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 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 / 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 [ ] and [ ] (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, Fregni,F. et al. (2006) Noninvasive cortical stimulation with transcranial direct current stimulation in Parkinson's disease. Mov Disord. 21, 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, Correspondence Please contact : Prof.Dr.Raf Meesen J. F.Daphnie Leenus, Dra