How much can one mind hold?
December 14, 2007 12:55 PM   Subscribe

Is there a limit to the human brain's storage capacity?

Is it possible for you to literally "run out of room in your head"?
posted by trokair to Education (24 answers total) 6 users marked this as a favorite
 
Of course it is limited, but no one knows what the limit is, and it seems to be high enough so that no one ever runs into the limit.
posted by Steven C. Den Beste at 12:57 PM on December 14, 2007


You could set an upper limit just based on the maximum information density of matter. Obviously the brain's capacity would be lower, but it's a good start.
posted by nervestaple at 1:00 PM on December 14, 2007


"Human brain has estimated storage capacity of 1.25e12 bytes."
http://tinyurl.com/36cl7s
posted by ofthestrait at 1:04 PM on December 14, 2007


And according to google,

1.25e12 bytes = 1,164.15322 gigabytes

So just over a terabyte.
posted by ofthestrait at 1:05 PM on December 14, 2007


Well, the first thing that comes to mind are savants, and some of them seem to have an increased memory capacity, at least compared to us normal humans.

As I understand it, memory is closely linked to how important the nugget of information is. Which is why, for example, I can't remember which desk I sat in during the 2nd grade, because it's no longer relevant to me. Perhaps somebody with a better memory than me might tend to think that everything is important, and therefore, has a better memory than I do.

It's an interesting thought.

This episode of Radio Lab might help.
posted by kpmcguire at 1:12 PM on December 14, 2007


Unlike a computer the brain can "rewire" itself to store more information and to cull unused information. As it does this it automatically makes more efficient use of it's stored memories.
posted by JJ86 at 1:16 PM on December 14, 2007


Assuming one lived long enough to do so, what would it be like to reach the limit? Would the saturation manifest as an inability to transfer short term data to storage (like the anterograde amnesia in Memento), or would older memories fade in favor of new ones?
posted by Iridic at 1:16 PM on December 14, 2007


Best answer: It is hard to measure memory because the brain does not store memory in the same way as anything else we know. The abundance of research showing the effects of false memory (a recent one introduced fabricated photos from the past and asked people if they remembered it , in a nutshell they were fooled into believing it was a memory).

One can look to the mathematical treatment of information density such as Kolmogorov complexity, which gives an idea of how hard it is to accurately quantify what memory is. My guess is our memory is not as robust as we would expect and we use a variety of highly efficient heuristics to store and recall memories.

The savant case is interesting, but I think it shows the computational and storage (if we wish to put it in those terms) of social interaction and emotional intelligence as being much, much higher than we realize. The crude idea being that savants such as the one depicted in the rain man can't function socially on a normal level and have a lot of extra capacity to do amazing feats. That's very, very crude but I think the idea remains that we just don't know.
posted by geoff. at 1:21 PM on December 14, 2007


Best answer: I think its naive to model the brain as a disk drive. We have no idea how the brain stores information.

The information storage capacity could be much greater, in the Shannon sense, depending on how the brain "compresses" information. Apparently there's a lot of associativity involved. And this compression cant' simply be looked at as pure information compression in the WinZip sense since the brain may use information within itself or in the physical environment to "decompress" this information most effectively.

A related example is the storage capacity of DNA. Its not that much from the "disk drive" analogy. But apparently, it can be "decoded" by proteins (with their own external information content) into an entire human organism - including the brain. So, clearly there's a lot more data there than just counting the number of bits and bytes.
posted by vacapinta at 1:23 PM on December 14, 2007 [2 favorites]


human memory != computer memory.

Sorry.
posted by zpousman at 1:47 PM on December 14, 2007


Best answer: Note: all of this is from some AI courses focusing on neurology in college that could charitably be described as 'theoretical neurotopology' - ie, we don't know for certain this is how the brain works, but it's a good best guess based on what we're seeing in neurological studies and in artificial neural networks.

To literally run out of room, no - the human brain has what you might call a low-level background 'noise' that is constantly slowly decoupling existing dendritic connections. Thinking about a memory causes the connections that correspond to that memory to be refreshed. Not thinking about it long enough allows the connection to 'unravel' and the space can be used for something else.

However, neural activity in the brain generally entails some level of spillover - ie, thinking about a topic/memory that is one location of the brain may cause activation/minor refreshing of topics that are adjacent at the neurotopological level. Big caveat: while there's probably a fair amount of correlation between semantic proximity (ie cars and trucks) and neural proximity, medical literature concerning people with brain damage already demonstrates that this mapping is far from 1:1.

You might also be wondering 'well if the brain can't run out of room, why can't old people learn new skills as easily as younger people?' The reason for this is that the core neural pathways of a person's reasoning become extremely firmly entrenched over a lifetime of use - like deep wagon ruts in a dirt road. It gets harder and harder to branch out the more your core reasoning/consciousness 'loop' is reinforced. It's reasonable to assume that different people have core neural pathways that allow for greater or lesser amounts of flexibility, but for most of us neurotopological plasticity begins to decay starting around your late 20s.

Generally speaking, the best things you can do to keep up that plasticity and to spark neurogenesis is to learn many semi-related topics in-depth. Do you know UNIX? Good, start learning low-level networking and DNS. Do you know C++ programming? Good, branch out into derived languages like Java. Do you know macroeconomics? Good, study microeconomics or foreign relations. Learn those topics well enough to get a true indepth understanding of their knowledge infrastructure - you don't have to be an expert, but you should understand all the 'whys' of the topic's inner logic.

Nutritional factors and genetic predisposition for slow accumulation of certain proteins that correspond to Alzheimers/dementia. are things to look after, sure. But *how* you choose to learn is likely a huge factor in maintaining your mental acuity with age.
posted by Ryvar at 2:39 PM on December 14, 2007 [4 favorites]


Assuming one lived to be 10 million years old or whatever, wouldn't the brain either

1) Grow to accomodate the increased memory requirements.

or

2) Just forget memories with little use.

I've heard of taxi drivers having different MRI readings, due to the development of a portion of the brain used for remembering maps. But conversely, I can't remember much from when I was 5 years old, likely because I don't really use those memories much (and considering cells die and regenerate renewal should be an issue).
posted by Orange Pamplemousse at 2:39 PM on December 14, 2007


Orange: You've generally got the right idea, but brain cells don't 'die' and rarely grow (neurogenesis) in adults. They decouple due to background electrochemical noise, and learning several semi-related topics and analyzing the interconnections between them *seems* to be the only reliable method of sparking adult human neurogenesis.
posted by Ryvar at 2:51 PM on December 14, 2007


Ahh, my mistake. Brains aren't really my forte, and I thought only certain specialized brain cells (those related to scent in particular) weren't replaced (as opposed to the majority of such cells).
posted by Orange Pamplemousse at 2:58 PM on December 14, 2007


Ryvar: Wasn't there a study recently about exercise stimulating neurogenesis, especially in the memory portions of the brain?
posted by stratospark at 3:18 PM on December 14, 2007


strato: I haven't kept up with developments in the past couple years, but I can certainly believe it. With so much of the brain involved with the operational minutiae of the body, it stands to reason that improving the body forces some pretty heavy refactoring down the pipe.
posted by Ryvar at 3:25 PM on December 14, 2007


IIRC, David Deutsch thinks the brain may involve quantum processes, which could mean that it is capable of orders of magnitude more calculations than would be construed from its molecular makeup.
posted by weapons-grade pandemonium at 6:54 PM on December 14, 2007


These two guys haven't run out of room yet.
posted by weapons-grade pandemonium at 7:02 PM on December 14, 2007


Some people seem to be saying that old memories get "overwritten". It was always my belief that we never lose any memories, we simply forget how to access them. Of course damage, decay, background radiation and the entropy of atoms not withstanding.

So in theory, if you came up with an mnemonic device to remember all the details about something (say, the names of every species in the family Hominidae), and used another "key" mnemonic device to periodically refresh/manage/remember all your other mnemonic devices, you could store long term data perfectly and indefinitely.

But with human brains forgetting the "key" doesn't mean you lose all the data, it just allows it to start to degrade as it isn't properly refreshed periodically.

But if later on you all of a sudden remembered how to access those mnemonic devices - bam you would have access back to those previously "forgotten" memories. Kind of like opening a folder on your computer. You can't remember the memories, until you remember how to remember them. It's always been my belief that humans do this subconsciously, but if you did it consciously you could remember just about anything you would ever want.

There are severe time restrictions though, you would literally be spending hours per day maintaining your memory. This IS possible, as avid users of programs such as Supermemo can attest to, it just takes a lot of concerted effort. So you could basically fill your mind up with as many memories as you could, until your brain spent 100% of it's time on maintaining the memories it already has.

I made up this theory one day after remembering something that I had long since "forgotten" in detail.
posted by parallax7d at 7:10 PM on December 14, 2007


All I know is that after a significant number of years not even thinking of the television program in question, and apropos of nothing one day while I was getting out of my car, my brain decided to remind me that the name of the meeting place in Three's Company was called the Regal Beagle.

Mind you, I tend to be a sponge when it comes to information. So if that little trinket of useless garbage was (and is) bouncing around in my head, I can only imagine that memory is for all purposes limitless if you're patient enough to wait around for your brain to recover the information.
posted by davejay at 9:31 PM on December 14, 2007


parallax7d - your theory reminds me of that bit about how you can store any information in the world on a single ruler. All you have to do is make a mark .5 of the distance across it, and you've stored the number 5. Make a mark .521 of the way across it, and you've stored 521. Assuming you have an accurate enough way to mark it and measure the marking, you can store a number of any length. And since any information can be expressed as a chain of numbers, you could store the works of Shakespeare (in any order you like) on a ruler with one well-placed mark.

So "in theory" if you can remember where you put that mark, you can remember anything. This seems to be stretching even the theoretical limits of the mind to say the least. A series of mnemonics to remember mnemonics to remember everything is similarly interesting yet impractical.

Still, the raw storage capacity in bits seems pretty up there. The brain stores information as connections between nerve cells, each of which can make several with many others. It's a far more sophisticated storage structure than an abacus, so different, probably, that even describing it in bits may not be applicable. But in any case there should be a numeric range of how many cells and connections per cells most brains fall within. I think you'd have to say there's a limit but I doubt we know enough about the brain to name it.

I was thinking the other day about the human genome, too, and how it holds something like 5 billion nucleotide pairs. I don't know if it's a 4 permutation system (AT, TA, GC, CG) or if it's just AT & GC. I don't think that AC is a valid base pair, etc. I am not a geneticist or a computer scientist... but if you do the math on 5 billion bits in gigabytes seems like about a gigabyte of information. Not that much at all... Even if someone corrects me and it's more like 12GB, it's still a crazy small amount of info to code a human... I guess there's the epigenome to think about and such... anyway, I'm rambling off topic.
posted by scarabic at 9:51 PM on December 14, 2007


The brain stores information as connections between nerve cells, each of which can make several with many others.

Is this true? Because memories can be created pretty quickly, and nerves grow pretty slowly, and neurotransmitters are pretty transient. I wish I knew exactly what a memory was, in physiological, biochemical terms. There seems to be a lot of handwaving about this issue (not pointing at scarabic, I am just curious). It seems that without a firm handle on the physical nature of neural storage in humans, then discussing the capacity of the brain is going to be quite fruitless.
posted by Rumple at 11:02 PM on December 14, 2007


I don't think it requires the growth of cells (which I've also heard is slow) to map neural connections. To my understanding, which I admit is weak, a given cell can actually change its connectedness to others. The map can be rewired. If you suffer nerve damage and need to grow new cells, yeah, you're in for a wait. I think extant cells have some ability to respond and change.

I'm sure this is all vastly more complex, to the point where my layperson's understanding is not only incomplete but wrong.
posted by scarabic at 9:15 AM on December 15, 2007


Scarabic, it may help to think of the genome as a book, with each gene a collection of 'words' consisting of 4 different letters (for lack of a better name).

The book can be read either forwards or backwards, and each 'letter' is a base pair. Therefore, for the short word:

ATC
TAG

You can actually read 4 different things. ATC, CTA, TAG or GAT. Since there are no spaces, you could even make a large number of 2 letter words, either by omitting a letter or starting in the middle of our word.

ex. AC, TC, or AT for the top, from left to right.

Broadly, this is how so much genetic information is stored in a simple 4 letter string. Alternative splicing (as the creation of the AC/CA/TG/GT words are known) lets one short stretch of DNA code for several proteins, which may or may not have related function. On top of that you have the epigenetic factors, which control gene expression in any number of ways (protein inhibitors/activators, CpG islands disable 'activating' genetic codes, hell, even the concentration of whatever solutes in the cell when it is formed from the mother cell).


I don't know how the brain actually works (see above for proof), but it sounds like memory is stored in the basic structure of the neural net (ie. not in the cells, but in the pattern of links and nodes). Cells can change their structure relatively easily, allowing bacteria/white blood cells to move autonomously without the use of cilia or flagella. In this way it would be pretty easy for neural cells to change the shape of their net, but says nothing about their ability to divide.

So making a memory is easy but if a net were cut in half, with dead cells in the middle, it would be very difficult for the gap to be bridged. Once connectiveness is restored, all is well (ie. amnesia) but getting to that point is the issue.
posted by Orange Pamplemousse at 11:12 AM on December 15, 2007


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