Connectivism and axon guidance

After watching this video on neurite outgrowth from garlandscience, I cannot help but think that graphs are too clean and neutral as a visualizing tool for connectivist learning.

What I came to learn about growth cones and axon guidance is that first, axons has a synaptic target.  It means that they select what they connect to.  They don't just randomly connect to whatever neuron is nearby.

But then how do they establish a target in the first place? The axon guidance article in Wikipedia states that they "'sniff out' the extracellular environment for signals that instruct the axon which direction to grow" and that there are specific molecules in the extracellular environment that repel or attract the axon growth.

This doesn't answer my question.  It just says that the axon moves left or right etc. given some mollecules in the environment.  But the articles are silent in how the environment in the brain is regulated, that is, what increases a particular repulsive molecule in a certain area and an attractive molecule in another.  The lab experiments seem to be injecting these molecules in vitro rather than observing their production in their natural setting.

In connectivist learning, the role of a curator or someone who can guide another person towards a node/actor/vector is important.  It filters the environment, thereby playing the role of the unknown agent that produces repulsive and attractive cues.  A person may recommend a website as a resource for a particular research or dissuade others from reading another website.

An interesting idea to me is the fact that human beings can set targets or goals, and can change those as they sniff the environment.  Can neurons do the same, can they set themselves to targetting a another neuron that has a specific amount of molecules or other attributes?  The neurons that have outgrowths that connect to cells in the eyes, nose, ears etc. seems to have predetermined targets.  How do we separate this kind of connection with connection due to learning in the brain in relation to an analogy for the social and conceptual mode in connectivism?