title: Jitter of corticospinal neurons during repetitive transcranial magnetic stimulation. Method and possible clinical implications.
abstract: BACKGROUND
  Repetitive transcranial magnetic stimulation (rTMS) of the motor cortex activates corticospinal neurons mainly through the depolarization of cortico-cortical axons belonging to interneurons of superficial layers.
  
  
  OBJECTIVE
  We used single-fiber electromyography (SFEMG) to estimate the "central jitter" of activation latency of interneural pools from one pulse of TMS to another.
  
  
  METHODS
  We evaluated 10 healthy subjects and one patient with multiple sclerosis. By recording SFEMG evoked activity from the left first dorsal interosseous (FDI), we first used a standard repetitive electrical 3 Hz stimulation of the ulnar nerve at the wrist to calculate the mean consecutive difference from at least 10 different potentials. The same procedure was applied during 3 Hz repetitive TMS of the contralateral motor cortex. The corticospinal monosynaptic connection of the FDI and the selectivity of SFEMG recording physiologically justified the subtraction of the "peripheral jitter" from the whole cortico-muscular jitter, obtaining an estimation of the actual "central jitter."
  
  
  RESULTS
  All subjects completed the study. The peripheral jitter was 28 μs ± 6 and the cortico-muscular jitter was 344 μs ± 97. The estimated central jitter was 343 ± 97 μs. In the patient the central jitter was 846 μs, a value more than twice the central jitter in healthy subjects.
  
  
  CONCLUSIONS
  Current results demonstrate that the evaluation of the central component of the cumulative cortico-muscular latency variability in healthy subjects is feasible with a minimally invasive approach. We present and discuss this methodology and provide a "proof of concept" of its potential clinical applicability in a patient with multiple sclerosis.
authors.affiliation: Institute of Neurology, Università Cattolica del Sacro Cuore, Rome, Italy.
authors.forename: Pietro
authors.initials: P
authors.lastname: Caliandro
authors.affiliation: Institute of Neurology, Università Cattolica del Sacro Cuore, Rome, Italy; Fondazione Don Carlo Gnocchi ONLUS, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Padua
authors.affiliation: Dipartimento di Scienze Neurologiche e Neurosensoriali, Unità di Neurologia e Neurofisiologia Clinica, Brain Investigation & Neuromodulation Lab, Azienda Ospedaliera Universitaria Senese, Policlinico Le Scotte Viale Bracci, I-53100 Siena, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Rossi
authors.affiliation: Institute of Neurology, Università Cattolica del Sacro Cuore, Rome, Italy; IRCCS S. Raffaele-Pisana, Roma, Italy; Clinica S. Raffaele, Cassino, Italy.
authors.forename: Paolo Maria
authors.initials: PM
authors.lastname: Rossini
authors.affiliation: Department of Clinical Neurophysiology, University Hospital, Uppsala, Sweden.
authors.forename: Erik
authors.initials: E
authors.lastname: Stalberg
authors.affiliation: Dipartimento di Scienze Neurologiche e Neurosensoriali, Unità di Neurologia e Neurofisiologia Clinica, Brain Investigation & Neuromodulation Lab, Azienda Ospedaliera Universitaria Senese, Policlinico Le Scotte Viale Bracci, I-53100 Siena, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Feurra
authors.affiliation: Dipartimento di Scienze Neurologiche e Neurosensoriali, Unità di Neurologia e Neurofisiologia Clinica, Brain Investigation & Neuromodulation Lab, Azienda Ospedaliera Universitaria Senese, Policlinico Le Scotte Viale Bracci, I-53100 Siena, Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: Ulivelli
authors.affiliation: Dipartimento di Scienze Neurologiche e Neurosensoriali, Unità di Neurologia e Neurofisiologia Clinica, Brain Investigation & Neuromodulation Lab, Azienda Ospedaliera Universitaria Senese, Policlinico Le Scotte Viale Bracci, I-53100 Siena, Italy.
authors.forename: Sabina
authors.initials: S
authors.lastname: Bartalini
authors.affiliation: Dipartimento di Scienze Neurologiche e Neurosensoriali, Unità di Neurologia e Neurofisiologia Clinica, Brain Investigation & Neuromodulation Lab, Azienda Ospedaliera Universitaria Senese, Policlinico Le Scotte Viale Bracci, I-53100 Siena, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Giannini
authors.affiliation: Dipartimento di Scienze Neurologiche e Neurosensoriali, Unità di Neurologia e Neurofisiologia Clinica, Brain Investigation & Neuromodulation Lab, Azienda Ospedaliera Universitaria Senese, Policlinico Le Scotte Viale Bracci, I-53100 Siena, Italy. Electronic address: rossisimo@unisi.it.
authors.forename: Simone
authors.initials: S
authors.lastname: Rossi
mesh_terms: D000328:Adult; D001369:Axons / Q000502:physiology; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007395:Interneurons / Q000502:physiology; D008297:Male; D009044:Motor Cortex / Q000166:cytology* / Q000502:physiology; D009103:Multiple Sclerosis / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult
keywords: Evoked potential; Jitter; Motor tract; Single fiber; Transcranial magnetic stimulation