the "near-final" version published in advance online today. It may change for final publication.

stefantalpalaru• 14 years ago

The Nature abstract is about a "population of neurons" and triggering a memory related behavior while the extremetech article talks about "specific brain cells" and memory storage.

Nothing to see here, move along.

stiff2• 14 years ago

Here is a simple explanation of the experiment:

1. The set of neurons that was active only during learning was determined.

2. The genes activated in those neurons were determined.

3. Genetic engineering was done to make the activation of those genes always happen in conjunction with activation of the gene being responsible for the neuron becoming sensitive to light.

4. The mouse was put through a learning experience, during which the small group of neurons affected became sensitive to light.

5. Via stimulating those neurons with light, the experience was reproduced in the mouse in a completely different environment (so the comparisions to Pavlov are not justified).

In this way the abstract concept of a memory and of the process of remembering something was related very closely to a specific physical phenomena. Even the methods used to make the experiment are interesting by themselves (at least for a lay person) and I think you cannot easily dismiss the importance of this discovery as some people do here. Please read the article here to get a better picture:

http://www.mit.edu/newsoffice/2012/conjuring-memories-artifi...

Craiggybear2• 14 years ago

I don't believe a word of this. It isn't proof of any such a process. This to me appears as inappropriate reductionism.

The brain is highly volatile both chemically and physically and is changing minute by minute. The notion that a memory belongs to a single group or cluster of neurons is absurd. They are constantly being reordered and reprioritised and changed throughout the lifetime of the animal. And being lost due to chemical damage and the effects of ageing and free radicals.

The nature of memory and conciousness isn't just the physical existence of neurons. Who you are is more than the sum of the parts.

The mind is also as much a process of the body -- your conciousness and mind grows within it from birth and a large part of who you are is as much a product of that, its hormones and its metabolic chemistry as anything that resides solely between the ears alone.

wtvanhest• 14 years ago

Off topic: I live across the river from MIT. I work in asset management and worked for an angel investment fund. I'm working on a startup at night. If you live in Boston and want to meet for coffee email me.

I'll meet anyone from HN, even if you just want some career advice for working in asset management or just want to talk about random stuff.

My email address is my hn username at gmail.

deadmike• 14 years ago

"The mice 'quickly entered a defensive, immobile crouch,' strongly suggesting the fear memory was being recalled."

Perhaps the defensive, immobile crouch had something to do with having a hole drilled through their skull and a laser shined through said hole?

cdcox2• 14 years ago

That title is incorrect. These researchers did not stimulate one neuron to activate one memory. They stimulated a group of neurons in one region using a fiber optic.

I'll go through the experiment for those who don't really get the write up. Quick background:

0. Neurons are specialized cells in your brain, their firing is the basis of cognition. Neurons that fire strongly together tend to get linked. Not all your neurons are firing all at once. Not all neurons participate in a memory, but a large collection (0.1-4% depending on brain region) are used for each memory. (at least in naive mice) Memories are highly distributed across brain regions and within brain regions.

1. There is a gene 'cFos' that turns on in neurons that undergo activity. It is very short lasting, about an hour, and then it is back down. It is very cell specific, only cells used have been activated will show this gene.

2. There is a genetically inducable protein you can put in cells so that when you shine them with light they will start firing.

3. Anything genetically inducible can have a tag added that will make it impossible to induce when an animal is on a specific drug. (We'll call it Dox.)

The researchers made it so that when cFos is activated, it will transcribe the inducible light activated channel. But, it will only do this when the animal isn't on Dox. So they took the animal off Dox, exposed it to fear conditioning (they shocked it in a unique box), then put it back on Dox. So only the cells that were active during the fear conditioning will be turn on when they shine light.

They then put the animal in a new box and shined light, and the animal froze. (A sign it was afraid) They concluded that activating cells that had been active during the storing of the memory can 'reactivate' the memory, even out of it's context.

Of course there are a few major problems with this. The region of the brain they worked in is a relatively minor area of the brain. They admit in the course of the paper that each cell is used to store many memories. (They claim the assembly of cells activate the memory? But they never bother testing this.) Their firing pattern is far from physiological. The mice who underwent this 'memory reactivation' did not freeze as much as mice in normal fear conditioning and did not seem to learn the 'reactivated memory' at all. (Though again they didn't really bother testing this.) Normal fear-memory is learned quite well. This is a very preliminary but very important study in the field. It will be interesting to see how they follow this up.

Also, the Npas4 stuff is completely irrelevant to this article. There are countless markers that when 'knocked out' make it impossible to store memory.

Also here is a (paywalled) link to the paper:http://www.nature.com/nature/journal/vnfv/ncurrent/full/natu...

Here is a link to another (paywalled) paper which came out today which did almost the same thing and say almost opposite results (the details explain this oddity): http://www.sciencemag.org/content/335/6075/1513.full?rss=1

Here is a (paywalled) more layperson write up to the second article: http://www.sciencemag.org/content/335/6075/1455.full

zerostar07• 14 years ago

Impressive as this may sound this is not the first study of its kind. Studies since 2009 (mentioned in the abstract) in the amygdala have been able to direct and inactivate fear memories in a reversible manner via optogenetics again (see http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2844777/) . In these studies killing as much as 15% of the cells did not erase the memory, indicating that it's ensembles, not single neurons that encode fear memories.

To complicate the picture even more, each neuron is part of more than one memory engrams, and memories are stored in synaptic connections which are formed in the vast dendritic trees of neurons. So you have a very sparse and reduntant encoding of this associative memory.

Finally, note that both the amygdala and the hippocampus are very old structures so we don't know if the same processes take place in the neocortex (although it's likely so).

I don't mean to belittle the article, but it's mostly proof of concept if you have followed the relative literature. Tonegawa's lab had some even more fascinating papers published recently that probe the process of memory encoding to the level of single dendrites.

PaulGrinsBig• 14 years ago

This article sucks, the quality of online journalism has taken a new low...there are no citations...just rambling that eventually one finds to be a total misunderstanding of the results and of science in general...ahhhh...

isa• 14 years ago

Besides the fact that the scientists used trauma to retrieve their data, what a beautiful notion: collecting a memory at the tip of every neuron.

holeinskull• 14 years ago

  This is a expected  response and perhaps has nothing to do with remembering.

jpwagner• 14 years ago

http://blogs.nature.com/actionpotential/2012/03/fear-of-the-...

zallarak• 14 years ago

My brother, who is studying in medical school right now pointed this out to me: "the whole time i was reading this though, i was bothered by what usually bothers me about studies regarding the mechanics of the brain, which is that we dont know our measures of "activation" are sufficient for determining a causal relationship between activation of certain neurons and the recall of certain memories."

rsanchez1• 14 years ago

I always take these with a grain of salt. One day a study comes out saying that memories are not stored in a specific location, that scientists can cut out large portions of mice brain and the mice will retain memories, and the next day a study comes out that specific memories can be created or destroyed with specific neurons.

MIT discovers the location of memories: Individual neurons

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