I’ve gone back and forth on this topic, initially being skeptical of their existence at all. I think there’s at least one CPG dump which I’ll edit in when I get the chance.
My current understanding is that CPG circuits do NOT generate or initiate salience (which is what I believe the current orthodox understanding of them is), but instead work as an organizing or synchronization region between disparate parts of an organism. They allow disparate functional regions to work at their own “clock speeds” but still be able to communicate with other regions.
In vertebrates this means a lot of translation occurs between nervous system and organs, and there’s a really convenient area where a lot of this “clock” translation occurs between brain and body. In humans, this region is usually in the medulla/lower pons.
This breaks from orthodox in stating that the purpose of CPG circuits is to coordinate signals rather than initiate them.
Second break, I don’t think there are true CPG circuits at all, but rather convenient clumps of them. Every major organ in organisms will always have it’s own set of coordinating circuits, from the heart to the sex organs. This allows the model to have relatively interdependently driven organs (and allows for modification to any organ without extensive remodeling of the CPG circuits/brain) closer to what we actually observe.
The medullary translation isn’t a master signal, but rather a convenient and efficient place to synchronize communication across organs, think of it as a noisy information bazaar where organs can tell other organs they need more or less function out of each other. Whether it’s a PDE5 inhibitor or GLP1 agonist, these drugs emulate a small slice of the methylation rate bartering going on in CPG circuits which coordinate behavior.
I’ve been super fascinated by planarians, specifically their ability to reorganize after both incision and excision. More than any other model species they probably drove the formation of the current model because of their ability to retain “memory” even after being cut. But just as fascinating as the memory aspect is that they also have the ability to re-coordinate signalling despite those CPG circuits ostensibly being destroyed.
And this led to the current model understanding that every single cell can coordinate signalling to some degree. Looking at bacteria or similar single celled colony organisms, we see exactly this type of coordination occurring with auto-inducers in quorum sensing. By sampling the chemical environment (stimuli), the cells modify their own behavior.
It works the same in all organisms, and suppressing the chemical environment stops inter-cellular coordination full stop, regardless of the organism. And this chemical rate bartering becomes the foundational element for the organization of nervous systems, with glial cells becoming specialized to barter only specific types of signals (or respond to specific types of signals) and neurons functioning as a way to reduce the noise and establish metabolically efficient signalling connections.
Summarizing a bit (because I know I’ll probably be picking at this over the next few days):
“CPG” circuits do not initiate signals, they coordinate communication between existing circuits.
Every single cell has the ability to coordinate signalling to some degree, every organ has a “clump” of specialized coordinating cells, and vertebrates have a convenient clump of clumps where organs can directly “negotiate” function.
CPG circuit communication is entirely chemical, RNA creates the message, not “electricity”.
Energy can however modify the rate of methylation, which modifies signal rate exchange.
The chemical rate exchange process is way, way, way, more complicated than you’re imagining.