Interregional connections (e.g. parietal lobe to prefrontal lobe, or V1 to V2) are fewer, and consistent enough between different people, and involve many fewer total connections, so they’ve all been pretty well described by modern neuroscience.
Wait are you saying that not only there is quite low long-distance bandwidth, but also relatively low bandwith between neighboring areas? Numbers would be very helpful.
And if there’s much higher bandwidth between neighboring regions, might there not be a lot more information that’s propagating long-range but only slowly through intermediate areas (or would that be too slow or sth?)?
(Relatedly, how crisply does the neocortex factor into different (specialized) regions? (Like I’d have thought it’s maybe sorta continuous?))
I’m glad you’re curious to learn more!
The cortex factors quite crisply into specialized regions. These regions have different cell types and groupings, so were first noticed by early microscope users like Cajal.
In a cortical region, neurons are organized first into microcolumns of 80-100 neurons, and then into macrocolumns of many microcolumns.
Each microcolumn works together as a group to calculate a function. Neighboring microcolumns inhibit each other. So each macrocolumn is sort of a mixture of experts.
The question then is how many microcolumns from one region send an output to a different region. For the example of V1 to V2, basically every microcolumn in V1 sends a connection to V2 (and vise versa). This is why the connection percentage is about 1%. 100 neurons per microcolumn, 1 of which has a long distance axon to V2. The total number of neurons is roughly 10 million, organized into about 100,000 microcolumns.
For areas that are further apart, they send fewer axons. Which doesn’t mean their signal is unimportant, just lower resolution. In that case you’d ask something like “how many microcolumns per macrocolumn send out a long distance axon from region A to region B?” This might be 1, just a summary report of the macrocolumn. So for roughly 10 million neurons, and 100,000 microcolumns organized into around 1000 macrocolumns… You get around 1000 neurons send axons from region A to region B.
More details are in the papers I linked elsewhere in this comment thread.
Yeah I believe what you say about that long-distance connections not that many.
I meant that there might be more non-long-distance connections between neighboring areas. (E.g. boundaries of areas are a bit fuzzy iirc, so macrocolumns towards the “edge” of a region are sorta intertwined with macrocolumns of the other side of the “edge”.) (I thought when you mean V1 to V2 you include those too, but I guess you didn’t?)
Do you think those inter-area non-long-distance connections are relatively unimportant, and if so why?
Wait are you saying that not only there is quite low long-distance bandwidth, but also relatively low bandwith between neighboring areas? Numbers would be very helpful.
And if there’s much higher bandwidth between neighboring regions, might there not be a lot more information that’s propagating long-range but only slowly through intermediate areas (or would that be too slow or sth?)?
(Relatedly, how crisply does the neocortex factor into different (specialized) regions? (Like I’d have thought it’s maybe sorta continuous?))
I’m glad you’re curious to learn more! The cortex factors quite crisply into specialized regions. These regions have different cell types and groupings, so were first noticed by early microscope users like Cajal. In a cortical region, neurons are organized first into microcolumns of 80-100 neurons, and then into macrocolumns of many microcolumns. Each microcolumn works together as a group to calculate a function. Neighboring microcolumns inhibit each other. So each macrocolumn is sort of a mixture of experts. The question then is how many microcolumns from one region send an output to a different region. For the example of V1 to V2, basically every microcolumn in V1 sends a connection to V2 (and vise versa). This is why the connection percentage is about 1%. 100 neurons per microcolumn, 1 of which has a long distance axon to V2. The total number of neurons is roughly 10 million, organized into about 100,000 microcolumns.
For areas that are further apart, they send fewer axons. Which doesn’t mean their signal is unimportant, just lower resolution. In that case you’d ask something like “how many microcolumns per macrocolumn send out a long distance axon from region A to region B?” This might be 1, just a summary report of the macrocolumn. So for roughly 10 million neurons, and 100,000 microcolumns organized into around 1000 macrocolumns… You get around 1000 neurons send axons from region A to region B.
More details are in the papers I linked elsewhere in this comment thread.
Thanks!
Yeah I believe what you say about that long-distance connections not that many.
I meant that there might be more non-long-distance connections between neighboring areas. (E.g. boundaries of areas are a bit fuzzy iirc, so macrocolumns towards the “edge” of a region are sorta intertwined with macrocolumns of the other side of the “edge”.)
(I thought when you mean V1 to V2 you include those too, but I guess you didn’t?)
Do you think those inter-area non-long-distance connections are relatively unimportant, and if so why?