Intra-Subject Consistency and Reliability of Response Following 2 mA Transcranial Direct Current Stimulation

Katherine Dyke; Soyoung Kim; Georgina M Jackson; Stephen R Jackson

doi:10.1016/j.brs.2016.06.052

Intra-Subject Consistency and Reliability of Response Following 2 mA Transcranial Direct Current Stimulation

Brain Stimul. 2016 Nov-Dec;9(6):819-825. doi: 10.1016/j.brs.2016.06.052. Epub 2016 Jun 21.

Authors

Katherine Dyke¹, Soyoung Kim¹, Georgina M Jackson², Stephen R Jackson³

Affiliations

¹ School of Psychology, University of Nottingham, Nottingham NG7 2RD, UK.
² School of Medicine, Division of Psychiatry, Institute of Mental Health, University of Nottingham, Nottingham NG7 2TU, UK.
³ School of Psychology, University of Nottingham, Nottingham NG7 2RD, UK. Electronic address: Stephen.jackson@nottingham.ac.uk.

PMID: 27387569
DOI: 10.1016/j.brs.2016.06.052

Abstract

Background: Transcranial direct current stimulation (tDCS) is a popular non-invasive brain stimulation technique that has been shown to influence cortical excitability. While polarity specific effects have often been reported, this is not always the case, and variability in both the magnitude and direction of the effects have been observed.

Objective/hypothesis: We aimed to explore the consistency and reliability of the effects of tDCS by investigating changes in cortical excitability across multiple testing sessions in the same individuals. A within subjects design was used to investigate the effects of anodal and cathodal tDCS applied to the motor cortex. Four experimental sessions were tested for each polarity in addition to two sham sessions.

Methods: Transcranial magnetic stimulation (TMS) was used to measure cortical excitability (TMS recruitment curves). Changes in excitability were measured by comparing baseline measures and those taken immediately following 20 minutes of 2 mA stimulation or sham stimulation.

Results: Anodal tDCS significantly increased cortical excitability at a group level, whereas cathodal tDCS failed to have any significant effects. The sham condition also failed to show any significant changes. Analysis of intra-subject responses to anodal stimulation across four sessions suggest that the amount of change in excitability across sessions was only weakly associated, and was found to have poor reliability across sessions (ICC = 0.276). The effects of cathodal stimulation show even poorer reliability across sessions (ICC = 0.137). In contrast ICC analysis for the two sessions of sham stimulation reflect a moderate level of reliability (ICC = .424).

Conclusions: Our findings indicate that although 2 mA anodal tDCS is effective at increasing cortical excitability at group level, the effects are unreliable across repeated testing sessions within individual participants. Our results suggest that 2 mA cathodal tDCS does not significantly alter cortical excitability immediately following stimulation and that there is poor reliability of the effect within the same individual across different testing sessions.

Keywords: Cortical excitability; Motor cortex; Transcranial direct current stimulation (tDCS); Transcranial magnetic stimulation (TMS).

MeSH terms

Adult
Cortical Excitability / physiology*
Evoked Potentials, Motor / physiology
Female
Humans
Male
Motor Cortex / physiology*
Reproducibility of Results
Transcranial Direct Current Stimulation / methods*
Transcranial Magnetic Stimulation / methods*
Young Adult