title: Effect of coil orientation on strength-duration time constant and I-wave activation with controllable pulse parameter transcranial magnetic stimulation.
abstract: OBJECTIVE
  To compare the strength-duration (S-D) time constants of motor cortex structures activated by current pulses oriented posterior-anterior (PA) or anterior-posterior (AP) across the central sulcus.
  
  
  METHODS
  Motor threshold and input-output curve, along with motor evoked potential (MEP) latencies, of first dorsal interosseus were determined at pulse widths of 30, 60, and 120 μs using a controllable pulse parameter (cTMS) device, with the coil oriented PA or AP. These were used to estimate the S-D time constant and we compared with data for responses evoked by cTMS of the ulnar nerve at the elbow.
  
  
  RESULTS
  The S-D time constant with PA was shorter than for AP stimulation (230.9 ± 97.2 vs. 294.2 ± 90.9 μs; p<0.001). These values were similar to those calculated after stimulation of ulnar nerve (197 ± 47 μs). MEP latencies to AP, but not PA stimulation were affected by pulse width, showing longer latencies following short duration stimuli.
  
  
  CONCLUSIONS
  PA and AP stimuli appear to activate the axons of neurons with different time constants. Short duration AP pulses are more selective than longer pulses in recruiting longer latency corticospinal output.
  
  
  CONCLUSIONS
  More selective stimulation of neural elements may be achieved by manipulating pulse width and orientation.
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, London, UK; MoVeRe Group, Cyclotron Research Centre, University of Liege, Belgium.
authors.forename: Kevin
authors.initials: K
authors.lastname: D'Ostilio
authors.affiliation: Department of Psychiatry and Behavioral Sciences, Duke University, Durham, NC, USA; Technical University Munich, Munich, Germany.
authors.forename: Stefan M
authors.initials: SM
authors.lastname: Goetz
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, London, UK.
authors.forename: Ricci
authors.initials: R
authors.lastname: Hannah
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, London, UK; Department of Neurological Science, University of Milan, Milan, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Ciocca
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, London, UK; Department of Neurology, Scientific Institute Hospital San Raffaele, Milan, Italy.
authors.forename: Raffaella
authors.initials: R
authors.lastname: Chieffo
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, London, UK; Neuroscience Laboratory, Department of Neurology, China Medical University Hospital, Taichung, Taiwan; School of Medicine, China Medical University, Taichung, Taiwan.
authors.forename: Jui-Cheng A
authors.initials: JA
authors.lastname: Chen
authors.affiliation: Department of Psychiatry and Behavioral Sciences, Duke University, Durham, NC, USA; Department of Biomedical Engineering, Department of Electrical and Computer Engineering, Duke University, Durham, NC, USA.
authors.forename: Angel V
authors.initials: AV
authors.lastname: Peterchev
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, London, UK.
authors.forename: John C
authors.initials: JC
authors.lastname: Rothwell
mesh_terms: D000328:Adult; D058256:Brain Waves / Q000502:physiology*; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology*; D013997:Time Factors; D050781:Transcranial Magnetic Stimulation / Q000295:instrumentation / Q000379:methods*; D055815:Young Adult
keywords: Current direction; Input–output curve; Motor threshold; Pulse width; Strength–duration time constant; Transcranial magnetic stimulation