title: Stimulus waveform determines the characteristics of sensory nerve action potentials.
abstract: OBJECTIVE
  In routine nerve conduction studies supramaximal electrical stimuli generate sensory nerve action potentials by depolarization of nerve fibers under the cathode. However, stimuli of submaximal intensity may give rise to action potentials generated under the anode. We tested if this phenomenon depends on the characteristics of stimulus ending.
  
  
  METHODS
  We added a circuit to our stimulation device that allowed us to modify the end of the stimulus by increasing the time constant of the decay phase.
  
  
  RESULTS
  Increasing the fall time caused a reduction of anode action potential (anAP) amplitude, and eventually abolished it, in all tested subjects. We subsequently examined the stimulus waveform in a series of available electromyographs stimulators and found that the anAP could only be obtained with stimulators that issued stimuli ending sharply.
  
  
  CONCLUSIONS
  Our results prove that the anAP is generated at stimulus end, and depends on the sharpness of current shut down. Electromyographs produce stimuli of varying characteristics, which limits the reproducibility of anAP results by interested researchers.
  
  
  CONCLUSIONS
  The study of anodal action potentials might be a useful tool to have a quick appraisal of distal human sensory nerve excitability.
authors.affiliation: Neurology Department, Hospital Garcia de Orta, Almada, Portugal; EMG Unit, Neurology Department, Hospital Clinic, University of Barcelona, Barcelona, Spain. Electronic address: pedro.mdap@gmail.com.
authors.forename: Pedro
authors.initials: P
authors.lastname: Pereira
authors.affiliation: Neurosurgery Department, Hospital Garcia de Orta, Almada, Portugal; EMG Unit, Neurology Department, Hospital Clinic, University of Barcelona, Barcelona, Spain.
authors.forename: João
authors.initials: J
authors.lastname: Leote
authors.affiliation: EMG Unit, Neurology Department, Hospital Clinic, University of Barcelona, Barcelona, Spain.
authors.forename: Christopher
authors.initials: C
authors.lastname: Cabib
authors.affiliation: EMG Unit, Neurology Department, Hospital Clinic, University of Barcelona, Barcelona, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Casanova-Molla
authors.affiliation: EMG Unit, Neurology Department, Hospital Clinic, University of Barcelona, Barcelona, Spain.
authors.forename: Josep
authors.initials: J
authors.lastname: Valls-Sole
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D009431:Neural Conduction / Q000502:physiology*; D011984:Sensory Receptor Cells / Q000502:physiology*; D055815:Young Adult
keywords: Anode-break excitation; Double peak sensory response; Hyperpolarization-activated inward rectifying currents; Membrane excitability; Stimulus waveform