Comment by georgewfraser | Hacker News Reader

Comment by georgewfraser | Hacker News Reader

The premise of this research, that the cortex is broken up into discontinuous “columns”, is only partly true. If you record several neurons that are lined up one on top of another in different layers of the cortex, they will usually respond to the same stimulus or activity: for example, responding to touch on the same finger.

But the word “column” implies discontinuous modules. You can actually observe this in sensory cortex of mice and rats, where each whisker has a 1-1 relationship with a “column” of neurons that primarily respond to that whisker. This observation is what originally led neuroscientists to propose the concept of the column as a fundamental unit of organization of the cortex.

But it turned out that lots of other brain regions don’t have this kind of discontinuous organization. Neuroscientists still use the term “cortical column” but they’re really just referring to the fact that vertically aligned neurons seem to be closely connected.

When the Numenta people talk about “cortical columns” they seem to be describing the original idea of cortical columns that didn’t pan out. It’s really weird.

Not to mention that the blanket assertion that 'columnar' structure is similar across cortex is simply not accurate. Humans seem to have ~180 distinct cortical regions [0], and when we start digging into the actual cytoarchitecture they all start to look different. Yes it is possible to try to shove them all into the '6 layer' model, but if we weren't imposing an extremely strong prior for 6 onto these cell populations we would think that they were all radically different, not uniformly the same as many computationalists and theorists would like to believe.

0. Glasser and Van Essen https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4990127/

knowing practically nothing of this, and more specifically the cytoarchitectural makeup of various cortical regions, I am curious with the following questions: (I dont have a mature lexicon for formulating my questions on this subject - so please take an ELI5 perspective on my questions)

1. Does the stimuli for which a region is responsive to dictate the cytoarchitecture found in that region? Or conversely, does the cytoarchitecture dictate the response-nature of that region?

2. Can we find commonality in cytoarchitecture for regions which respond to a certain stimuli across species? (Is 'touch' always handled by the same cytoarchitecture of brains regardless of mice/men/mammal/reptile/etc?

3. re: 2. - Is 'touch' always handled by the same cytoarchitecture in all Humans? What, if any, differences in cytoarchitecture may be found in language handling regions for people who speak Japanese vs French? Or deaf vs hearing?

4. Is the mass of a a particular region along with its cytoarchitecture corollary to ones given intelligence

Lots of questions....

1. A fascinating question to which we do not have a good answer. We fundamentally do not understand the connection between which cells compose a circuit and how that circuit is related to the spatial and temporal characteristics of the information that it processes. To make an analogy to electronics, we can look at the retina and say "oh, this must do something spatial" and we can look at the tympanic membrane and say "ah! this must do something with frequency" but if you were to compare the purely cellular structures of visual and auditory cortex, you might notice that there were a bunch of spiny stellate cells in layer 4 of one region that were not there in the other, but what that means? We haven't the faintest idea. Note also, that there have been many reports of people with sensory deficits (i.e. blindness, or deafness) having "gain of function" in other cortical regions. It is not clear that this is actually what is going on.

2. Yes. This we do have very strong evidence for. Visual, auditory, somatosensory, olfactory, etc. cortex are present in all mammals and the connectivity patterns between them an other brain structures are conserved. Birds do not have laminar cortex but instead have nuclear (or nucleated) cortex where functional units seem to be organized into nuclei or bundles of cells rather than layers. However, the genes, connectivity, and function of these units seems to be strikingly similar to that of laminar mammalian cortex [0].

3. Cortex is problematic. All vertebrates have basically the same peripheral circuitry for measuring the world. Rods, cones, merkel disks (touch), tastebuds, and olfactory sensory neurons are all highly conserved. So in that sense the answer is yes. We we get to cortex, things change. There is no evidence that there are fundamental cytoarchitectural differences between language. There might be between hearing and deaf, especially if the individual has been deaf from birth. See Carla Shatz work on cortical development [1].

4. No evidence for this. We don't have a very good understanding of how or even whether certain gross anatomical features are related to intelligence. The Human Connectome Project is probably the closest to having population data that could answer the question. Otherwise the geneticists are way ahead [2], but we don't know how their results are manifest in the brain.

0. http://rstb.royalsocietypublishing.org/content/370/1684/2015... 1. https://www.ncbi.nlm.nih.gov/pubmed/8895456 2. https://www.nature.com/articles/mp2014105

Thank you for this response.

The other question/statement i have is;

Is there a discrete number of various cytoarchtectural patterns that can/do exist and are they catalogued? Assuming that through various amino acids and proteins we can get a stem cell to present as various tissue types, can we get them the present as a neuron? But then they cytoarchtecture is probably dictated by genetic coding and not amino-acids/proteins, so steering cell clusters to create a particular 'brain-circuit' is decades away, i assume? Unless there is a way to scaffold the desired outcome by putting new stems cells/neurons next to others which are arranged in the desired format already?

1. To slightly change your question, with regard to the structure of microcircuitry in the brain, of which cytoarchitecture is a purely anatomical component, we are just starting (as in about a decade or two in, but nothing systematic). Cajal and Brodmann did the pure cytoarchitectural studies over 100 years ago, and that is well understood. There are many ongoing projects to gather and characterize this across all human brain regions, most of the effort in the community centers around the BigBrain project, but not all of it is publicly available yet since many of the projects to make use of that data are just finishing their first 'grad student' cycle. On a more fundamental level we are just starting to do a systematic survey of the types of neurons in the brain (previous smaller studies have been done for decades, but have been very hard to compare [1]). We need to have that as a foundation to be able to meaningfully catalogue the circuits that are composed of them. In a bad analogy, we need to have names for the basic discrete circuit components in the brain (resistor, capacitor, transistor, etc.) before we can come up with something like a Horowitz and Hill for the neural circuits.

2. Yes, people are working on this, but whether the neurons that are created are actually like the ones in a living brain require much more research. The search term for this is 'neural conversion' and the key paper is [2].

3. It is either much simpler, or much more complicated. Axons send projections along signalling gradients during development and have something akin to a lock and key system (made of cell surface proteins) that help them hit the correct targets. If you can make the signal and design the lock and key, in theory it would work. The issue of course is that we have zero idea what sticking a specific new connection in will do, though there is this paper which suggests that pure connectivity changes can have a gain of function [3]. The other area to look in for stuff related to this is axonal repair (spinal cord repair), and that is where all the theory seems to go out the window because there are so many signals that the neurons listen to. If you dig in there you will see that people have tried scaffolds, signals, stem cells, and all other manor of hocus pocus to get it to work because the search space they are in is terrifyingly huge.

0. https://en.wikipedia.org/wiki/BigBrain 1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3619199/ 2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2756723/ 3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5774341/

I don't know where you get this idea; they talk a lot about the connections between columns and how they reinforce each other.

It doesn't seem to me like they're suggesting that columns are "discontinuous" at all; On Intelligence, along with lectures Jeff Hawkins has given, describes in detail how columns are interconnected. What they describe sounds to me much more like "vertically aligned" and "closely connected" than "discontinuous."

I assume that you are referring to cortical columns aka hypercolums aka cortical modules and not cortical minicolumns?

Doesn't matter. What matters is whether the idea has engineering utility.

Jeff Hawkins is not a Biologist or a Neuroscientist (though he would probably qualify) trying to explain how the brain works. He is an Engineer using whatever bits he sees as potentially useful.

The entire premise of his research is that understanding how the brain actually works is key to developing an artificial general intelligence.

No, I think that's the route DeepMind and the rest went with. Jeff Hawkins seems to want the more biologically plausible model.

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