Segregated parallel inputs to the brachial spinal cord from the cingulate motor cortex in the monkey

Area of Science:

• Neuroscience
• Motor Control
• Primate Anatomy

Background:

• The cingulate motor cortex plays a role in motor control.
• Understanding its projections to the spinal cord is crucial for deciphering motor pathways.
• Specific areas M3 and M4 are implicated in motor functions.

Purpose of the Study:

• To investigate the corticospinal projection patterns from the arm representations of M3 (area 24c) and M4 (area 23c) to the lower cervical spinal cord (C5-T1).
• To determine if these projections target distinct or overlapping regions within the spinal gray matter.

Main Methods:

• Injection of biotinylated dextran amine into the arm representations of M3 or M4 in four rhesus monkeys.
• Anatomical tracing of anterograde axonal transport to visualize terminal fields in the spinal cord.
• Microscopic analysis of labeled terminal locations within specific spinal cord laminae.

Main Results:

• Corticospinal projections from M3 primarily targeted the lateral aspects of spinal laminae V, VI, IV, and VII, and lamina IX.
• In contrast, projections from M4 predominantly innervated the medial parts of spinal laminae III, IV, V, VI, VII, X, and lamina IX.
• These results demonstrate spatially segregated termination zones for M3 and M4 projections within the cervical spinal cord.

Conclusions:

• The arm representations of M3 and M4 project to distinct and separate areas of the spinal gray.
• These findings suggest that the two cingulospinal systems may mediate independent and specialized aspects of upper limb movement control.
• This highlights a potential functional differentiation within the cingulate motor cortex's spinal projections.