Elsevier

Brain Stimulation

Volume 5, Issue 3, July 2012, Pages 208-213
Brain Stimulation

Original Article
Daily transcranial direct current stimulation (tDCS) leads to greater increases in cortical excitability than second daily transcranial direct current stimulation

https://doi.org/10.1016/j.brs.2011.04.006Get rights and content

Background

Evidence from recent clinical trials suggests that transcranial direct current stimulation (tDCS) may have potential in treating neuropsychiatric disorders. However, the optimal frequency at which tDCS sessions should be administered is unknown.

Objective/Hypothesis

This study investigated the effects of daily or second daily tDCS sessions on motor cortical excitability, over a 5-day period.

Methods

Twelve healthy volunteers received daily or second daily sessions of tDCS to the left primary motor cortex over the study period, in a randomized, intraindividual crossover design. Motor cortical excitability was assessed before and after tDCS at each session through responses to transcranial magnetic stimulation.

Results

Over a fixed 5-day period, tDCS induced greater increases in MEP amplitude when given daily rather than second daily. Analyses showed that this difference reflected greater cumulative effects between sessions rather than a greater response to each individual tDCS session.

Conclusions

These results demonstrate that in the motor cortex of healthy volunteers, tDCS alters cortical excitability more effectively when given daily rather than second daily over a 5-day period.

Section snippets

Participants

Twelve healthy, right-handed males (mean age 21.4 years; range 20-27) participated in the experiment, which was approved by the human research ethics committee of the University of New South Wales. For expedience, females were excluded from the study due to effects of menstrual variation on cortical excitability being a potential confound in women of reproductive age.18, 19 Subjects were not on any medications and had no history of acute or chronic medical, neurologic, or psychiatric disease.

Results

The TMS intensity required to elicit 1 mV responses was 52.9 ± 9.9% (expressed as percentage of maximum machine power) in the daily condition and 51.8 ± 8.8% in the second daily condition; there was no significant difference (t = 1.13, P = 0.28). Resting motor thresholds at the start of each week, 43.5 ± 7.7 for the daily condition and 43.6 ± 7.1 for second daily were also not significantly different (t = −0.09, P = 0.93).

The three-factor ANCOVA found a significant main effect of tDCS frequency

Discussion

Extending findings from previous studies,2, 3, 17 which showed that single sessions of anodal tDCS given at 1 mA for 5 to 13 minutes induced increases in motor cortical excitability that lasted for minutes to hours poststimulation, the current study found that tDCS given continuously at 2 mA for 20 minutes also induced changes in excitability that lasted for at least 2 hours, with further cumulative increases in excitability when sessions were repeated on a daily basis over a 5-day period.

Acknowledgments

We gratefully acknowledge the help of Manasi Kogekar in formatting the manuscript for submission.

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  • Cited by (0)

    This project was supported by Australian National Health and Medical Research Council Project Grant no. 510142.

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