Thanks for clarifying. The point where I’m at now is, as I said in my previous comment,
if it’s just signal strength, rather than signal speed, why bring “A” [cortico-cortical connections] into it, why not just have “B” [“quasi-volitional” connections] and “C” [“perceptual” connections]?
Hmm, this seems really obvious to me, so maybe we’re talking past each other somehow.
In this oversimplified picture, we’re supposing that somatosensory cortex is tasked with trying to figure out exactly where and how the arm will be moving in the immediate future.
How does the somatosensory cortex do that? Well, it takes whatever input data it has access to, and builds a (very-short-term) predictive model that leverages that data.
The input data is critical. In general, in life, you can’t make predictions if you have absolutely nothing to go on. If you ask me to predict who’s going to win the football match, but don’t tell me which teams are playing, then all I can do is guess randomly. If you tell me the teams, I can do a bit better; if you tell me their records so far this season, I can do even better; if you tell me which players are injured today, then I can do better yet; etc. More relevant input data enables better predictions.
Anyway, what’s the input data that the somatosensory cortex can use for its predictions? Well, visual data is helpful—maybe you see that your hand is heading towards a wall. Proprioceptive data is obviously helpful—for example, if the arm is already fully extended then you can be confident that it won’t extend further. And then there’s data from all sorts of random slow interoceptive fibers, like muscle strain sensors or whatever. All that data and more is good and helpful for the somatosensory cortex to issue accurate predictions of exactly where and how the arm will be moving in the immediate future.
…But those predictions are still going to be way off if the somatosensory cortex isn’t getting any data indicating what motor cortex is up to. Like, let’s say some part of motor cortex decides it’s a good time to move my arm, and then starts sending appropriate signals to motoneuron pools or whatever. But also assume there’s no data going from motor cortex to somatosensory cortex. Then obviously the somatosensory cortex would have no idea what the motor cortex is up to, and would issue very bad predictions regarding how my arm is about to move. Right?
I agree that the somatosensory cortex [in the case of arm movements, actually mostly the parietal cortex, but also somewhat the somatosensory] needs to be getting information from the motor cortex [actually mostly the DLPFC, but also somewhat the motor] about what to expect the arm to do!
This necessary predictive-processing “attenuate your sensory input!” feedback signal, could be framed as “A [C]”, such that “weak A [C]” might start giving you hallucinations.
However, in order for the somatosensory cortex to notice a prediction error and start hallucinating, it has to be receiving a stronger [let’s say “D”] signal, from the arm, signifying that the arm is moving, than the “weak A [C]” signal signifiying that we moved the arm.
I don’t think your theory predicts this or accounts for this anyhow?
My “Q/P” theory does.
[ “B” in your theory maps to my “quasi-volition”, ie anterior cortex, or top-down cortical infrastructure.
Every other letter in your theory—the “A”, “C”, and “D”—all map to my “perception”, ie posterior cortex, or bottom-up cortical infrastructure. ]
Thanks for clarifying. The point where I’m at now is, as I said in my previous comment,
Hmm, this seems really obvious to me, so maybe we’re talking past each other somehow.
In this oversimplified picture, we’re supposing that somatosensory cortex is tasked with trying to figure out exactly where and how the arm will be moving in the immediate future.
How does the somatosensory cortex do that? Well, it takes whatever input data it has access to, and builds a (very-short-term) predictive model that leverages that data.
The input data is critical. In general, in life, you can’t make predictions if you have absolutely nothing to go on. If you ask me to predict who’s going to win the football match, but don’t tell me which teams are playing, then all I can do is guess randomly. If you tell me the teams, I can do a bit better; if you tell me their records so far this season, I can do even better; if you tell me which players are injured today, then I can do better yet; etc. More relevant input data enables better predictions.
Anyway, what’s the input data that the somatosensory cortex can use for its predictions? Well, visual data is helpful—maybe you see that your hand is heading towards a wall. Proprioceptive data is obviously helpful—for example, if the arm is already fully extended then you can be confident that it won’t extend further. And then there’s data from all sorts of random slow interoceptive fibers, like muscle strain sensors or whatever. All that data and more is good and helpful for the somatosensory cortex to issue accurate predictions of exactly where and how the arm will be moving in the immediate future.
…But those predictions are still going to be way off if the somatosensory cortex isn’t getting any data indicating what motor cortex is up to. Like, let’s say some part of motor cortex decides it’s a good time to move my arm, and then starts sending appropriate signals to motoneuron pools or whatever. But also assume there’s no data going from motor cortex to somatosensory cortex. Then obviously the somatosensory cortex would have no idea what the motor cortex is up to, and would issue very bad predictions regarding how my arm is about to move. Right?
I agree that the somatosensory cortex [in the case of arm movements, actually mostly the parietal cortex, but also somewhat the somatosensory] needs to be getting information from the motor cortex [actually mostly the DLPFC, but also somewhat the motor] about what to expect the arm to do!
This necessary predictive-processing “attenuate your sensory input!” feedback signal, could be framed as “A [C]”, such that “weak A [C]” might start giving you hallucinations.
However, in order for the somatosensory cortex to notice a prediction error and start hallucinating, it has to be receiving a stronger [let’s say “D”] signal, from the arm, signifying that the arm is moving, than the “weak A [C]” signal signifiying that we moved the arm.
I don’t think your theory predicts this or accounts for this anyhow?
My “Q/P” theory does.
[ “B” in your theory maps to my “quasi-volition”, ie anterior cortex, or top-down cortical infrastructure.
Every other letter in your theory—the “A”, “C”, and “D”—all map to my “perception”, ie posterior cortex, or bottom-up cortical infrastructure. ]