Inflections in threshold electrotonus to depolarizing currents in sensory axons.
Threshold electrotonus involves tracking the changes in axonal excitability produced by subthreshold polarizing currents and is the only technique that allows insight into the function of internodal conductances in human subjects in vivo. There is often an abrupt transient reversal of the threshold change as excitability increases in response to conditioning depolarizing currents (S1 phase). In recordings from motor axons, it has been recently demonstrated that this notch or inflection is due to activation of low-threshold axons. We report that a notch is frequently seen in sensory recordings (in 33 of 50 healthy subjects) using the standard threshold electrotonus protocol. When large, the notch can distort subsequent phases of threshold electrotonus and could complicate quantitative measurements and modeling studies.
Burke
David
D
Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, University of Sydney, Sydney, NSW 2006, Australia. d.burke@med.usyd.edu.au
Howells
James
J
Trevillion
Louise
L
Kiernan
Matthew C
MC
Bostock
Hugh
H
D000200:Action Potentials / Q000502:physiology*; D016477:Artifacts; D001369:Axons / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology; D003951:Diagnostic Errors / Q000517:prevention & control; D004558:Electric Stimulation / Q000379:methods; D004594:Electrophysiology; D006801:Humans; D008564:Membrane Potentials / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology; D009431:Neural Conduction / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology*; D010525:Peripheral Nerves / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology*