Experimental Brain Research

, Volume 234, Issue 9, pp 2629–2642 | Cite as

Effects of a common transcranial direct current stimulation (tDCS) protocol on motor evoked potentials found to be highly variable within individuals over 9 testing sessions

  • Jared Cooney HorvathEmail author
  • Simon J. Vogrin
  • Olivia Carter
  • Mark J. Cook
  • Jason D. Forte
Research Article


Transcranial direct current stimulation (tDCS) uses a weak electric current to modulate neuronal activity. A neurophysiologic outcome measure to demonstrate reliable tDCS modulation at the group level is transcranial magnetic stimulation engendered motor evoked potentials (MEPs). Here, we conduct a study testing the reliability of individual MEP response patterns following a common tDCS protocol. Fourteen participants (7m/7f) each underwent nine randomized sessions of 1 mA, 10 min tDCS (3 anode; 3 cathode; 3 sham) delivered using an M1/orbito-frontal electrode montage (sessions separated by an average of ~5.5 days). Fifteen MEPs were obtained prior to, immediately following and in 5 min intervals for 30 min following tDCS. TMS was delivered at 130 % resting motor threshold using neuronavigation to ensure consistent coil localization. A number of non-experimental variables were collected during each session. At the individual level, considerable variability was seen among different testing sessions. No participant demonstrated an excitatory response ≥20 % to all three anodal sessions, and no participant demonstrated an inhibitory response ≥20 % to all three cathodal sessions. Intra-class correlation revealed poor anodal and cathodal test–retest reliability [anode: ICC(2,1) = 0.062; cathode: ICC(2,1) = 0.055] and moderate sham test–retest reliability [ICC(2,1) = 0.433]. Results also revealed no significant effect of tDCS at the group level. Using this common protocol, we found the effects of tDCS on MEP amplitudes to be highly variable at the individual level. In addition, no significant effects of tDCS on MEP amplitude were found at the group level. Future studies should consider utilizing a more strict experimental protocol to potentially account for intra-individual response variations.


Transcranial direct current stimulation (tDCS) Transcranial magnetic stimulation (TMS) Motor evoked potentials (MEPs) Longitudinal Reliability 



ARC-SRI: Science of Learning Research Centre (Project Number SR120300015).

Supplementary material

221_2016_4667_MOESM1_ESM.docx (17 kb)
Supplementary material 1 (DOCX 17 kb)


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Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  • Jared Cooney Horvath
    • 1
    • 2
    • 3
    Email author
  • Simon J. Vogrin
    • 2
  • Olivia Carter
    • 1
  • Mark J. Cook
    • 1
    • 2
  • Jason D. Forte
    • 1
  1. 1.Melbourne School of Psychological SciencesUniversity of MelbourneMelbourneAustralia
  2. 2.Departments of Medicine and Neurology, St. Vincent’s HospitalUniversity of MelbourneMelbourneAustralia
  3. 3.Melbourne Graduate School of EducationUniversity of MelbourneMelbourneAustralia

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