It would help me to shape my picture of the brain, if I knew the following:
Consider two specified groups of neurons A and B in the brain that are well-located but quite distant from each other (e.g. two roughly spherical nuclei, or two Brodman areas corresponding across hemispheres), and which are (more or less) directly connected synaptically, i.e. axons of the first group build synapses with dendrites of the second, the distance being mainly bridged by the axons. I assume there are lots of examples on different scales.
My question is: Is there a preferred way how the axons are organized, i.e. spatially distributed in the brain? Do they run mostly parallel to each other in bundles, or are there (maybe exceptional) cases, where the axons (or small subsets of axons) take individual routes, possibly quite far from each other?
I am aware that with intermediate groups of neurons, there are different and non-parallel pathways of one group of neurons to the other. So my question is explicitly about directly connected groups.
(Are there too many simplifying assumptions in my question that make it vacuous?)