Focal Hemodynamic Responses in the Stimulated Hemisphere During High-Definition Transcranial Direct Current Stimulation

Neuromodulation. 2018 Jun;21(4):348-354. doi: 10.1111/ner.12632. Epub 2017 Jul 17.

Abstract

Objective: High-definition transcranial direct current stimulation (HD-tDCS) using a 4 × 1 electrode montage has been previously shown using modeling and physiological studies to constrain the electric field within the spatial extent of the electrodes. The aim of this proof-of-concept study was to determine if functional near-infrared spectroscopy (fNIRS) neuroimaging can be used to determine a hemodynamic correlate of this 4 × 1 HD-tDCS electric field on the brain.

Materials and methods: In a three session cross-over study design, 13 healthy males received one sham (2 mA, 30 sec) and two real (HD-tDCS-1 and HD-tDCS-2, 2 mA, 10 min) anodal HD-tDCS targeting the left M1 via a 4 × 1 electrode montage (anode on C3 and 4 return electrodes 3.5 cm from anode). The two real HD-tDCS sessions afforded a within-subject replication of the findings. fNIRS was used to measure changes in brain hemodynamics (oxygenated hemoglobin integral-O2 Hbint ) during each 10 min session from two regions of interest (ROIs) in the stimulated left hemisphere that corresponded to "within" (Lin ) and "outside" (Lout ) the spatial extent of the 4 × 1 electrode montage, and two corresponding ROIs (Rin and Rout ) in the right hemisphere.

Results: The ANOVA showed that both real anodal HD-tDCS compared to sham induced a significantly greater O2 Hbint in the Lin than Lout ROIs of the stimulated left hemisphere; while there were no significant differences between the real and sham sessions for the right hemisphere ROIs. Intra-class correlation coefficients showed "fair-to-good" reproducibility for the left stimulated hemisphere ROIs.

Conclusions: The greater O2 Hbint "within" than "outside" the spatial extent of the 4 × 1 electrode montage represents a hemodynamic correlate of the electrical field distribution, and thus provides a prospective reliable method to determine the dose of stimulation that is necessary to optimize HD-tDCS parameters in various applications.

Keywords: Blood flow; electric field; fNIRS; motor cortex stimulation; tDCS.

MeSH terms

  • Adult
  • Biophysics
  • Brain / metabolism
  • Brain / physiology*
  • Brain Mapping*
  • Cross-Over Studies
  • Electrodes
  • Functional Laterality / physiology*
  • Hemodynamics / physiology*
  • Humans
  • Male
  • Middle Aged
  • Oxyhemoglobins / metabolism
  • Random Allocation
  • Spectroscopy, Near-Infrared
  • Transcranial Direct Current Stimulation / methods*
  • Young Adult

Substances

  • Oxyhemoglobins