
Why Does the Neocortex Have Layers and Columns, Learning the World's 3D Structure - jcua
http://www.biorxiv.org/content/early/2017/07/12/162263
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KingMob
Former neuroscientist here.

I have no idea why this paper is at the top of HN, other than that the former
founder of Palm is the lead author.

Setting aside that it hasn't been published or accepted, the only remotely
novel thing seems to be they suggest that location information is represented
in each column, and this occurs everywhere in the neocortex.

Well, what does the actual biology do? On the one hand, it's well-known that
the trillions of long-range connections mean you can find neurons almost
everywhere that will fire in response to place/location stimuli.

On the other hand, the entire medical history of restricted lesions and
targeted deficits (Broca's area, Wernicke's area, patient HM's hippocampal
anterograde amnesia, visual scotomas, etc etc etc) indicate some brain areas
really are specialized for some things more than others.

The brain has some redundancy, but it's such an expensive organ (2% of body
weight, but 20% of your energy budget) that I would not bet on such widespread
replication if avoidable.

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monocasa
> On the other hand, the entire medical history of restricted lesions and
> targeted deficits (Broca's area, Wernicke's area, patient HM's hippocampal
> anterograde amnesia, visual scotomas, etc etc etc) indicate some brain areas
> really are specialized for some things more than others.

Wouldn't the evolutionary history of the brain imply that information is
encoded in two different ways in a lot of cases. Ie. that the components of
the older 'lizard brain' (if you'll excuse the issues with that term) have a
rather fixed function, but the neocortex evolved overrides to those functions?

Like sure, we've got a much better understanding of grid cells and place cells
in the hippocampus, but does that mean that there isn't similar information
being stored in a different way in the neocortex?

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KingMob
In some ways that's true, though the more recent areas tend to
cooperate/elaborate, not replace.

E.g., both the superior colliculus in the midbrain and the frontal eye fields
in neocortex are responsible for making eye movements, but the FEF doesn't
override the SC. Even in this case, it's not like eye gaze/movement info is
dispersed throughout all the cortex, it's limited to a short list.

We also know that the receptive fields (which part of a scene a neuron fires
in response to) increase in size as you go up the visual hierarchy. V1 neurons
will response to tiny parts of a scene, whereas V4/MT and V5 will response to
huge swathes of your vision, indicating they become _less_ location-sensitive.
Object-identifying neurons may well respond to the object _anywhere_ in your
vision, suggesting they're not location-sensitive at all.

I guess Hawkins might argue that it's different neurons in association cortex
columns that encode location, but frankly, the argument from biology is poor.
There _are_ cortical areas mapped out like this... but I can't imagine why
Hawkins thinks this is a governing principle for the _whole_ cerebrum.

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mercer
Thanks for the elaboration! May I ask why you're a _former_ neuroscientist?

~~~
KingMob
Biology is messy. My data weren't so hot. I didn't want to live in small
college towns at the time. Had more fun writing Clojure side projects.

Many, many reasons.

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neuronexmachina
For some context, this paper is from Numenta, Jeff Hawkins' company. Hawkins
was the founder of Palm/Handspring back in the 90s. Afterwards he became quite
interested in neuroscience and neural networks, and pulled a Wolfram in his
2004 book "On Intelligence" with claims that he had a unified theory of how
the brain works.

[https://en.wikipedia.org/wiki/Jeff_Hawkins](https://en.wikipedia.org/wiki/Jeff_Hawkins)

~~~
KingMob
As a former neuroscientist, the majority of people who claim to have grand
unified theories of the brain are those who haven't studied it enough to know
how far we still have to go.

~~~
deepsun
Nevertheless I appreciate his efforts and just bought his book, because having
an idea is way different from putting own money in it. He puts his own money
to neuroscience, and does not compete with real scientists for government
grants.

Other millionaires may buy yachts, or just spread "novel" ideas (e.g.
Hyperloop idea by St. Elon) without investing their own money.

~~~
paladin314159
I appreciate and agree with your perspective on putting your money where your
mouth is, but Elon is the last person to criticize in that context. He quite
literally put all of his money into the problems that he thinks are the most
valuable to work on (whether you agree with him or not).

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deepsun
False. He didn't put a single dollar into Hyperloop (idea that was researched
since 100 years ago, and general conclusion is that it's not worth it, too
expensive to maintain).

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bmcooley
Question from someone who is not knowledgeable in ML or AI: Do current
implementations of ANNs allow trying out these different types of
organizations/structures? Is the structure and workings of neurons
sufficiently similar to ANNs that the architecture transfers, or are there
huge differences that make understanding and development orthogonal?

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aerlinger
The short answer is no, the architectures don't transfer. At least not today.
Biological neurons are much more complex, and therefore behave quite
differently from neurons in neural networks.

To put things in perspective, we've fully mapped the connectome (map of neuron
connections) of the simplest animal, C. Elegans, which has only about 300
neurons, yet we still can't simulate this organism's behavior computationally.

~~~
evincarofautumn
Last I knew, OpenWorm was making good progress on the nervous system
simulations, though. IIRC they’ve demonstrated swimming, retracting when
bumping into walls, and food-seeking.

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hyperion2010
So the implication in the title is almost certainly false. There are columns
and layers in areas of cortex that are responsible for processing sensory
modalities that are not inherently 3d in nature. If I had to guess (from my
vague recollection of the literature) the current thinking is that laminar
structures are a nice way to build things developmentally, and columns arise
in part from development but also because of *otopic mapping, which is to say
that many sensory modalities have a reasonable mapping into two dimensions
that have correlations in their inputs based on the destance their sensors are
from each other. Obviously not the whole story, but laminar and columnar
structures are very likely not 'just' about building 3d representations.

All that said, I could buy an argument that cortex has settled on a 3d
representation because, even though the exact encoding of muscle movements is
most certainly not in x,y,z or other 3 vector representations, a large portion
of the motor actions that we make are indeed in 3d space (a good counter
example being language which has representations in cortex and acts on a very
high dimensional space of our vocal and facial muscles).

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sqeaky
I interpreted the headline as though they meant that the neurons were in a 3d
structure and part of the world.

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mjpuser
He isn't claiming that this is how the brain works, he is just proposing a
model. He describes in some of his talks that his work isn't about replicating
the brain, it's about distilling algorithms from brain function/anatomy.

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etiam
There is a short supplementary video, by the way:

[https://www.youtube.com/watch?v=fhnMUc36opI](https://www.youtube.com/watch?v=fhnMUc36opI)

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partycoder
This paper makes use of hierarchical temporal memory.

I recommend reading this discussion:
[https://cs.stackexchange.com/questions/13089/some-
criticisms...](https://cs.stackexchange.com/questions/13089/some-criticisms-
of-hierarchical-temporal-memory)

