title: Cortical hemoglobin concentration changes underneath the coil after single-pulse transcranial magnetic stimulation: a near-infrared spectroscopy study.
abstract: Using near-infrared spectroscopy (NIRS) and multichannel probes, we studied hemoglobin (Hb) concentration changes when single-pulse transcranial magnetic stimulation (TMS) was applied over the left hemisphere primary motor cortex (M1). Seventeen measurement probes were centered over left M1. Subjects were studied in both active and relaxed conditions, with TMS intensity set at 100%, 120%, and 140% of the active motor threshold. The magnetic coils were placed so as to induce anteromedially directed currents in the brain. Hb concentration changes were more prominent at channels over M1 and posterior to it. Importantly, Hb concentration changes at M1 after TMS differed depending on whether the target muscle was in an active or relaxed condition. In the relaxed condition, Hb concentration increased up to 3-6 s after TMS, peaking at ∼6 s, and returned to the baseline. In the active condition, a smaller increase in Hb concentrations continued up to 3-6 s after TMS (early activation), followed by a decrease in Hb concentration from 9 to 12 s after TMS (delayed deactivation). Hb concentration changes in the active condition at higher stimulus intensities were more pronounced at locations posterior to M1 than at M1. We conclude that early activation occurs when M1 is activated transsynaptically. The relatively late deactivation may result from the prolonged inhibition of the cerebral cortex after activation. The posterior-dominant activation at higher intensities in the active condition may result from an additional activation of the sensory cortex due to afferent inputs from muscle contraction evoked by the TMS.
authors.affiliation: Department of Rehabilitation, Faculty of Medical Science and Welfare, Tohoku Bunka Gakuen University, Sendai, Japan. furubayashi-tky@umin.ac.jp
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Furubayashi
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Mochizuki
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Terao
authors.forename: Noritoshi
authors.initials: N
authors.lastname: Arai
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Hanajima
authors.forename: Masashi
authors.initials: M
authors.lastname: Hamada
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Matsumoto
authors.forename: Setsu
authors.initials: S
authors.lastname: Nakatani-Enomoto
authors.forename: Shingo
authors.initials: S
authors.lastname: Okabe
authors.forename: Akihiro
authors.initials: A
authors.lastname: Yugeta
authors.forename: Satomi
authors.initials: S
authors.lastname: Inomata-Terada
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Ugawa
mesh_terms: D000328:Adult; D005260:Female; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009044:Motor Cortex / Q000737:chemistry*; D019265:Spectroscopy, Near-Infrared; D050781:Transcranial Magnetic Stimulation
chemical_list: D006454:Hemoglobins