title: Quadri-pulse stimulation induces stimulation frequency dependent cortical hemoglobin concentration changes within the ipsilateral motor cortical network.
abstract: BACKGROUND
  Imaging studies investigating repetitive transcranial magnetic stimulation (rTMS) mediated hemodynamic consequences revealed inconsistent results, mainly due to differences in rTMS parameters and technical difficulties with simultaneous recordings during rTMS.
  
  
  OBJECTIVE
  Quadri-pulse rTMS (QPS) induces bidirectional long-term plasticity of the human primary motor cortex (M1). To evaluate its on-line effects, near infrared spectroscopy (NIRS) recordings were performed during QPS. We hypothesized that on-line effects during QPS are different from long-term aftereffects.
  
  
  METHODS
  Using a novel TMS - on-line multi-channel NIRS setup we recorded hemoglobin concentration [Hb] changes at the stimulated M1 and adjacent sensory-motor areas during QPS protocols inducing oppositely directed aftereffects (QPS-5: interstimulus interval (ISI) 5 ms, potentiation; QPS-50: ISI 50 ms, depression). In two experiments we studied NIRS changes during either single or repeated QPS bursts.
  
  
  RESULTS
  The repetitive QPS-5 bursts significantly decreased oxyhemoglobin concentration ([oxy-Hb]) in the ipsilateral M1. A single QPS-5 burst decreased [oxy-Hb] in the M1 and premotor cortex. QPS-50 induced no significant NIRS changes at any sites.
  
  
  CONCLUSIONS
  QPS can significantly alter cortical hemodynamics depending on the stimulation frequency. While bidirectional long-term aftereffects of QPS reflect synaptic efficacy changes, unidirectional on-line effects during QPS may represent pure electrophysiological property changes within the cell membrane or synapse. Since neuronal postexcitatory inhibitory postsynaptic potentials typically peak within the first 10-20 ms, only pulses delivered at higher frequencies may lead to summation of the inhibitory effects, resulting in [oxy-Hb] decrease only after QPS-5. Our new TMS-NIRS setup may be valuable to investigate TMS induced neurovascular coupling mechanisms in humans.
authors.affiliation: Department of Neurology, School of Medicine, Fukushima Medical University, 1 Hikarigaoka, 960-1295 Fukushima, Japan. groiss-js@umin.net
authors.forename: Stefan Jun
authors.initials: SJ
authors.lastname: Groiss
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Mochizuki
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Furubayashi
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Kobayashi
authors.forename: Setsu
authors.initials: S
authors.lastname: Nakatani-Enomoto
authors.forename: Koichiro
authors.initials: K
authors.lastname: Nakamura
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Ugawa
mesh_terms: D000328:Adult; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology*; D006454:Hemoglobins / Q000032:analysis / Q000378:metabolism*; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000098:blood supply*; D019265:Spectroscopy, Near-Infrared; D050781:Transcranial Magnetic Stimulation / Q000379:methods*
chemical_list: D006454:Hemoglobins