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Although it does not exactly follow in response to your post, the topic of daydreams led me to contemplate the role of input and output in a trail of thoughts.  Sometimes as I daydream or just think about some topic, I seem to go from one idea to another and then another and so on, and by the time I reach my final thought I often am not able to remember how I that idea once originated from my initial idea. 

A trail of thoughts can be considered to be a series of inputs and outputs with each output essentially becoming a new input for the next output.  Each input has the ability to lead to a few different outputs, and as one is choosen, a certain path is created just as a path is created in the box diagrams.  Input A leads to some output, and then that output leads to some other output.  Thus, you can trace from one thought to the next, just as you can trace from one input to the next input/output.  However, if you look at the final output and the initial input without looking at the middle section, it is often difficult to understand how you arrived at that output and thus you must trace backwards from the output or trace forwards from the input. 

Such seems to occur for daydreams/thought trains as well.  It is often difficult to understand how idea A somehow turned into idea Z.  Therefore, you have to trace backwards from idea Z figuring out what idea lead to the next until you come to the original idea A.  Although these mixes trail of thoughts are not trails of neurons, they can be thought of as similar to these neurons that produce box diagrams with inputs and outputs that may or maynot need or produce the other in that output B may not need input A in order to be produced.  For example, an idea might have come from a previous idea, but that previous idea maynot be needed in order to produce this idea, another different idea might have been able to produce it or maybe no input from the external world, no idea was needed.  Thus, just as the nervous system should not be thought of as a stimulus response, this thought trail should not be thought of as a stimulus response as well.  Thought trails resemble the nervous system.