I think there's a significant difference worth illustrating that "there is no feedback path in the brain" is not at all equivalent to "learning by feedback is n

I think there's a significant difference worth illustrating that "there is no feedback path in the brain" is not at all equivalent to "learning by feedback is not possible in the brain." It's well known in dynamics that feed-forward networks are no longer feed-forward when outputs are coupled to inputs, an example of which would be a hypothetically feed-forward network of neurons in an animal and environmental conditioning teaching it the consequences of actions. I'm very curious on the biological constraints, but I'd reiterate my point above that feedback is a mathematical or logical abstraction for analyzing the behavior of the things we call networks - which are also abstractions. There's a distinction between the physical behavior of the things we see and the mathematical models we construct to describe them, like electromechanical systems where physically no such coupling from output-to-input appears to exist, yet its existence is crucially important analytically.