If you have been reading my posts you know that I am a firm believer in system level mechanisms.
Something system-wide is surely going to involve all the related systems working together.
A component like the Claustrum, centrally located, and with connective reach across wide swaths of brain geography, is very likely to play roles in one or more system-wide functions. The “global workspace” is one of those system-wide functions.
From my reading, I am more inclined to start at the thalamocortical interactions as a key starting point.
@Bitking: Thanks for all these materials about long-range cortico-cortical connections. I understand that your main focus was the inter-area connections between L2/3 cells.
It makes me think about the other long-range connections between areas. I have read some random papers on the topic, but didn’t find precise answers. I guess that this precise mapping is not well-known yet.
More specifically, I am looking for info on the differences between long-range:
Cortico-cortical connections in superficial vs deep layers,
and cortico-cortical vs cortico-thalamo-cortical connections (direct vs indirect pathways).
Do they project to the same area ? Are they regrouped in the same axon bundles ? Are they bidirectional ?
Do you recommend specific papers on the subject ?
PS: I came across this surprising figure from a thesis from 2010 and I am very suspicious about it:
They segregate 4 different types of cortico-cortical projecting neurons (in the visual cortex):
L3A: Short-distance feedback
L3B: Short and long-distance feedforward
L5: Short-distance feedforward
L6: Long-distance feedback
It would not fit with the hex-grid theory… but it was 8 years ago and maybe it doesn’t reflect the current understanding.
I like to conceptualize the cortical processing of a given area as agnostic of the feedforward/feedback nature of its inputs. It would make more sense!
Having read that a substantial proportion of pyramidal cells send axon collaterals to both lower and higher area, I am more inclined to think that the previous figure doesn’t reflect well the inter-area connections. Agree ?
Having read a lot since the last post, I think I have now a better view of what is going on with inter and intra-area cortical connections.
I am beginning to make some order in my notes and I chose to formalize it in a visual way to make it easier to digest, and to digitalise it to share it with you. The first slides are about those cortical connections. I am planning to do the same for a bunch of other subjects I came across…
I welcome any comment on my view on the functionality behind the inter & intra cortical connections, the speculations about the nature of representation in supra vs deep layers, and the anatomical & developmental interpretation of feedfoward/feedbak.
If the represented cortical areas have different hierarchical level, the connections are not symmetrical :
Corticocortical connections from granular to agranular tend to stop earlier in deep layers (commonly referred to as feedforwards, but this term is sometimes confusing because we like to think of the prefrontal cortex as the higher level but in fact, the main direction flows are going towards the motor cortex, see next illustration).
Corticocortical connections from agranular to granular tend to finish more in L1 (commonly referred to as feedbacks)
Those different connection patterns come from temporal differences in cortical development between agranular (early) and granular (late) areas
The feedforward pathway through the thalamus is an additional pathway completely different from this one (I am currently working on this slide).
You can have a look at this good illustration from Sherman (red arrows are the “ground truth” signal in the 3VS paper, but the predictions from L6 CT are not represented here)
Would it be accurate for me to say that by outputting the exact opposite of any input signal received as in my vesicle membrane project “I have been experimenting with the fundamental wave generating behavior of reciprocal excitatory connections found in intra-area coupling”?
I can’t help but see what looks to me like the exact same thing drawn on the surface of your illustration:
Gary, if I understand this correctly the wave action is coming from the thalamus to act as a coordinating control function with the cortical connections as the data that is being synchronized.
I am not absolutely certain on this as I have not spent enough time studying the thalamus but it looks to me that your work on waves would match up most closely with some inner working of the thalamus.
I’m trying to picture how that would work. Unfortunately the inner workings of the thalamus is still for me a complicated problem.
In the illustration the connections I’m looking at would only be the blue ones on the very surface. Everything else connected to it from below would change the behavior at that location, which in turn past that point changes the pattern of the traveling wave.
Although it’s hard to say whether it’s used as such: at the far end of each area a 2D map would become 1D signals over time, sort of a unique address that depends on what was mapped onto the 2D area. How the whiskers of an animal were brushed would show up in the complex pattern that the barrel cortex cells end up propagating outward to others, a way for each in the network area to sense unique experiences that happen in the external 3D environment.
A thought experiment for you to consider - how does the completely intermixed learned patters embedded in the cortex all play out in the same wave pattern during experience and recall? What distinguishes them one from another?
In the scheme I am proposing - the wave interrogates the contents and coordinates the sender and receiver between maps with no regard to the contents so the wave shape can be the same for both.
I can’t see how the contents form the wave; unless you can offer some explanation to tie the two mechanisms tougher I can’s see how it would work.
In this case I’m thinking more like what does a single cell that already has a good ability to predict and respond to events get out of helping to propagate 2D (stadium) waves with a pattern resembling what is being sensed happening in the external environment.
I also see it as a “wave interrogates the contents”. In the ID Lab-6 the contents would be walls bashed into and prior memories of shock zone locations at that time, which stop propagating the waves being started by the location with food in it. The waves that bounce off or adsorbed by the mind theater’s wall and avoid locations produces a vector map showing all the safe places to travel, paths towards safety.
You see that this is where the fact’s don’t support the concept. The videos that I have seen show the waves sweeping over the cortex without any diversions.
Thinking about this a little more deeply - the contents of individual maps/areas is a distributed representation. It is fair to say that the representation is really distributed up and down the entire hierarchy but I will restrict that to a single map/area for this post. There is not a local “wall” to bounce off of. The wave has to sweep across the entire map/area to do whatever processing that happens in that area of cortex. I expect that the idea of a wall is not fully formed until the wave complete a pass across the entire map/area.
I also see the processing of things like paths and goals as being far more distributed in time than a single map/area. I strongly suspect that going from perception to action involves the entire hierarchy up to the temporal lobe, a pass through the subcortical structures out to the forebrain to be elaborated into action.
The various maps/areas have to decompose the sensations into feature clouds for recognition. This model does not do things like goal selection and object avoidance in single maps/areas.
I can easily see how a very much simpler life form could do the kind of processing like the slime mold offered for example but by the time you get up to worms and insects most of the brains have evolved far past this simple model.
Totally stopping the a traveling wave would require a large number of places leaving no holes to get through, otherwise the wave goes around all obstacles. Also from what I read a barrier/boundary cell becomes active when near one, is not always active.
This would be what the navigational part of the distributed system sums up to, where there is one or many blobby representations of movement, instead of detailed picture somewhere on the cortex. To record one one the animal would have to at least in its mind be navigating a complex environment with tunnels or other features that stand out in the wave pattern.
Concerning the excitatory cells, I was referring to L5 PT and L6 CT cortical pyramidal cells that project to the thalamus, and to the miscalled thalamic “relay” cells (“miscalled” because they probably do more than a simple relay)
It seems that virtually all axons between the thalamus and the cortex give some collaterals in the TRN (which sends inhibitory inputs to thalamic relay cells and/or other inhibitory thalamic interneurons).