Differential joint-specific corticospinal tract projections within the cervical enlargement

Area of Science:

• Neuroscience
• Motor Control
• Spinal Cord Anatomy

Background:

• The motor cortex controls movement via the corticospinal tract (CST).
• Understanding CST's spinal projections is key to motor control mechanisms.
• Differential projections to spinal interneurons are hypothesized but not fully elucidated.

Purpose of the Study:

• To investigate if motor cortex sites controlling individual forelimb joints project differentially to distinct cervical spinal cord territories.
• To map CST termination fields in relation to premotor interneurons.

Main Methods:

• Identified joint-specific motor cortex sites using intracortical microstimulation.
• Traced CST terminations using anterograde tracers.
• Labeled spinal premotor interneurons via intramuscular pseudorabies virus injection.

Main Results:

• CST core terminations from shoulder, elbow, and wrist sites overlapped at C5/C6 but separated at C7/C8.
• Shoulder, elbow, and wrist sites showed preferential termination zones in the cervical spinal cord.
• CST projections were differentially organized relative to labeled premotor interneuron populations at C7/C8.

Conclusions:

• The CST exhibits fractionation in the caudal cervical enlargement, with distinct termination patterns for different forelimb joints.
• This anatomical organization may facilitate the engagement of specific spinal premotor circuits for proximal and distal limb control.