Medullary and C3-C4 propriospinal pathways underlying mammalian forelimb movement control

Area of Science:

• Neuroscience
• Motor Control
• Comparative Neuroanatomy

Background:

• Traditional models link upper limb movement to the cortex and balance to the brainstem.
• Rodent studies suggest medullary and spinal contributions to forelimb control, but human relevance is unclear.
• Interactions between cortical, medullary, and spinal circuits in hand movement are poorly understood.

Purpose of the Study:

• To investigate the corticomedullary networks regulating forelimb movement in humans and mice.
• To elucidate the dynamic interactions among cortical, medullary, and spinal motor regions during hand movement.
• To identify conserved and species-specific mechanisms of forelimb motor control.

Main Methods:

• Functional magnetic resonance imaging (fMRI) studies in humans and mice performing forelimb movement tasks.
• Simultaneous brain-spinal fMRI to map human cervical spinal cord activity.
• Analysis of corticomedullary coupling and functional connectivity within sensorimotor pathways.

Main Results:

• Identified topographically organized corticomedullary networks (lateral rostral medulla and caudal medulla) regulating forelimb movement.
• Observed species-specific patterns in corticomedullary coupling, with stronger links to motor cortices in mice and higher-order sensorimotor regions in humans.
• Revealed distinct functional territories in the human C3-C4 spinal cord, with ventral regions connected to the medulla and dorsal regions to lower cervical segments.

Conclusions:

• A conserved corticomedullary network underlies forelimb movement control across mammals.
• An indirect pathway involving the reticulospinal tract and C3-C4 propriospinal system contributes to fine hand motor control.
• Findings highlight both conserved mechanisms and variations in cortical involvement in forelimb motor control across species.