Electrical stimulation over the human vertebral column: which neural elements are excited?

Area of Science:

• Neuroscience
• Clinical Electrophysiology

Background:

• Percutaneous electrical stimulation over the cervical spine elicits maximal compound muscle action potentials (CMAPs).
• Identifying the specific neural elements excited by these stimuli is critical for accurate interpretation.

Purpose of the Study:

• To determine whether cervical electrical stimulation excites motor roots or other neural structures.
• To elucidate the precise neuroanatomical targets of midline cervical electrical stimulation.

Main Methods:

• Stimulation mapping with electrodes placed laterally and midline over the cervical vertebrae.
• Comparison of muscle excitation thresholds for arm versus leg muscles.
• Conduction time measurements using direct nerve stimulation and F-wave latency.
• Collision experiments with paired electrical stimuli at various nerve sites.

Main Results:

• Midline cervical stimulation produced CMAPs with latencies identical to direct stimulation near the C8 root.
• Arm muscles showed a lower excitation threshold than leg muscles with midline stimulation.
• F-wave latency exceeded direct conduction time by 1.6 msec, consistent with proximal nerve segment activation.

Conclusions:

• Midline cervical electrical stimulation directly excites motor roots as they exit the spinal canal.
• This technique provides a valuable method for assessing proximal peripheral nerve and motor root function.
• Findings have implications for clinical neurophysiology studies of the pyramidal tract and proximal nerves.