Surface anodal stimulation of human peripheral nerves

Area of Science:

• Neuroscience
• Electrophysiology

Background:

• Bipolar surface stimulation of peripheral nerves can activate nerve fibers.
• Understanding the precise mechanisms of activation at both cathode and anode is crucial for accurate electrodiagnostic testing.

Purpose of the Study:

• To investigate the characteristics of action potentials elicited by bipolar surface stimulation of human peripheral nerves.
• To clarify the contributions of cathodal and anodal stimulation to recorded nerve action potentials.
• To highlight the implications of stimulation polarity on neurography interpretations.

Main Methods:

• Utilized bipolar surface stimulation with short square pulses on human peripheral nerves.
• Recorded nerve action potentials using a bipolar surface electrode positioned on the anodal side relative to the stimulating electrode.
• Varied stimulus strength to observe changes in recorded responses.

Main Results:

• Both cathodal and anodal stimulation initiated action potentials in A-alpha fibers.
• Medium strength stimulation resulted in a double-peaked response, with long latency (cathode) and short latency (anode) peaks.
• Strong stimulation predominantly recorded the short latency anodal peak, while weak stimulation recorded the long latency cathodal peak.

Conclusions:

• Stimulus polarity significantly influences recorded nerve action potentials and their latencies.
• Misinterpretation of polarity can lead to errors in calculating nerve conduction velocities, F-responses, and somatosensory evoked potentials (SEPs).
• Dual-peak responses may be erroneously attributed to anomalous innervation or specific axon subpopulations.