1. Is motor learning mediated by tDCS intensity? J. F. Daphnie Leenus 1,2, Koen Cuypers 1-3, Femke E. van den Berg 3, Michael A. Nitsche 4, Herbert Thijs 5,Nicole Wenderoth 3,6, Raf Meesen 1-3 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, G öttiingen, 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 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 Study design TMS Hotspot finding  Stimulation was applied on the hotspot of FDI muscle for each subject as determined by TMS tDCS stimulation 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: 25cm 2,current density 0.04mA/cm 2 for 1mA 0.06mA/cm 2 for 1.5mA Cathode: 50cm 2, current density 0.02mA/cm 2 for 1mA 0.03mA/cm 2 for 1.5mA tDCS Stimulation location:  Anode: Hotspot FDI  Cathode: contralateral supraorbital region Motor training: Sequence task  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) 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 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 References 1. Hummel,F. et al. (2005) Effects of non-invasive cortical stimulation on skilled motor function in chronic stroke. Brain 128, 490-499 2. Fregni,F. et al. (2006) Noninvasive cortical stimulation with transcranial direct current stimulation in Parkinson's disease. Mov Disord. 21, 1693-1702 3. 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 Correspondence Please contact : Prof.Dr.Raf Meesen raf.meesen@uhasselt.be J. F.Daphnie Leenus, Dra daphnie.leenus@uhasselt.be