title: The use of F-response in defining interstimulus intervals appropriate for LTP-like plasticity induction in lower limb spinal paired associative stimulation.
abstract: BACKGROUND
  In spinal paired associative stimulation (PAS), orthodromic volleys are induced by transcranial magnetic stimulation (TMS) in upper motor neurons, and antidromic volleys by peripheral nerve stimulation (PNS) in lower motor neurons of human corticospinal tract. The volleys arriving synchronously to the corticomotoneuronal synapses induce spike time-dependent plasticity in the spinal cord. For clinical use of spinal PAS, it is important to develop protocols that reliably induce facilitation of corticospinal transmission. Due to variability in conductivity of neuronal tracts in neurological patients, it is beneficial to estimate interstimulus interval (ISI) between TMS and PNS on individual basis. Spinal root magnetic stimulation has previously been used for this purpose in spinal PAS targeting upper limbs. However, at lumbar level this method does not take into account the conduction time of spinal nerves of the cauda equina in the spinal canal.
  
  
  METHODS
  For lower limbs spinal PAS, we propose estimating appropriate ISIs on the basis of F-response and motor-evoked potential (MEP) latencies. The use of navigation in TMS and ensuring correct PNS electrode placement with F-response recording enhances the precision of the method.
  
  
  RESULTS
  Our protocol induced 186±17% (mean±STE) MEP amplitude facilitation in healthy subjects, being effective in all subjects and nerves tested.
  
  
  CONCLUSIONS
  We report for the first time the individual estimation of ISIs in spinal PAS for lower limbs.
  
  
  CONCLUSIONS
  Estimation of ISI on the basis of F and MEP latencies is sufficient to effectively enhance corticospinal transmission by lower limb spinal PAS in healthy subjects.
authors.affiliation: Clinical Neurosciences, Neurology, University of Helsinki and Helsinki University Hospital, P.O. Box 372, FI-00029 Helsinki, Finland; BioMag Laboratory, HUS Medical Imaging Center, University of Helsinki and Helsinki University Hospital, P.O. Box 340, FI-00029 Helsinki, Finland. Electronic address: anastasia.shulga@helsinki.fi.
authors.forename: Anastasia
authors.initials: A
authors.lastname: Shulga
authors.affiliation: BioMag Laboratory, HUS Medical Imaging Center, University of Helsinki and Helsinki University Hospital, P.O. Box 340, FI-00029 Helsinki, Finland; Neuroscience Center, University of Helsinki, P.O. Box 56, FI-00014, Finland. Electronic address: pantelis.lioumis@hus.fi.
authors.forename: Pantelis
authors.initials: P
authors.lastname: Lioumis
authors.affiliation: Clinical Neurosciences, Clinical Neurophysiology, HUS Medical Imaging Center, University of Helsinki and Helsinki University Hospital, P.O. Box 340, FI-00029 Helsinki, Finland. Electronic address: erika.kirveskari@hus.fi.
authors.forename: Erika
authors.initials: E
authors.lastname: Kirveskari
authors.affiliation: Validia Rehabilitation Center, P.O. Box 103, FI-00251 Helsinki, Finland. Electronic address: sarianna.savolainen@thl.fi.
authors.forename: Sarianna
authors.initials: S
authors.lastname: Savolainen
authors.affiliation: BioMag Laboratory, HUS Medical Imaging Center, University of Helsinki and Helsinki University Hospital, P.O. Box 340, FI-00029 Helsinki, Finland. Electronic address: jyrki.makela@hus.fi.
authors.forename: Jyrki P
authors.initials: JP
authors.lastname: Mäkelä
authors.affiliation: Clinical Neurosciences, Neurology, University of Helsinki and Helsinki University Hospital, P.O. Box 372, FI-00029 Helsinki, Finland. Electronic address: aarne.ylinen@hus.fi.
authors.forename: Aarne
authors.initials: A
authors.lastname: Ylinen
mesh_terms: D000328:Adult; D004599:Electric Stimulation Therapy / Q000379:methods*; D019054:Evoked Potentials, Motor; D005240:Feasibility Studies; D005260:Female; D005267:Femoral Nerve / Q000502:physiology; D006801:Humans; D035002:Lower Extremity / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D009473:Neuronal Plasticity / Q000502:physiology*; D010543:Peroneal Nerve / Q000502:physiology; D011712:Pyramidal Tracts / Q000502:physiology*; D013979:Tibial Nerve / Q000502:physiology; D050781:Transcranial Magnetic Stimulation / Q000379:methods*
keywords: Electrical stimulation therapy; F-response; Neuronal plasticity; Paired associative stimulation; Transcranial magnetic stimulation