title: Input-Output Characteristics of Late Corticospinal Silent Period Induced by Transcranial Magnetic Stimulation.
abstract: OBJECTIVE
  Corticospinal silent period (SP) may be interrupted by a burst of muscle activity followed by a second (late) SP, generally assumed to be a continuation from the primary SP. Our objective was to characterize the input-output behavior of the late SP.
  
  
  METHODS
  Transcranial magnetic stimulation was applied on the cortical representation area of the right-hand muscles of 12 healthy subjects. Single-pulse transcranial magnetic stimulation was given with varying stimulation intensities normalized to the individual resting motor threshold (60% to 130% of the resting motor threshold) during voluntary muscle contraction. Electromyogram was recorded from first dorsal interosseous and abductor pollicis brevis muscles. Primary and late SPs were analyzed as absolute SPs, and input-output characteristics were assessed.
  
  
  RESULTS
  The late SP exhibited fundamentally different input-output characteristics from that of the primary SP. The late SP most likely presented itself at stimulation intensities of 90% to 100% of the resting motor threshold.
  
  
  CONCLUSIONS
  Different input-output characteristics of the late SP compared with the primary SP indicate that the late SP possess mechanisms different from the primary SP. The exact origin of the late SP remains unclear. Understanding the origins of the late SP could provide valuable insight on corticospinal inhibitory processes.
authors.affiliation: *Department of Clinical Neurophysiology, Kuopio University Hospital, Kuopio, Finland; †Department of Applied Physics, University of Eastern Finland, Kuopio, Finland; ‡Institute of Clinical Medicine, University of Eastern Finland, Kuopio, Finland; §Department of Neuroscience and Biomedical Engineering, Aalto University School of Science, Espoo, Finland; ‖Department of Clinical Radiology, Kuopio University Hospital, Kuopio, Finland; and ¶Department of Physiology, University of Eastern Finland, Kuopio, Finland Nexstim Plc, Helsinki, Finland.
authors.forename: Elisa
authors.initials: E
authors.lastname: Kallioniemi
authors.forename: Laura
authors.initials: L
authors.lastname: Säisänen
authors.forename: Minna
authors.initials: M
authors.lastname: Pitkänen
authors.forename: Mervi
authors.initials: M
authors.lastname: Könönen
authors.forename: Jari
authors.initials: J
authors.lastname: Karhu
authors.forename: Petro
authors.initials: P
authors.lastname: Julkunen
mesh_terms: D000328:Adult; D001703:Biophysics; D002540:Cerebral Cortex / Q000502:physiology*; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000294:innervation; D011712:Pyramidal Tracts / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology*; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult