# Capacity of the brain **URL:** \ **Category:** Factual Questions\ **Created:** [November 26, 2016, 9:23pm UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086 "2016-11-26T21:23:32Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![aldiboronti](https://avatars.discourse-cdn.com/v4/letter/a/9fc348/32.png) [@aldiboronti](https://boards.straightdope.com/u/aldiboronti)\ **Post date:** [November 26, 2016, 9:23pm UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/1 "2016-11-26T21:23:32Z")
Homer Simpson said once that his brain was full and he had to forget old stuff in order to learn new. Clearly the human brain does have a limited capacity. There must come a point when there is just no more room to store fresh information. Do we have any idea what that capacity is? Has anyone, apart from Homer, ever come close to that capacity? If they did approach it could they indeed try to forget things so as to add new? Is it even possible to deliberately forget something? If I could remember every single thing I did in one day, to run it back like a continuous film, how many days could I store? A week, a month, a year, a lifetime? And let me apologize for my own poor brain which behind the door marked Cognitive Science has rows upon rows of empty shelves with just a few books by Daniel Dennett and Steven Pinker lying at the end of one of them. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 26, 2016, 9:43pm UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/2 "2016-11-26T21:43:15Z")
I suspect that as the limit, whatever it is, is approached, it manifests not in a decrease in number of memories, but in their fidelity. ---
**Author:** ![Ignotus](https://avatars.discourse-cdn.com/v4/letter/i/ecc23a/32.png) [@Ignotus](https://boards.straightdope.com/u/Ignotus)\ **Post date:** [November 26, 2016, 9:52pm UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/3 "2016-11-26T21:52:01Z")
I’ve never had to make a conscious effort to forget stuff I haven’t used in years. It seems to happen automatically. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [November 26, 2016, 9:56pm UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/4 "2016-11-26T21:56:43Z")
I feel like I have to forget old things to learn new ones but it’s clearly more complex than that. ---
**Author:** ![photo-guy](https://avatars.discourse-cdn.com/v4/letter/p/858c86/32.png) [@photo-guy](https://boards.straightdope.com/u/photo-guy)\ **Post date:** [November 26, 2016, 10:07pm UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/5 "2016-11-26T22:07:55Z")
The brain is comprised of millions of synapse’s which tie together in unlimited ways to bring back millions upon millions of memories… And probably more… 🙂 They build themselves from a lead given by some slight instigation… A name, smell, etc… There are those called savants who can remember _everything_ they’ve ever read… Thousands of books…, and the page numbers it’s on too… And they can speed read when they do that reading too… It’s fairly easy to remember an entire day by seeing a single photograph of something you did that day… There is virtually no limit to what a brain can do…, or store… Except when it’s deprived of the chemicals, amino acids, or whatever healthy brains need to work well. ---
**Author:** ![aldiboronti](https://avatars.discourse-cdn.com/v4/letter/a/9fc348/32.png) [@aldiboronti](https://boards.straightdope.com/u/aldiboronti)\ **Post date:** [November 26, 2016, 11:33pm UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/6 "2016-11-26T23:33:06Z")
> [@photo-guy](#): > > The brain is comprised of millions of synapse’s which tie together in unlimited ways to bring back millions upon millions of memories… That’s interesting. I hadn’t thought of the combinatorial power of synapses. Does this indeed then make the brain practically unlimited? For instance, were it possible to get it in there, could all the information on the internet fit inside our brain and still leave room for more? ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [November 27, 2016, 12:05am UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/7 "2016-11-27T00:05:44Z")
> [@aldiboronti](#): > > That’s interesting. I hadn’t thought of the combinatorial power of synapses. Does this indeed then make the brain practically unlimited? For instance, were it possible to get it in there, could all the information on the internet fit inside our brain and still leave room for more? A related question is how genes “build” brains. The genome is really small relative to the complexity of the brain, so again it’s the power combinatorics, and most likely the genetic changes that tweak the brain incrementally are subtle regulatory changes in level or location of expression of genes. The brain builds up a lot of its synaptic connections by interacting with the environment, but of course the general _principles_ it follows in doing this are genetically determined. And many quite specific behavioral traits have high heritability. It’s a really interesting question just how a genetic mutation directly or indirectly effects a “rewiring” of the brain to produce a specific behavioral phenotype. We know little about this. ---
**Author:** ![septimus](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/septimus/32/410_2.png) [@septimus](https://boards.straightdope.com/u/septimus)\ **Post date:** [November 27, 2016, 2:04am UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/8 "2016-11-27T02:04:39Z")
The human brain has been estimated to have 150 trillion synapses; each synapse is not a “bit” but is continuously variable. Memories are _distributed_ — instead of making major changes at a few synapses, an event might effect a very tiny change in each of many hundreds of millions of synapses. Computer algorithms may give some insights. Among various types of “neural network,” an [associative memory](https://en.wikipedia.org/wiki/Sparse_distributed_memory) has been proposed to emulate brain. [Another well-known distributed memory algorithm](https://en.wikipedia.org/wiki/Bloom_filter) demonstrates that _some_ associative memory tasks have a small fixed cost independent of the complexity of the memorized stimulus. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [November 27, 2016, 2:36am UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/9 "2016-11-27T02:36:07Z")
> [@Chronos](#): > > I suspect that as the limit, whatever it is, is approached, it manifests not in a decrease in number of memories, but in their fidelity. Current research suggests that every time a memory is recalled, it is altered. ---
**Author:** ![Wesley\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wesley_clark/32/20581_2.png) [@Wesley\_Clark](https://boards.straightdope.com/u/Wesley_Clark)\ **Post date:** [November 27, 2016, 3:33am UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/10 "2016-11-27T03:33:42Z")
I found this link, but seeing how the author says the brain has 1 billion neurons (it is actually 100 billion, plus glial cells play a role in memory too and there are 50-100x more of those than neurons) I don’t know how trustworthy it is. > **[What Is the Memory Capacity of the Human Brain?](https://www.scientificamerican.com/article/what-is-the-memory-capacity/)** > > Paul Reber, professor of psychology at Northwestern University, replies > [@](#): > > The human brain consists of about one billion neurons. Each neuron forms about 1,000 connections to other neurons, amounting to more than a trillion connections. If each neuron could only help store a single memory, running out of space would be a problem. You might have only a few gigabytes of storage space, similar to the space in an iPod or a USB flash drive. Yet neurons combine so that each one helps with many memories at a time, exponentially increasing the brain’s memory storage capacity to something closer to around **2.5 petabytes** (or a million gigabytes). For comparison, if your brain worked like a digital video recorder in a television, 2.5 petabytes would be enough to hold three million hours of TV shows. You would have to leave the TV running continuously for more than 300 years to use up all that storage. > > The brain’s exact storage capacity for memories is difficult to calculate. First, we do not know how to measure the size of a memory. Second, certain memories involve more details and thus take up more space; other memories are forgotten and thus free up space. Additionally, some information is just not worth remembering in the first place. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 27, 2016, 4:19am UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/11 "2016-11-27T04:19:24Z")
Well, there must be _some_ finite limit to the memory capacity of the brain, given that it’s made up of matter, and a finite number of particles. And of course any estimate based on just the number of particles is going to be a huge overestimate, given that the brain doesn’t store information perfectly optimally. In practice, though, I suspect that the maximum practical capacity is just one lifespan’s worth of memories, on the ground that there can’t have been any pressure to evolve a system with any more capacity than that. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [November 27, 2016, 4:58am UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/12 "2016-11-27T04:58:03Z")
> [@Chronos](#): > > …In practice, though, I suspect that the maximum practical capacity is just one lifespan’s worth of memories, on the ground that there can’t have been any pressure to evolve a system with any more capacity than that. Yes, that would certainly be a good null hypothesis. The brain burns about 20% of the food & oxygen that we use, so we’d expect strong selection to make a brain only as big it needs to be. Animals in general tend to be only as smart as they need to be, and in many evolutionary niches it’s cheaper to just make “firmware” with relatively inflexible behavior patterns. We lucked out that our in our niche being super-smart with flexible intelligence was an advantage, giving us brains that can do a whole lot of interesting stuff. ---
**Author:** ![photo-guy](https://avatars.discourse-cdn.com/v4/letter/p/858c86/32.png) [@photo-guy](https://boards.straightdope.com/u/photo-guy)\ **Post date:** [November 27, 2016, 6:19am UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/13 "2016-11-27T06:19:59Z")
> [@aldiboronti](#): > > That’s interesting. I hadn’t thought of the combinatorial power of synapses. Does this indeed then make the brain practically unlimited? For instance, were it possible to get it in there, could all the information on the internet fit inside our brain and still leave room for more? I wouldn’t really know how high that limit is… But the hypnotism’s that brings back what are thought to be other lives is now thought to be those of our parents and grandparents memories…, and so on back for many generations I’m sure… Our long strings of so called junk DNA has all this information stored but we don’t know how to access it otherwise… It has all their memories too… The why of with hypnotism that people can all of a sudden play the piano, talk a foreign language, or know other things they do not know in their current life… It all makes sense… There’s no such thing as ‘instinct’… It’s all remembered things from our parents and on back to distant ancestors… It’s all stored in our genes… Our DNA… And the synapse work to search it out what it’s clued into looking for… As far as I’ve been able to learn and understand… ---
**Author:** ![simster](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/simster/32/1047_2.png) [@simster](https://boards.straightdope.com/u/simster)\ **Post date:** [November 27, 2016, 6:28am UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/14 "2016-11-27T06:28:03Z")
> [@Qadgop\_the\_Mercotan](#): > > Current research suggests that every time a memory is recalled, it is altered. That explains why the fish keep getting bigger. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [November 27, 2016, 6:38am UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/15 "2016-11-27T06:38:44Z")
> [@photo-guy](#): > > I wouldn’t really know how high that limit is… But the hypnotism’s that brings back what are thought to be other lives is now thought to be those of our parents and grandparents memories…, and so on back for many generations I’m sure… Our long strings of so called junk DNA has all this information stored but we don’t know how to access it otherwise… It has all their memories too… The why of with hypnotism that people can all of a sudden play the piano, talk a foreign language, or know other things they do not know in their current life… > > It all makes sense… There’s no such thing as ‘instinct’… It’s all remembered things from our parents and on back to distant ancestors… It’s all stored in our genes… Our DNA… And the synapse work to search it out what it’s clued into looking for… > > As far as I’ve been able to learn and understand… Er, fascinating stuff. When I snap my fingers, you will wake up and forget everything Deepak Chopra has told you. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [November 27, 2016, 7:42am UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/16 "2016-11-27T07:42:15Z")
> [@photo-guy](#): > > I wouldn’t really know how high that limit is… But the hypnotism’s that brings back what are thought to be other lives is now thought to be those of our parents and grandparents memories…, and so on back for many generations I’m sure… Our long strings of so called junk DNA has all this information stored but we don’t know how to access it otherwise… It has all their memories too… The why of with hypnotism that people can all of a sudden play the piano, talk a foreign language, or know other things they do not know in their current life… > > It all makes sense… There’s no such thing as ‘instinct’… It’s all remembered things from our parents and on back to distant ancestors… It’s all stored in our genes… Our DNA… And the synapse work to search it out what it’s clued into looking for… Sorry, but every bit of that is complete nonsense, except the very first sentence. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [November 27, 2016, 7:44am UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/17 "2016-11-27T07:44:54Z")
> [@Qadgop\_the\_Mercotan](#): > > Current research suggests that every time a memory is recalled, it is altered. I read that somewhere, but I remember it differently. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [November 27, 2016, 3:47pm UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/18 "2016-11-27T15:47:15Z")
> [@John\_Mace](#): > > I read that somewhere, but I remember it differently. Oh, a wise guy, eh? Woob. Now go order your socks. 😃 ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [November 27, 2016, 4:17pm UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/19 "2016-11-27T16:17:09Z")
> [@simster](#): > > > [@Qadgop\_the\_Mercotan](#): > > > > Current research suggests that every time a memory is recalled, it is altered. > > That explains why the fish keep getting bigger. The older I get, the better I was. Works for me. 😃 ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 27, 2016, 6:25pm UTC](https://boards.straightdope.com/t/capacity-of-the-brain/773086/20 "2016-11-27T18:25:35Z")
Or my grandfather, whose weight at birth steadily increased over his life. By the time he died, he was up to 24 pounds at birth. [Next page](https://boards.straightdope.com/t/capacity-of-the-brain/773086.md?page=2)