Author Topic: To what extent do the neurons in the brain follow a 'design'?  (Read 1998 times)

Offline Daniel

  • Administrator
  • Experienced Linguist
  • *****
  • Posts: 1539
  • Country: us
    • English
To what extent do the neurons in the brain follow a 'design'?
« on: December 22, 2013, 01:42:14 AM »
Is the distribution of neurons random? Do they develop connections at random (based on input)?

It's hard to imagine how the actual locations and specific connections of neurons could be encoded in our DNA. It probably varies a LOT by person and also we adapt so easily to change (such as when some neurons die from damage-- the vast majority of the time we don't even notice-- drinking alcohol kills a few neurons each time, but it isn't, in moderation, problematic).

We have about 86 billion neurons, each connected to about 1000 others. If any information about specific location or connections were encoded in our DNA, the information encoded in the DNA would be vast! I came across an article the other day that suggested the number of 'switches' in a single human brain outnumbers the entire number of equivalent 'switches' in all computers on the planet.

So... I conclude, just by simple and superficial logic, that the details of the arrangement of neurons is not genetic. There is no "design". Clearly there are certain distributional aspects to us genetically, such as where large clusters of neurons go (in the head, not the feet), but I doubt it gets into any sort of detailed neuron-by-neuron level at all.

It is possible that the pattern is somehow determined by growth: an initial connection is pre-established genetically and from that the rest automatically follow based on the programming attached to each individual neuron. Or maybe they're just randomly distributed to general areas and then random connections occur until something fits right.

Either way, if what I'm suggesting is remotely accurate, then the implications for modeling the human brain are profound: all that is required is (roughly) the number of neurons in each broad region and the behavior of neurons. The rest follows directly from those two.


Computer models of neural networks are often crudely designed: arrange neurons randomly (or just in arbitrary rows/layers) and then allow them to connect to others at random and until something fits, plus some input to the system or training. This seems superficial and like a silly programming experiment, but in fact it actually might be exactly what the brain does! Wouldn't that be crazy?

In short, the information held in the brain is probably around (86 billion / 2) * 1000 = 43 trillion direct, binary connections [each neuron has 1000 half-connections]. And as for the number of potential connections throughout the brain, I think it would be something like (43trillion^[43trillion-1]) [assuming no repetition (cross through the same connection twice), which might mean infinity]. Some ridiculously huge number. And that may be absolutely all there is to intelligence. One neuron alone is basically a 0 or a 1. And perhaps that's all our minds are: some huge number of ones and zeros.
[Edit: just fixed some math in there. It's probably not very accurate, but I'd hope vaguely representative.]



If that's all true, then what does it mean for Linguistics? How can "UG" possibly exist, and if so how can it be biological? (Perhaps UG is actually a mathematical requirement on communication systems or symbolic representational systems, if anything at all.) And, even though this questions some of that... how does it all work out anyway? Are we just "smart enough" to do language? We just have enough neurons?
« Last Edit: December 22, 2013, 01:56:25 AM by djr33 »
Welcome to Linguist Forum! If you have any questions, please ask.

Offline Corybobory

  • Global Moderator
  • Linguist
  • *****
  • Posts: 138
  • Country: gb
    • English
    • Coryographies: Handmade Creations by Cory
Re: To what extent do the neurons in the brain follow a 'design'?
« Reply #1 on: December 22, 2013, 04:16:49 AM »
Something about the structure of the brain must be genetic, since it develops in the womb in the first place.  The brain isn't made out of one homogenous type of material either, and it is genetics that create these different areas of the brain and map for the proteins and hormones that send messages and allow our body to 'know' how to grow.  Most of our thinking doesn't come from learning input, either - neurons are firing that allow us to breathe, and our organs to function.  This doesn't all come from learning or the development of a completely blank slate brain.  So if all that can organize itself from genetics - I imagine a whole lot else can too. 

But this is all from a product of long slow evolution.  I agree that  'universal grammar' is unlikely to have evolved or even be selected for - but I don't know if the immense amount of neurons supports this.

BA Linguistics, MSt Palaeoanthropology and Palaeolithic Archaeology, current PhD student (Archaeology, 1st year)

Blog: http://www.palaeolinguist.blogspot.com
My handmade book jewellery: http://www.coryographies.etsy.com

Offline lx

  • Global Moderator
  • Linguist
  • *****
  • Posts: 164
Re: To what extent do the neurons in the brain follow a 'design'?
« Reply #2 on: December 22, 2013, 04:54:49 AM »
Well, there must be some design to the whole system, right? I mean we all have specific regions that host different clusters of cells in the brain that display similar functions across the species. The Brodmann Classification System would just make no sense if there wasn't an underlying structure that tied clusters of neurons that carry out a specific function to a specific area. Having said that, we all know that this isn't fixed and damage to one locus of the brain can result in even the other hemisphere taking on the load and rewiring of those specific functions, all demonstrations of Hebbian theory ("Neurons that fire together, wire together.")

There would have to be a basis, but on top of that basis, a loose system of inter-connectivity that had the freedom to join and be moulded based on specific electrical input. The architecture must be there and if your question is about what happens after that architecture is in place, then I understand your question a bit more. When you look at genetic motor disorders, there is a lot of convincing evidence that this caused by the distribution of neurons in an atypical fashion (genetically inherited) which is likely to have been inherited in the genetic code and therefore mapped via some building block (plan) that would imply a pretty specific plan of neuronal distributions. Having said that, there is clearly some crazy acrobatic qualities to the system and the interplay of those systems is not something I believe is well understood in neuroscience in general.
« Last Edit: December 22, 2013, 04:56:24 AM by lx »

Offline freknu

  • Forum Regulars
  • Serious Linguist
  • *
  • Posts: 397
  • Country: fi
    • Ostrobothnian (Norse)
Re: To what extent do the neurons in the brain follow a 'design'?
« Reply #3 on: December 22, 2013, 05:08:53 AM »
I'd like to share a word that I may have coined in a discussion with a close friend of mine — it probably has been used before — "neuroplasticity".

Both physically and mentally our minds are quite "plastic", or mouldable, responding to both internal and external "stimuli" of various kinds. So although we most certainly do have some kind of inherent "design" to our brains, like any other part of our body, it wouldn't surprise me if the brain was able to "reshape" itself to environmental pressure.

By this I mean people who have suffered brain damage, particularly in the language specific regions, yet who seem to have regained their abilities as the brain "moulds" itself, with undamaged regions taking on the functions of the damaged regions.

So although there is an inherent "design" and a seemingly basic foundation for our higher-level functions, it might not necessarily be the only arrangement that works. The result of evolution, but not set in stone.

Or at least when it comes to the neocortex? The deeper you go into the brain, the closer to autonomous functions, this probably doesn't hold anymore. This might even be the evolutionary advantage of our large neocortex.

Or? Neurology isn't exactly my specialty, lol

Offline jkpate

  • Forum Regulars
  • Linguist
  • *
  • Posts: 130
  • Country: us
    • American English
    • jkpate.net
Re: To what extent do the neurons in the brain follow a 'design'?
« Reply #4 on: December 22, 2013, 05:28:31 AM »
Neurobiology is not my speciality either, but I understand that recently neuroscientists have found that neurons tend to be organized in "motifs" (AKA "neural legos"), which are small groups of neurons (10 or fewer neurons) with the same patterns of connections between them. I blogged about this a few months ago, talking about Markram and Perin (2011) and Perin, Berger, and Markram (2011). The general idea is that Hebbian learning relies on having varying connection strengths between neurons, but neurons in these motifs appear to have the strongest connections that are biologically possible (the connections are saturated). Thus, meaningful learning occurs only between the motifs: it cannot happen within a motif. This means that a motif is effectively a deterministic transformation of its inputs, and different motifs may perform different transformations.

I agree that it is unlikely for individual connections to be genetically coded. However, I think it is possible for the relative prevalence of various motifs in different regions to be genetically coded; some regulation sequence makes a particular motif (= deterministic transformation of inputs) more or less likely at some point in development. I'm not sure how this would fit with the particular view of UG that has been developed in the Generativist literature. However, if we are willing to consider a broader view of UG, then UG may just be a particular probability distribution over these motifs, or over structures of these motifs.

All of this is highly speculative, of course. As far as I know, these motifs have not been directly implicated in language behavior, and may be too low-level to have any discernible reflex in language.
« Last Edit: December 22, 2013, 05:39:20 AM by jkpate »
All models are wrong, but some are useful - George E P Box

Offline Daniel

  • Administrator
  • Experienced Linguist
  • *****
  • Posts: 1539
  • Country: us
    • English
Re: To what extent do the neurons in the brain follow a 'design'?
« Reply #5 on: December 22, 2013, 06:24:07 AM »
Some great replies!

Quote from: Cory
Something about the structure of the brain must be genetic, since it develops in the womb in the first place.  The brain isn't made out of one homogenous type of material either, and it is genetics that create these different areas of the brain and map for the proteins and hormones that send messages and allow our body to 'know' how to grow.  Most of our thinking doesn't come from learning input, either - neurons are firing that allow us to breathe, and our organs to function.  This doesn't all come from learning or the development of a completely blank slate brain.  So if all that can organize itself from genetics - I imagine a whole lot else can too. 
I'm not convinced. By "input" I don't necessarily mean human consciousness level input. Input might be something as simple as chemical processes resulting in lower oxygen in one part of the brain if something does or doesn't occur. What I mean to focus on is the neurons themselves: what creates the distribution and associations?
Certainly some of this is genetic, but where is that line? In an indirect sense, it is perhaps all genetic. Then another way of looking at it is this: is the human brain special in its organization or just its parts?

Quote
But this is all from a product of long slow evolution.  I agree that  'universal grammar' is unlikely to have evolved or even be selected for - but I don't know if the immense amount of neurons supports this.
Agreed. Humans are certainly genetically capable of language, but to hint that there's some linguistic structure encoded in the DNA is, I think, an extreme position. Moreover, what I find really hard to understand is how it would be implemented neurologically if neurons are not distributed and attached based on DNA.

As I understand Chomsky's argument (or perhaps more from the Biolinguists who closely associate with his most recent ideas), the idea is that human language evolved about 100,000 years ago suddenly with one simple change-- therefore, Minimalism is the project trying to find that simple change. It was described to be as "a specific neural circuit" [that is unique to language and the biological encoding of Merge].

Among many objections I have.... how could such a circuit be implemented in the DNA?

Or do those bioliguists just have no idea what they're talking about in terms of brain circuitry, using awkward, inaccurate metaphors about "circuits" then they really mean algorithm?

Quote from: lx
Well, there must be some design to the whole system, right?
Why. I don't take that as a given. It's an expected first assumption, and it may also be correct. But let's not start by assuming it is axiomatically true.
Quote
I mean we all have specific regions that host different clusters of cells in the brain that display similar functions across the species. The Brodmann Classification System would just make no sense if there wasn't an underlying structure that tied clusters of neurons that carry out a specific function to a specific area. Having said that, we all know that this isn't fixed and damage to one locus of the brain can result in even the other hemisphere taking on the load and rewiring of those specific functions, all demonstrations of Hebbian theory ("Neurons that fire together, wire together.")
Locations in the brain are notoriously difficult to find (eg, the whole "modularity of language" thing, or even just finding out where language neurons are beyond some of the basics). And they can change.

I would certainly agree with you: the general layout of the brain is definitely genetic, just as much as having feet and no tail is. But that's roughly a mold then. Within that mold, are the neurons themselves structured genetically? Or are they more like some kind of concrete, poured into a mold and left to fill and solidify in naturally?

For example, I can imagine a specific gene that determines the size of some specific region in the brain and something about the kinds of cells that go in it. But that is still remarkably little! Or is the actual location somehow relevant to why humans are so good at thinking? What if the brain were somehow inverted in a crazy way? Would that not work? Is there anything unique and important about the human brain, or is it just that roughly anything along those lines would work out for us?


More importantly, there is another explanation for localization: input. The brain operates in layers and the outermost neurons are, of course, in contact with various kinds of input, such as in the ears. It would be very odd if some ear-related part of the brain was located near the spinal chord; we expect it to be near the ears. And so it might just be a usage/input effect where whatever layers happen to connect eventually reach the right configuration.

Quote
There would have to be a basis, but on top of that basis, a loose system of inter-connectivity that had the freedom to join and be moulded based on specific electrical input. The architecture must be there and if your question is about what happens after that architecture is in place, then I understand your question a bit more.
Agreed, and yes.
To abstract away a bit more (and perhaps clarify what I'm thinking about), imagine trying to build a mind on a computer-- would it require a specific kind of neural network with exactly a certain configuration? Or could it approximate the distribution, properties and density of neurons in the brain and just randomly cycle until it worked?

Quote
When you look at genetic motor disorders, there is a lot of convincing evidence that this caused by the distribution of neurons in an atypical fashion (genetically inherited) which is likely to have been inherited in the genetic code and therefore mapped via some building block (plan) that would imply a pretty specific plan of neuronal distributions.
This is very relevant. But is it certain that the genetic inheritance is not in the form of broken neuron instructions? That is, the actual structure of the brain is not genetic, but there is some genetic mutation that causes a specific type of neuron (perhaps in combination with some other factor) to not generate a normal brain?

Quote
Having said that, there is clearly some crazy acrobatic qualities to the system and the interplay of those systems is not something I believe is well understood in neuroscience in general.
Quite literally, individual neurons appear to respond to specific stimuli, such as a certain color of light at a particular angle in a particular corner of the eye. There's a neuron for that. But obviously if that particular neuron dies, along will fill in, etc. (Probably with some redundancy too.)
That's a very powerful ability and completely structurally based. But with the flexibility, it looks less and less like any particular neuron (and therefore any group of neurons) has any predetermined properties, except roughly where they end up in the body. With 86 billion neurons, let's even say there are 86 specific subareas with unique dimensions. That's fine. But there are still one billion neurons in each area not distributed or connected by specific instructions in the DNA!


Freknu, neuroplasticity is used quite a bit (I've come across it especially for discussions of language acquisition, but that's a tangent).
Quote
Both physically and mentally our minds are quite "plastic", or mouldable, responding to both internal and external "stimuli" of various kinds. So although we most certainly do have some kind of inherent "design" to our brains, like any other part of our body, it wouldn't surprise me if the brain was able to "reshape" itself to environmental pressure.
If reshape, then why not shape as well?

Quote
Or at least when it comes to the neocortex? The deeper you go into the brain, the closer to autonomous functions, this probably doesn't hold anymore. This might even be the evolutionary advantage of our large neocortex.
This is, I think, a crucial point. Let's phrase it as a question: does the distribution (and/or attachment) of neurons correlate more closely with genetics for the more core functions? Are the neurons that control the heart and lungs any more/less plastic or randomly distributed than those for language or those for creating art?
You may very well be right, but if so, why?

Quote
Or? Neurology isn't exactly my specialty, lol
Me neither. I'm coming from Linguistics > Psychology > Neuroscientist (plus maybe a stop by computational theory on the way). I wouldn't even consider myself a psychologist, must less neuroscientist. But it is interesting!

Quote
I understand that recently neuroscientists have found that neurons tend to be organized in "motifs" (AKA "neural legos"), which are small groups of neurons (10 or fewer neurons) with the same patterns of connections between them.
This is what I'm talking about. Looks like it's cutting edge research, so maybe this is a good question for the moment after all :)

See my note about Chomsky, Minimalism and Merge above: I imagine they'd want the "Merge/language circuit" to be a type of motif!


Now I have a few things to read. Thanks for the links.

Quote
I agree that it is unlikely for individual connections to be genetically coded. However, I think it is possible for the relative prevalence of various motifs in different regions to be genetically coded; some regulation sequence makes a particular motif (= deterministic transformation of inputs) more or less likely at some point in development.
What you're describing seems more like an unstructured version: neurons are predetermined to do certain things but they get distributed randomly. And in some cases (perhaps even most/all) the neurons may be set up / released in prefabricated configurations, but then still sent out randomly. In other words, for a computer program modeling this you'd just need an example of that "motif" and then at that point just send a bunch of those out into that region of the brain and work from there.

Quote
I'm not sure how this would fit with the particular view of UG that has been developed in the Generativist literature. However, if we are willing to consider a broader view of UG, then UG may just be a particular probability distribution over these motifs, or over structures of these motifs.
Yes, much more reasonable. Still far from proof that "UG" is anything special, though. (It might just be more of the same, from elsewhere.)

Quote
All of this is highly speculative, of course. As far as I know, these motifs have not been directly implicated in language behavior, and may be too low-level to have any discernible reflex in language.
I wonder if the biolinguists would attach themselves to such a claim. I wouldn't be surprised. I don't really know though.
Welcome to Linguist Forum! If you have any questions, please ask.

Offline lx

  • Global Moderator
  • Linguist
  • *****
  • Posts: 164
Re: To what extent do the neurons in the brain follow a 'design'?
« Reply #6 on: December 22, 2013, 08:11:10 AM »
Quote
Locations in the brain are notoriously difficult to find (eg, the whole "modularity of language" thing, or even just finding out where language neurons are beyond some of the basics). And they can change.
Is this not a bit of a cherry-picked example, though?
You can hardly call one of the great mysterious - of where language is stored in the brain - a typical example of the ordinary difficulty of finding functional localisation in the brain, right? I mean, to counter that example with the ease of finding the sensory systems relating to vision, pain, fear etc., that is pretty banal research because ordinary MRI scans can just tell you what part of the brain is activated. Now for complex systems, like language, that use elements from all across the spectrum and have fantastically articulate nuances that are postulated to occur, that becomes a horrible task because you can't easily separate out the inputs and direct brain responses without taking into account a whole host of other activity that is clouding the picture. In general, when you can have direct stimulus-response experiments, I wouldn't have thought that it was a typically 'difficult' job to find where the localised functionality seemed to be taking place.
Quote
Quite literally, individual neurons appear to respond to specific stimuli, such as a certain color of light at a particular angle in a particular corner of the eye. There's a neuron for that. But obviously if that particular neuron dies, along will fill in, etc. (Probably with some redundancy too.)
Yes, this idea of neural stem cells that are called in to replace other cells that have become inactive (through cell death or whatever else) is important to keep in mind, but doesn't that presuppose the existence of a pre-determined neuronal plan?

Offline Daniel

  • Administrator
  • Experienced Linguist
  • *****
  • Posts: 1539
  • Country: us
    • English
Re: To what extent do the neurons in the brain follow a 'design'?
« Reply #7 on: December 23, 2013, 12:57:54 AM »
Quote
Is this not a bit of a cherry-picked example, though?
You can hardly call one of the great mysterious - of where language is stored in the brain - a typical example of the ordinary difficulty of finding functional localisation in the brain, right?
You might be right! I'm a linguist, not a neuroscientist so I know very little about the brain beyond linguistics.
Do we, on average, know where most things are located? If so, then it is a bad example. I don't know. I wasn't trying to pick one I thought was unrepresentative, though. I would agree that some functions of the brain are less mysterious-- a lot is known about vision, for example.
But at the same time:
1. I would imagine that most/many of the systems that have certain locations are due to being in contact with specific input/output connections. And that isn't interesting at all-- even in a completely random distribution we'd expect the things nearest input/output connections to relate in function to those connections.
2. We may be able to generally say "that part is for vision", but do we know exactly what happens within each of the parts? In other words: is the amount of location specificity impressive or just like a general blueprint for the brain? That could easily be encoded in DNA. What I'd be more interested in would be whether anything more specific is encoded.

Quote
I mean, to counter that example with the ease of finding the sensory systems relating to vision, pain, fear etc., that is pretty banal research because ordinary MRI scans can just tell you what part of the brain is activated. Now for complex systems, like language, that use elements from all across the spectrum and have fantastically articulate nuances that are postulated to occur, that becomes a horrible task because you can't easily separate out the inputs and direct brain responses without taking into account a whole host of other activity that is clouding the picture. In general, when you can have direct stimulus-response experiments, I wouldn't have thought that it was a typically 'difficult' job to find where the localised functionality seemed to be taking place.
Right, I agree more or less. But again how narrow is this, and important how consistent is it? I'm not surprised that an MRI can tell you which areas are active for anything (this works for language too), but to identify a consistent human brain location (encoded in the DNA) takes a bit more. Is it by random chance and trial and error that it ends up there for each of us (due to how neurons work) or is it predetermined in the DNA?

Quote
Yes, this idea of neural stem cells that are called in to replace other cells that have become inactive (through cell death or whatever else) is important to keep in mind, but doesn't that presuppose the existence of a pre-determined neuronal plan?
It might! Certainly that's one explanation. There are others, at least two, that I can think of:
1. These responses aren't unique. At least sometimes, that's true:
Heit, G., Smith, M. E.,  Halgren, E. (1988). Neural encoding of individual words and faces by the human hippocampus and amygdala. Nature 333: 773-775. doi:10.1038/333773a0 (A fascinating paper anyway... individual words, individual neurons!)
So I don't know that "replacement" is accurate, rather than "redundancy".
2. When a neuron is lost, another might fill the gap due to some kind of general repair procedure-- fill missing link. Or perhaps this is due to simply rewiring around that neuron such that, on average, the loss of one neuron doesn't substantially change all of the paths. When working with huge numbers of paths, maybe each neuron is not really all that important.



So I'm not claiming nothing is genetic or that everything is, but I'm wondering where the line can be drawn. There are two theories I can imagine:

The pre-determined, genetic theory: every neuron and every connection is determined by genetics.

The gas particles theory: just like gas (or liquid) molecules, neurons bounce around and attach randomly within the confines of the space in the brain. [Ok, maybe not "bounce around", but develop, grow and connect randomly, without pre-determined goals.]

Both theories are certainly wrong; it's a mix of both. But how much?
Welcome to Linguist Forum! If you have any questions, please ask.