I understand what you mean. I just find the terms "serial" and "parallel" too mechanical to be appropriate for what happens in a dynamic environment like the human body, as opposed to the static architecture of silicon-based computers. Those "pathways" include ones with direct links to the brain, e.g. the spinal column, Vagus nerve, and others. And then there are many interacting chemical systems, like the endocrines, etc. And complicating matters even more, we have all manner of flora and fauna in and on our bodies, e.g. gut bacteria, skin dwellers, mites. All of these produce chemicals that enter the blood stream and end up passing through the brain's blood vessels at some stage. Who knows what effects they have on a human's processing capabilities. "Serial" and "parallel" don't feel right to me to encompass all that (and the myriad things I've left out or don't know about). I don't have any idea of what might be better simple descriptors - maybe it's not possible to summarise it adequately in a word or two.