Mapping the Rest of the Human Connectome

December 17, 2020

Studying the connectivity of the brain has been a central area of study across many research institutions. 

But what about the rest of the nervous system? 

A ‘connectome’ is defined as an extensive map of neural connections in the brain. 

Jack Van Horn, Professor at the School of Data Science and in the Department of Psychology at UVA, wants to change that definition to include more than just the brain. 

“The ‘connectome’ represents the complete set of white matter fiber connections in the brain. The term ‘connectome’ is often used to refer to the connectivity of the central nervous system (CNS) – that is the brain, cerebellum, and brain stem,” Van Horn explained. “However, for as much of the human nervous system that lies inside the head, there is that much again which lies outside of it.”

Van Horn refers to these neural connections as the information superhighways of the brain.

Van Horn decided to team up with Andrei Irimia, a neuroscientist and professor of Gerontology at the University of Southern California to look further into this topic. 

Prior to working at UVA, Van Horn worked on the Human Connectome Project (HCP) collaborative project involving research team’s based at Massachusetts General Hospital and at the University of Southern California.

“This involved the development of advanced neuroimaging technologies and data processing methods to examine the brain’s white matter connectivity,” Van Horn said of the project. “Over the past decade, the HCP, and it’s various derivatives, has become one of the most important NIH programs to examine the structure, function, and connectivity of the human central nervous system.”

After working on this project, Van Horn knew he wanted to continue this research on an extensive human connectome. 

Van Horn and Irimia argue that a true human connectome requires mapping the entire spinal cord (SC) and peripheral nervous system (PNS) in addition to the brain. 

The PNS is made up of the nerves outside of the brain and spinal cord. 

“This peripheral nervous system (PNS) includes the cranial nerves, spinal cord (SC), those nerves controlling our internal organs, and all the nerves which reach to our fingertips and toes.  Under the HCP, the PNS was not considered.  Mapping the PNS, in addition to the CNS, represents the ‘full’ human connectome.”

As Van Horn and Irimia state in their research, the implications for such extensive mapping of the SC and PNS could be widespread in research and clinical use. 

“Numerous clinical disorders affect the SC and PNS, directly or indirectly,” Van Horn explained. “These include things like motor neurone disease (e.g. Lou Gerig’s Disease), diabetic neuropathy, Guillain-Barre Syndrome, gut motility disorders like Achalasia, among others. Being able to use modern medical imaging to map the brain’s white matter architecture in concert with the extensive connectivity of the PNS would provide improved context, diagnostic characterizations, and help to guide treatment options.”

In their publication about this research, they note that this is the next necessary step in neuroimaging science.

“The atlasing of these complete neural structures is essential for neurosurgical planning, neurological localization, and for mapping those components of the human connectome located outside of the CNS” (NeuroImage).

To fill this knowledge gap in neural connectivity mapping, Van Horn and Irimia advocate for a full connectome atlas, which would outline the entire human nervous system. 

Van Horn explained that this will not be an easy task. 

“Mapping these pathways is a computationally intensive task, often involving terabytes of brain imaging data across multiple subjects, using big computers, image processing, and network theoretical mathematics,” he noted. “The brain is a major data science challenge.”

To learn more, see their recent publication in NeuroImage here