Is motor learning mediated by tDCS intensity?

1. Is motor learning mediated by tDCS intensity? J. F. Daphnie Leenus1,2, Koen Cuypers1-3, Femke E. van den Berg3, Michael A. Nitsche4, Herbert Thijs5,Nicole Wenderoth 3,6, Raf Meesen1-3 • 1 BIOMED, Hasselt University, Diepenbeek, Belgium • 2 REVAL, PHL University college, Diepenbeek, Belgium • 3 Motor Control Laboratory, Research Center for Movement Control and Neuroplasticity, K.U. Leuven, Leuven, Belgium • 4 Georg-August University, Department of Clinical Neurophysiology, Göttiingen, Germany • 5 CENSTAT, Hasselt University, Diepenbeek, Belgium • 6 Neural Control of movement lab, Department of Health Sciences and Technology, ETH Zurich, Switzerland • Introduction • Previous research demonstrated that a single session of anodal tDCS over the primary motor cortex (M1) was able to ameliorates motor learning • Numerous different parameter settings are used in tDCS studies (electrode size and placement, stimulation intensity etc..) • This study was conducted to unveal the correlation between current intensity and motor learning in healthy subjects • Discussion • Healthy subjects were able to learn the sequence task and the motor learning improved with the stimulation • The motor learning increased with the increase in the stimulation intensity • A remarkable long-term effect of tDCS was observed during the post-intervention (30min after the stimulation) • Previous studies has explained about the ability of single session tDCS in cortical excitability. This is the first study explaining the intensity-dependent motor learning effects of tDCS • In contrast with other studies conducted in healthy subjects, we found no significant differences at 1mA stimulation and sham condition • We suggest that increasing the sample size and the current intensity (for example: 2mA) might lead to increased effects between conditions tDCS stimulation • Complete as many correct sequences as fast as possible • 1 block = 30 sec performance + 30 sec rest • PRE (3 blocks) – TRAINING (26 blocks) – POST (3 blocks) • The sequences were [4 2 1 3 4 2 3 2] and [2 4 3 1 2 3 2 4] (1 = index finger, 2 = middle finger, 3 = ring finger and 4 = little finger) • No feedback was provided • Compound measurement of performance = % correct sequences/mean intertab interval (ITI) • Experimental design • Double-blind cross-over design • Interval between sessions: 1 week • 2 sessions: tDCS or SHAM-tDCS applied during the motor training • Stimulation parameters: • Duration: 20 min • Constant current • Intensities: 1mA ,1.5mA • Sham: Received current for first 26sec • Electrode size: • Anode: 25cm2,current density • 0.04mA/cm2 for 1mA • 0.06mA/cm2 for 1.5mA • Cathode: 50cm2, current density • 0.02mA/cm2 for 1mA • 0.03mA/cm2 for 1.5mA tDCS • Stimulation location: • Anode: Hotspot FDI • Cathode: contralateral supraorbital region • Results • The percentage of correct sequences/mean ITI improved in both sham and stimulation conditions (p < .0001) • During motor learning, a significant INTENSITY X TIME interaction was reported • Slope analysis: the slope was significantly steeper at 1.5mA. Indicating, an increased motor performance rate as compared to 1mA and SHAM • At post-intervention (30 min later), a paired t-test revealed a significant improvement in motor performance at 1.5mA compared with Sham condition • Materials and methods • Subjects • 13 Healthy subjects (7M: 6F, mean age 19.92 +/- 1.12 years) were included • 11 subjects were right-handed and 2 were left-handed • References • Hummel,F. et al. (2005) Effects of non-invasive cortical stimulation on skilled motor function in chronic stroke. Brain 128, 490-499 • Fregni,F. et al. (2006) Noninvasive cortical stimulation with transcranial direct current stimulation in Parkinson's disease. Mov Disord. 21, 1693-1702 • Nitsche,M.A. et al. (2005) Modulating parameters of excitability during and after transcranial direct current stimulation of the human motor cortex. J. Physiol 568, 291-303 Study design Motor training: Sequence task • TMS Hotspot finding • Stimulation was applied on the hotspot of FDI muscle for each subject as determined by TMS Correspondence Please contact : Prof.Dr.Raf Meesen raf.meesen@uhasselt.be J. F .Daphnie Leenus, Dra daphnie.leenus@uhasselt.be