When mapping the different neural pathways in the brain, often pictures such as these are drawn:
Or similar versions. Clearly these sketches draw the neural pathways as being a two-sided connection, as can be judged from the double arrows. I was wondering, how such bidirectional pathways work. Specifically, I am interested to know whether individual neurons constitute such a bidirectional pathway between different parts of the brain, or if the bidirectional pathway can be thought of as a 'circuit': a pathway of neurons that eventually comes back to a certain part of the brain.
This question is especially interesting in light of abstract thoughts. Let's make some extremely generalising (and ludicrous) assumptions and assume that our conscious thoughts are governed by our hippocampus only. That is, we assume that thinking about a matter without input from sensory neurons causes the hippocampus to fire an action potential into some specific cluster of neurons (somewhere in the brain). E.g. we assume that thinking about the letter 'A' causes the hippocampus to fire an action potential into the cluster of neurons that represents the letter 'A'. Let's also assume that the memory we have regarding the letter 'A' must be returned to the hippocampus, in order to continue our thought process. For example, I might want to recite the alphabet in my head. Starting with the letter 'A', I then continue to the letter 'B', which arises in my conscious thoughts as a result of the firing of the cluster of neurons that contain information regarding the letter 'B'.
So if we assume the circuit, conscious thoughts $\rightarrow$ cluster of information fires $\rightarrow$ conscious thoughts to exist, then how would its feedback most likely work?
Let's take the example where we think of the letter 'A' and want to think of the letter 'B'. I have sketched two different theories about how the communication between these two clusters of information and the 'governing body of thoughts' (which I assumed to be the hippocampus), might be:
The difference is the following: in the second theory, all individual neurons are expected to be able to communicate directly to the hippocampus. Whereas in the first theory, the feedback to the hippocampus arises only when we have reached our destination: the letter 'B'. Clearly, if we assume that a specific thought process is able to self-induce action potentials (of course, this is highly debatable), at least one of the two theories must be partially true. For which one exists evidence?
My first intuition would be to say that the first theory is more likely, but this is ambiguous under Dale's principle: why would only some cells be connected to the hippocampus? On the other hand, I found it hard to believe that every individual neuron is directly connected to the hippocampus.
So now that I have explained my thought process, my question can be formulated as follows:
How are clusters of neurons that are involved in abstract thoughts bidirectionally connected to the thought-governing-body (whichever actual part(s) of the brain this is)? Can we say that just a single neuron in the cluster provides the feedback to the thought-governing-body, or is every individual neuron that is involved in conscious thought potentially capable of a feedback loop?
Disclaimer: Yes, I'm not up-to-date to all the latest advances in neuroscience. Yes, I'm aware that my question might be ambiguous with respect to all the different types of neurons, connections and theory about neuronal networks and micronetworks. My question, however, is concerning the likelihood of the theories I presented. For which one do we have evidence. Are both wrong? If so, in what way? Are both right? If so, when does their difference play a role? etc.