Question/Seeking sources on "Every part of the neocortex generates movement"

I’m reading 1000 brains and the mentions of how “every part of the neocortex generates movement” are extremely compelling to me!

On page 18 Hawkins discusses how every part of the neocortex projects to some part of the brain related to movement and that there are no pure motor regions and no pure sensory regions.

I’m familiar with some of this literature and previous research on layer 5. but since there are not citations I would love any paper recommendations or anyone’s thoughts on this topic and how they interpret its implications. that said “every part of the neocortex generates movement” seems like a pretty significant claim and I’m wondering if it can be extended to / should be interpreted as that all neocortical activity has some form of motor output (perhaps often incredibly subtle / sub-perceptual )

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The keyword is ‘pure’ in that there are no pure motor regions and no pure sensory regions from the standpoint of boundaries. The neural network fans out and intersects so that you just cannot go in and slice out the sections that make your lips move or allows your fingertips to sense heat. That is my take on this, but I also would like to see some seminal papers that specifically discuss it.

I cant direct you to specific literature. However my guess would be to look into literature of V1 visual cortex.

In my thinking, this statement says, that every part of the cortex extracts some movement, that may be used to move the body. Therefore it might be hard to find direct evidence, that V1 directly drives some muscle cells. But as a collective, V1 could be important to signal shifts of the whole visual scene, for example due to a external change in the environment, which could trigger a eye/head movement correcting the scene back to the original place on the retina.

And because this might be very subtle, it might be hard to finger point evidence onto individual cells. Correlations however might not be enough to convince some people.
However as we want to understand the cortical algorithm, I find it not so important, that the output of every cortical column really is used. Much more important is a theory, that explains most of it and provides a reason for the connectivity of L5 cells.

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I haven’t really dived into this but it’s an area I find interesting and important and confusing.

I’ll focus on one particular example: As far as I understand, there are connections from primary visual cortex (V1) to the superior colliculus (SC), arranged topographically—i.e. the parts that analyze the same part of the visual field are wired together.

As you mention, Jeff has long said these connections are the cortex sending motor commands (superior colliculus is involved in moving the eyes / saccades, in addition to sensory processing). A new paper from S. Murray Sherman and W. Martin Usrey also says that these connections are motor commands. I don’t know who else thinks that, those are the only two places I’ve seen it.

Again I haven’t thought it too much, but right now I generally don’t like this theory. For one thing, my understanding is that V1 is not set up with the cortico-basal ganglia-thalamo-cortical loops that the brain uses for RL, and I normally think you need RL to learn motor control. For another thing, aren’t the frontal eye fields in charge of saccades?? (At least, in charge at the cortical level.) For yet another thing, it seems to me that “V1 cortical column #832” is not in a good position to know whether saccading to the corresponding part of the visual field is a good or bad idea. The decision of where and when to saccade needs to incorporate things like “what am I trying to do”, “what’s going on in general”, “what has high value-of-information”, etc.—information that I don’t think a particular V1 column would have.

The closest thing to motor control theory that kinda makes sense to me is a “Confusing things are happening here” message . More specifically, each V1 column ought to “know” if it’s the case that higher-level models keep issuing confident predictions about what’s gonna happen at that part of the visual field, and those predictions keep being falsified. So when that happens, it could send a “Confusing things are happening here” message to SC.

Those messages would not be exactly a motor command per se , but the SC could reasonably act on the information by saccading to the confusing area. So then the messages wind up being more-or-less a motor command in effect.

Then here’s one more alternative theory I was thinking about. There’s a thing where if there’s a sudden flashing light, we immediately saccade to it, and maybe do other orienting reactions like move our head and body (and maybe also release cortisol etc.). My impression is that it’s SC that decides that this reaction is appropriate, and that orchestrates it.

But if we expect the flashing light, we’ll be less likely to orient to it.

So maybe the V1 → SC axons are saying: “Hey SC, there’s about to be motion in this particular part of the visual field. So if you see something there, it’s fine, chill out, we don’t have to orient to it.”

I don’t know which of those three ideas (or something else entirely) is the real explanation, and again I haven’t looked into it too much, but I’m happy for an excuse to chat about it. :smiley:

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Keep in mind that the projections from a column don’t necessarily have to go to drive muscle.
They can project to other areas (the distance communication mentioned briefly in passing in the book) and influence other areas of the cortex as a “muscle” output.

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Mouse S1 L5 projects to spinal cord for muscles and sensory modulation [1].

I think L5 is probably a location-related signal. See [2] for an example of L5 representing location. Location is at the intersection of motor and sensory. If L5 represents location-related info, it might tend to generate motor output from a given cortical region, because having another reference frame is useful for motor control. That wouldn’t mean it always generates motor output.

There are other areas which generate a saccade when stimulated electrically, like LIP.

Maybe via the projections from basal ganglia to superior colliculus and then from superior colliculus to LGN to V1. I don’t know much about basal ganglia though.

[1] https://academic.oup.com/cercorcomms/article/1/1/tgaa052/5894594
This source is mainly about S1 projecting to part of spinal cord for sensory modulation, but it says it mainly projects to another part which I think is for muscles.
Also see https://onlinelibrary.wiley.com/doi/abs/10.1002/mus.20333. They speculate that corticospinal projections didn’t first evolve for directly controlling muscles. Whereas humans have major problems if the corticospinal tract is damaged, animals like rodents don’t have such obvious impairments. Instead of not being able to walk, they have problems with motor tasks which require responding to sensory input, like holding things with paws.
Maybe in general, the cortex doesn’t produce motor commands like “move left”, but rather does stuff indirectly related to behaviors, like saccade target identification or proprioception stuff. Maybe conscious motor control is a specialization, and we shouldn’t think of L5 as representing motor commands.

[2] Independent representations of self-motion and object location in barrel cortex output
In a part of primary cortex, L5 represents object location relative to something besides the sensory organ, e.g. the head or body. There’s a lot of papers on the topic, e.g. their source 42. L5 is probably creating the location representation, not getting it from elsewhere, since it involves apical calcium event coincidence detection shenanigans.
Although, in L2/3 there’s something like a smooth map of the space around the head, so L5 might not create it. I vaguely recall the apical calcium events being specific to L5tt cells, but those calcium events might be about something else, like attention or realizing a location. See Surround Integration Organizes a Spatial Map during Active Sensation - ScienceDirect, and there’s interesting looking newer papers citing it in google scholar. I forget what L5 is like in that. Also, this is kinda a unique challenge for whiskers since they feel things by forces at their base, more indirect than vision and touch. It needs to convert to some other space or it’d look like things are moving (whiskers move back and forth many times each second). This could all be unique to the whisker system.

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Hey @Mackenzie! I brought this up at a team meeting and Jeff said that this insight came from personal conversations with Murray Sherman. He recommended reading Murray’s book “Exploring the Thalamus and its Role in Cortical Function” as a starting point. Our team also suggested watching this talk Murray gave. You might also find our blog on the Thalamus Snubbed helpful.

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