“The connectivity between the cortex and the pons has been the subject of decades of study using invasive methods in non-human primates," says corresponding author Paul-Noel Rousseau, PhD Student in Concordia’s Department of Psychology and member of the Neural Architecture, Behaviour, and Connectivity Laboratory.
A team of neuroscientists at Concordia University has revealed a new organizational map of a major brain connection that supports both movement and cognition. Using advanced imaging and data-driven analysis, the researchers charted the connectivity of the of the corticopontine pathway — the first leg in a pathway linking the cerebral cortex and the cerebellum.
Their findings, recently published in Scientific Reports, are the first to document the organization of this pathway in humans. They recapitulate key findings from the non-human animal literature, showing a precise organization and highlight a potential role of the pathway in integrating information from different areas the cortex before it gets passed onto the cerebellum. It also builds upon their previously published work that mapped the connectivity of the second leg pontocerebellar pathway.
Mapping gradients, not highways
The researchers used a technique called diffusion MRI tractography, which allows for the reconstruction of white matter pathways in the living brain. But instead of focusing on distinct bundles connecting different parts of the cortex to the pons (the intermediary structure between the cortex and the cerebellum) they looked for gradual spatial patterns — or connectivity gradients — that reveal the dominant organizational patterns of this pathway.
“We find two overlapping connectivity gradients in the pons based on its connectivity from the cerebral cortex” says corresponding author Paul-Noel Rousseau, PhD Student in Concordia’s Department of Psychology and member of the Neural Architecture, Behaviour, and Connectivity Laboratory. “This shows us an ordered mapping of the cerebral cortex onto the pons in the human brain, and recapitulates findings in non-human primates that used invasive tract-tracing methods.”
The first connectivity gradient in the pons is organized in a medial to lateral direction, while the second radiates outward from a central core — a pattern the team refers to as a core-to-belt organization. When these gradients are projected back to the cortex, the first reflects an anterior to posterior organization, whereas the second radiates outward from motor areas.
From cortex to cerebellum, via a complex detour
The corticopontine pathway is the first leg of a larger loop that connects the cortex to the cerebellum, a structure long thought to be only involved in movement, but is now implicated in a wide range of cognitive and emotional processes. Understanding how the cortex connects to the pons and how cortical input is transformed on its way to the cerebellum is essential to grasping the cerebellum’s role in both movement and higher brain function.
The researchers found that their connectivity gradients were consistent across both in-vivo human and high-resolution postmortem datasets used in the study. Their approach allowed them to map their gradients along the entire length of the corticopontine pathway, and link their findings to decades of research in non-human animals.
“The connectivity between the cortex and the pons has been the subject of decades of study using invasive methods in non-human primates. Our study builds on this research in demonstrating that the organizational principles observed in this animal work also appear to apply to the human."
A new lens on an old structure
Traditionally, the pons has been viewed as a passive relay station – receiving information from the cortex and transmitting it to the cerebellum. But one of the bigger implications of the study, in its demonstration of overlapping mappings of the cerebral cortex onto this structure, suggest a more complex role. It highlights the possibility that the pons may integrate information from different areas of the cortex before it gets passed to the cerebellum. A potential computational role of the pons is an area that remains to be explored.
Senior author Christopher J. Steele, associate professor in the Department of Psychology, Principal Investigator at the Neural Architecture, Behaviour, and Connectivity Laboratory and FRQS Chercheur Boursier Junior 2, sees this as a starting point for new investigations.
“Identifying these overlapping gradients allows us to think about how information from different cortical regions may be combined to give rise to complex behaviour with the support of the cerebellum. Mapping these spatial relationships opens the door to studying how these structural connections (and/or the properties of the neural connections that underlie them) change in development, aging, or neurological disorders,” he says. “This and Paul-Noel’s other work are important steps towards understanding of the important and understudied roles of the cerebellum in the human brain.”
Toward clinical and computational insights
The findings could eventually inform models of how these pathways influence motor, cognitive, and emotional functions — and how these pathways may be disrupted in neurological and psychiatric conditions. The authors conclude by highlighting that future work, with new approaches for finer-grained reconstructions of brain connections, along with methods that look at the activity of the brain areas in question, are needed to push this research forward.
“Our study can be seen as a first approach to studying this pathway in humans,” Rousseau says. “In the future, new methods for reconstructing these connections at higher resolutions, combined with functional imaging techniques, will help further our understanding of the organization and role of this pathway.”
Learn more about research in Concordia’s Department of Psychology