there is at least one steak neuron in my own hippocampus, and it can be stimulated by hearing the word, and persistent firing of it will cause episodic memories...to rise up
Oh yeah, I definitely agree that this is an important dynamic. I think there are two cases. In the case of episodic memory I think you’re kinda searching for one of a discrete (albeit large) set of items, based on some aspect of the item. So this is a pure autoassociative memory mechanism. The other case is when you’re forming a brand new thought. I think of it like, your thoughts are made up of a bunch of little puzzle pieces that can snap together, but only in certain ways (e.g. you can’t visualize a “falling stationary rock”, but you can visualize a “blanket made of banana peels”). I think you can issue top-down mandates that there should be a thought containing a certain small set of pieces, and then your brain will search for a way to build out a complete thought (or plan) that includes those pieces. Like “wanting to fit the book in the bag” looks like running a search for a self-consistent thought that ends with the book sliding smoothly into the bag. There might be some autoassociative memory involved here too, not sure, although I think it mainly winds up vaguely similar to belief-propagation algorithms in Bayesian PGMs.
Anyway, the hunger case could look like invoking the piece-of-a-thought:
Piece-of-a-thought X: “[BLANK] and then I eat yummy food”
…and then the search algorithm looks for ways to flesh that out into a complete plausible thought.
I guess your model is more like “the brainstem reaches up and activates Piece-of-a-thought X” and my model is more like “the brainstem waits patiently for the cortex to activate Piece-of-a-thought X, and as soon as it does, it says YES GOOD THANKS, HERE’S SOME REWARD”. And then very early in infancy the cortex learns (by RL) that when its own interoceptive inputs indicate hunger, then it should activate piece-of-a-thought X.
Maybe you’ll say: eating is so basic, this RL mechanism seems wrong. Learning takes time, but infants need to eat, right? But then my response would be: eating is basic and necessary from birth, but doesn’t need to involve the cortex. There can be a hardwired brainstem circuit that says “if you see a prey animal, chase it and kill it”, and another that says “if you smell a certain smell, bite on it”, and another that says “when there’s food in your mouth, chew it and swallow it”, etc. The cortex is for learning more complicated patterns, I think, and by the time it’s capable of doing useful things in general, it can also learn this one simple little pattern, i.e. that hunger signals imply reward-for-thinking-about-eating.
insula
FWIW, in the scheme here, one part of insular cortex is an honorary member of the “agranular prefrontal cortex” club—that’s based purely on this quote I found in Wise 2017: “Although the traditional anatomical literature often treats the orbitofrontal and insular cortex as distinct entities, a detailed analysis of their architectonics, connections, and topology revealed that the agranular insular areas are integral parts of an “orbital prefrontal network””. So this is a “supervised learning” part (if you believe me), and I agree with you that it may well more specifically involve predictions about “feeling better after consuming something”. I also think this is probably the part relevant to your comment “the insula’s supervised learning algorithms can be hacked?”.
Another part of the insula is what Lisa Feldman Barrett calls “primary interoceptive cortex”, i.e. she is suggesting that it learns a vocabulary of patterns that describe incoming interoceptive (body status) signals, analogously to how primary visual cortex learns a vocabulary of patterns that describe incoming visual signals, primary auditory cortex learns a vocabulary of patterns that describe incoming auditory signals, etc.
Those are the two parts of the insula that I know about. There might be other things in the insula too.
caudate
I didn’t explicitly mention caudate here but it’s half of “dorsal striatum”. The other half is putamen—I think they’re properly considered as one structure. “Dorsal striatum” is the striatum associated with motor-control cortex and executive-function cortex, more or less. I’m not sure how that breaks down between caudate and putamen. I’m also not sure why caudate was active in that fMRI paper you found.
hippocampus
I think I draw more of a distinction between plans and memories than you, and put hippocampus on the “memory” side. (I’m thinking roughly “hippocampus = navigation (in all mammals) and first-person memories (only in humans)”, and “dorsolateral prefrontal cortex is executive function and planning (in humans)”.) I’m not sure exactly what the fMRI task was, but maybe it involved invoking memories?
Thanks! This is very interesting!
Oh yeah, I definitely agree that this is an important dynamic. I think there are two cases. In the case of episodic memory I think you’re kinda searching for one of a discrete (albeit large) set of items, based on some aspect of the item. So this is a pure autoassociative memory mechanism. The other case is when you’re forming a brand new thought. I think of it like, your thoughts are made up of a bunch of little puzzle pieces that can snap together, but only in certain ways (e.g. you can’t visualize a “falling stationary rock”, but you can visualize a “blanket made of banana peels”). I think you can issue top-down mandates that there should be a thought containing a certain small set of pieces, and then your brain will search for a way to build out a complete thought (or plan) that includes those pieces. Like “wanting to fit the book in the bag” looks like running a search for a self-consistent thought that ends with the book sliding smoothly into the bag. There might be some autoassociative memory involved here too, not sure, although I think it mainly winds up vaguely similar to belief-propagation algorithms in Bayesian PGMs.
Anyway, the hunger case could look like invoking the piece-of-a-thought:
Piece-of-a-thought X: “[BLANK] and then I eat yummy food”
…and then the search algorithm looks for ways to flesh that out into a complete plausible thought.
I guess your model is more like “the brainstem reaches up and activates Piece-of-a-thought X” and my model is more like “the brainstem waits patiently for the cortex to activate Piece-of-a-thought X, and as soon as it does, it says YES GOOD THANKS, HERE’S SOME REWARD”. And then very early in infancy the cortex learns (by RL) that when its own interoceptive inputs indicate hunger, then it should activate piece-of-a-thought X.
Maybe you’ll say: eating is so basic, this RL mechanism seems wrong. Learning takes time, but infants need to eat, right? But then my response would be: eating is basic and necessary from birth, but doesn’t need to involve the cortex. There can be a hardwired brainstem circuit that says “if you see a prey animal, chase it and kill it”, and another that says “if you smell a certain smell, bite on it”, and another that says “when there’s food in your mouth, chew it and swallow it”, etc. The cortex is for learning more complicated patterns, I think, and by the time it’s capable of doing useful things in general, it can also learn this one simple little pattern, i.e. that hunger signals imply reward-for-thinking-about-eating.
FWIW, in the scheme here, one part of insular cortex is an honorary member of the “agranular prefrontal cortex” club—that’s based purely on this quote I found in Wise 2017: “Although the traditional anatomical literature often treats the orbitofrontal and insular cortex as distinct entities, a detailed analysis of their architectonics, connections, and topology revealed that the agranular insular areas are integral parts of an “orbital prefrontal network””. So this is a “supervised learning” part (if you believe me), and I agree with you that it may well more specifically involve predictions about “feeling better after consuming something”. I also think this is probably the part relevant to your comment “the insula’s supervised learning algorithms can be hacked?”.
Another part of the insula is what Lisa Feldman Barrett calls “primary interoceptive cortex”, i.e. she is suggesting that it learns a vocabulary of patterns that describe incoming interoceptive (body status) signals, analogously to how primary visual cortex learns a vocabulary of patterns that describe incoming visual signals, primary auditory cortex learns a vocabulary of patterns that describe incoming auditory signals, etc.
Those are the two parts of the insula that I know about. There might be other things in the insula too.
I didn’t explicitly mention caudate here but it’s half of “dorsal striatum”. The other half is putamen—I think they’re properly considered as one structure. “Dorsal striatum” is the striatum associated with motor-control cortex and executive-function cortex, more or less. I’m not sure how that breaks down between caudate and putamen. I’m also not sure why caudate was active in that fMRI paper you found.
I think I draw more of a distinction between plans and memories than you, and put hippocampus on the “memory” side. (I’m thinking roughly “hippocampus = navigation (in all mammals) and first-person memories (only in humans)”, and “dorsolateral prefrontal cortex is executive function and planning (in humans)”.) I’m not sure exactly what the fMRI task was, but maybe it involved invoking memories?