title: Transcranial application of near-infrared low-level laser can modulate cortical excitability.
abstract: OBJECTIVE
  Near-infrared low-level laser (NIR-LLL) irradiation penetrates scalp and skull and can reach superficial layers of the cerebral cortex. It was shown to improve the outcome of acute stroke in both animal and human studies. In this study we evaluated whether transcranial laser stimulation (TLS) with NIR-LLL can modulate the excitability of the motor cortex (M1) as measured by transcranial magnetic stimulation (TMS).
  
  
  METHODS
  TLS was applied for 5 minutes over the representation of the right first dorsal interosseal muscle (FDI) in left primary motor cortex (M1), in 14 healthy subjects. Motor evoked potentials (MEPs) from the FDI, elicited by single-pulse TMS, were measured at baseline and up to 30 minutes after the TLS.
  
  
  RESULTS
  The average MEP size was significantly reduced during the first 20 minutes following the TLS. The pattern was present in 10 (71.5%) of the participants. The MEP size reduction correlated negatively with the motor threshold at rest.
  
  
  CONCLUSIONS
  TLS with NIR-LLL induced transitory reduction of the excitability of the stimulated cortex. These findings give further insights into the mechanisms of TLS effects in the human cerebral cortex, paving the way for potential applications of TLS in treatment of stroke and in other clinical settings.
authors.affiliation: Department of Rehabilitation, Faculty of Medicine, University of Belgrade, 11000, Belgrade, Serbia; Klinika za Rehabilitaciju "Dr Miroslav Zotović", 11000, Belgrade, Serbia.
authors.forename: Ljubica M
authors.initials: LM
authors.lastname: Konstantinović
authors.forename: Milan B
authors.initials: MB
authors.lastname: Jelić
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Jeremić
authors.forename: Vuk B
authors.initials: VB
authors.lastname: Stevanović
authors.forename: Sladjan D
authors.initials: SD
authors.lastname: Milanović
authors.forename: Saša R
authors.initials: SR
authors.lastname: Filipović
mesh_terms: D000328:Adult; D019054:Evoked Potentials, Motor / Q000528:radiation effects*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D028022:Low-Level Light Therapy / Q000379:methods*; D008875:Middle Aged; D009044:Motor Cortex / Q000502:physiology / Q000528:radiation effects*; D050781:Transcranial Magnetic Stimulation
keywords: human; membrane potential; neuronal excitability; photobiomodulation; transcranial magnetic stimulation