title: Transcranial laser stimulation improves human cerebral oxygenation.
abstract: OBJECTIVE
  Transcranial laser stimulation of the brain with near-infrared light is a novel form of non-invasive photobiomodulation or low-level laser therapy (LLLT) that has shown therapeutic potential in a variety of neurological and psychological conditions. Understanding of its neurophysiological effects is essential for mechanistic study and treatment evaluation. This study investigated how transcranial laser stimulation influences cerebral hemodynamics and oxygenation in the human brain in vivo using functional near-infrared spectroscopy (fNIRS).
  
  
  METHODS
  Two separate experiments were conducted in which 1,064-nm laser stimulation was administered at (1) the center and (2) the right side of the forehead, respectively. The laser emitted at a power of 3.4 W and in an area of 13.6 cm2, corresponding to 0.25 W/cm2 irradiance. Stimulation duration was 10 minutes. Nine healthy male and female human participants of any ethnic background, in an age range of 18-40 years old were included in each experiment.
  
  
  RESULTS
  In both experiments, transcranial laser stimulation induced an increase of oxygenated hemoglobin concentration (Δ[HbO2 ]) and a decrease of deoxygenated hemoglobin concentration (Δ[Hb]) in both cerebral hemispheres. Improvements in cerebral oxygenation were indicated by a significant increase of differential hemoglobin concentration (Δ[HbD] = Δ[HbO2 ] - Δ[Hb]). These effects increased in a dose-dependent manner over time during laser stimulation (10 minutes) and persisted after laser stimulation (6 minutes). The total hemoglobin concentration (Δ[HbT] = Δ[HbO2] + Δ[Hb]) remained nearly unchanged in most cases.
  
  
  CONCLUSIONS
  Near-infrared laser stimulation applied to the forehead can transcranially improve cerebral oxygenation in healthy humans.
authors.affiliation: Department of Bioengineering, University of Texas, Arlington, Texas, 76010.
authors.forename: Fenghua
authors.initials: F
authors.lastname: Tian
authors.affiliation: Department of Bioengineering, University of Texas, Arlington, Texas, 76010.
authors.forename: Snehal N
authors.initials: SN
authors.lastname: Hase
authors.affiliation: Department of Psychology and Institute for Neuroscience, University of Texas, Austin, Texas, 78712.
authors.forename: F
authors.initials: F
authors.lastname: Gonzalez-Lima
authors.affiliation: Department of Bioengineering, University of Texas, Arlington, Texas, 76010.
authors.forename: Hanli
authors.initials: H
authors.lastname: Liu
mesh_terms: D000293:Adolescent; D000328:Adult; D015415:Biomarkers / Q000378:metabolism; D001921:Brain / Q000378:metabolism / Q000528:radiation effects*; D005260:Female; D064368:Healthy Volunteers; D006439:Hemodynamics / Q000528:radiation effects*; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D028022:Low-Level Light Therapy / Q000379:methods*; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D019265:Spectroscopy, Near-Infrared / Q000379:methods; D055815:Young Adult
chemical_list: D015415:Biomarkers; D006454:Hemoglobins; D010100:Oxygen
keywords: brain tissue oxygenation; functional near-infrared spectroscopy (fNIRS); low-level laser therapy (LLLT); photobiomodulation
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