medial hypothalamus neuron groups are mostly “tracking a state variable”;
lateral hypothalamus neuron groups are mostly “turning on a behavior” (especially a “consummatory behavior”).
(…apart from the mammillary areas way at the posterior end of the hypothalamus. They’re their own thing.)
State variables are things like hunger, temperature, immune system status, fertility, horniness, etc.
I don’t have a great proof of that, just some indirect suggestive evidence. (Orexin, contiguity between lateral hypothalamus and PAG, various specific examples of people studying particular hypothalamus neurons.) Anyway, it’s hard to prove directly because changing a state variable can lead to taking immediate actions. And it’s really just a rule of thumb; I’m sure there’s exceptions, and it’s not really a bright-line distinction anyway.
The literature on the lateral hypothalamus is pretty bad. The main problem IIUC is that LH is “reticular”, i.e. when you look at it under the microscope you just see a giant mess of undifferentiated cells. That appearance is probably deceptive—appropriate stains can reveal nice little nuclei hiding inside the otherwise-undifferentiated mess. But I think only one or a few such hidden nuclei are known (the example I’m familiar with is “parvafox”).
Yeah, the word “consummatory” isn’t great in general (see here), maybe I shouldn’t have used it. But I do think walking is an “innate behavior”, just as sneezing and laughing and flinching and swallowing are. E.g. decorticate rats can walk. As for human babies, they’re decorticate-ish in effect for the first months but still have a “walking / stepping reflex” from day 1 I think.
There can be an innate behavior, but also voluntary cortex control over when and whether it starts—those aren’t contradictory, IMO. This is always true to some extent—e.g. I can voluntarily suppress a sneeze. Intuitively, yeah, I do feel like I have more voluntary control over walking than I do over sneezing or vomiting. (Swallowing is maybe the same category as walking?) I still want to say that all these “innate behaviors” (including walking) are orchestrated by the hypothalamus and brainstem, but that there’s also voluntary control coming via cortex→hypothalamus and/or cortex→brainstem motor-type output channels.
I’m just chatting about my general beliefs. :) I don’t know much about walking in particular, and I haven’t read that particular paper (paywall & I don’t have easy access).
I’ve long had a tentative rule-of-thumb that:
medial hypothalamus neuron groups are mostly “tracking a state variable”;
lateral hypothalamus neuron groups are mostly “turning on a behavior” (especially a “consummatory behavior”).
(…apart from the mammillary areas way at the posterior end of the hypothalamus. They’re their own thing.)
State variables are things like hunger, temperature, immune system status, fertility, horniness, etc.
I don’t have a great proof of that, just some indirect suggestive evidence. (Orexin, contiguity between lateral hypothalamus and PAG, various specific examples of people studying particular hypothalamus neurons.) Anyway, it’s hard to prove directly because changing a state variable can lead to taking immediate actions. And it’s really just a rule of thumb; I’m sure there’s exceptions, and it’s not really a bright-line distinction anyway.
The literature on the lateral hypothalamus is pretty bad. The main problem IIUC is that LH is “reticular”, i.e. when you look at it under the microscope you just see a giant mess of undifferentiated cells. That appearance is probably deceptive—appropriate stains can reveal nice little nuclei hiding inside the otherwise-undifferentiated mess. But I think only one or a few such hidden nuclei are known (the example I’m familiar with is “parvafox”).
plausible...but surely walking isn’t “consummatory”? And turning on the DBS doesn’t cause “automatic/involuntary” walking movements.
Yeah, the word “consummatory” isn’t great in general (see here), maybe I shouldn’t have used it. But I do think walking is an “innate behavior”, just as sneezing and laughing and flinching and swallowing are. E.g. decorticate rats can walk. As for human babies, they’re decorticate-ish in effect for the first months but still have a “walking / stepping reflex” from day 1 I think.
There can be an innate behavior, but also voluntary cortex control over when and whether it starts—those aren’t contradictory, IMO. This is always true to some extent—e.g. I can voluntarily suppress a sneeze. Intuitively, yeah, I do feel like I have more voluntary control over walking than I do over sneezing or vomiting. (Swallowing is maybe the same category as walking?) I still want to say that all these “innate behaviors” (including walking) are orchestrated by the hypothalamus and brainstem, but that there’s also voluntary control coming via cortex→hypothalamus and/or cortex→brainstem motor-type output channels.
I’m just chatting about my general beliefs. :) I don’t know much about walking in particular, and I haven’t read that particular paper (paywall & I don’t have easy access).