Current intensity- and polarity-specific online and aftereffects of transcranial direct current stimulation: An fMRI study

Hum Brain Mapp. 2020 Apr 15;41(6):1644-1666. doi: 10.1002/hbm.24901. Epub 2019 Dec 20.

Abstract

Transcranial direct current stimulation (tDCS) induces polarity- and dose-dependent neuroplastic aftereffects on cortical excitability and cortical activity, as demonstrated by transcranial magnetic stimulation (TMS) and functional imaging (fMRI) studies. However, lacking systematic comparative studies between stimulation-induced changes in cortical excitability obtained from TMS, and cortical neurovascular activity obtained from fMRI, prevent the extrapolation of respective physiological and mechanistic bases. We investigated polarity- and intensity-dependent effects of tDCS on cerebral blood flow (CBF) using resting-state arterial spin labeling (ASL-MRI), and compared the respective changes to TMS-induced cortical excitability (amplitudes of motor evoked potentials, MEP) in separate sessions within the same subjects (n = 29). Fifteen minutes of sham, 0.5, 1.0, 1.5, and 2.0-mA anodal or cathodal tDCS was applied over the left primary motor cortex (M1) in a randomized repeated-measure design. Time-course changes were measured before, during and intermittently up to 120-min after stimulation. ROI analyses indicated linear intensity- and polarity-dependent tDCS after-effects: all anodal-M1 intensities increased CBF under the M1 electrode, with 2.0-mA increasing CBF the greatest (15.3%) compared to sham, while all cathodal-M1 intensities decreased left M1 CBF from baseline, with 2.0-mA decreasing the greatest (-9.3%) from sham after 120-min. The spatial distribution of perfusion changes correlated with the predicted electric field, as simulated with finite element modeling. Moreover, tDCS-induced excitability changes correlated more strongly with perfusion changes in the left sensorimotor region compared to the targeted hand-knob region. Our findings reveal lasting tDCS-induced alterations in cerebral perfusion, which are dose-dependent with tDCS parameters, but only partially account for excitability changes.

Keywords: arterial spin labeling; cerebral blood flow; current intensity; inter-individual variability; motor cortex; transcranial direct current stimulation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Brain Mapping
  • Cerebral Cortex / diagnostic imaging
  • Cerebral Cortex / physiology
  • Cerebrovascular Circulation
  • Electrodes
  • Electromagnetic Fields
  • Evoked Potentials, Motor
  • Female
  • Humans
  • Magnetic Resonance Imaging / methods*
  • Male
  • Motor Cortex / diagnostic imaging
  • Motor Cortex / physiology
  • Neuronal Plasticity / physiology
  • Online Systems
  • Somatosensory Cortex / diagnostic imaging
  • Somatosensory Cortex / physiology
  • Spin Labels
  • Transcranial Direct Current Stimulation*
  • Young Adult

Substances

  • Spin Labels