Original ArticleDaily transcranial direct current stimulation (tDCS) leads to greater increases in cortical excitability than second daily transcranial direct current stimulation
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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This project was supported by Australian National Health and Medical Research Council Project Grant no. 510142.