Objective: To further investigate the extent to which these phenomena are associated with response preparation we measured MEP amplitude and SICI during the foreperiod of a warned Go/NoGo task, in which the amount of response related information available in the warning signal was manipulated. Method: Three different warning signals were presented, one which indicated that a Go signal was imminent (83% valid), one which indicated that a NoGo signal was imminent (100% valid) and one which was uninformative about the nature of the imminent response signal. Results: MEP amplitude was suppressed (Experiment 1) and SICI reduced (Experiment 2) equally in all of the warned conditions relative to when TMS was delivered in the inter-trial interval, suggesting that the specific modu- lations of primary motor cortex (M1) excitability during the foreperiod do not depend on response-related information in the warning signal. Conclusion: The simultaneous reduction of MEP amplitude and SICI during the foreperiod suggests that a warning signal induces automatic motor cortical activation (Boulinguez et al. 2008) which is balanced by a competing inhibition to prevent premature response during the foreperiod (Davranche et al. 2007). TMS Poster Only 100 Intracortical excitability in healthy human subjects after tongue-training Baad-Hansen L 1 , Blicher J 2 , Lapitskaya N 2 , Nielsen JF 2 , Svensson P 1 , 1 University of Aarhus (Aarhus C, DK); 2 Hammel Neurocentre (Hammel, DK) Tongue dysfunction often has serious implications for a patient’s general and oral health. Training related short-term changes in corticomotor pathways and short-interval intracortical inhibitory (SICI) and facilitatory (ICF) networks evaluated by paired-pulse transcranial magnetic stimula- tion (ppTMS) have not been described in detail for tongue muscles. Objectives: This study examined short-term changes in ipsi- and contra- lateral single motor evoked potentials (MEPs), SICI, and ICF in tongue motor cortex after a standardized tongue-training task. Methods: Thirteen healthy volunteers (6 men, 7 women) were examined before and after 30 min of tongue-training. Single and ppTMS were applied to the hotspot for the tongue motor cortex and MEPs were recorded bilaterally from tongue muscles. The TMS protocol consisted of 2 X 8 single stimuli (120 & 150% motor threshold (MT)), and 8 paired- pulse stimuli with four different interstimulus intervals (ISI): 2, 3, 10, and 15 ms in randomized order (Conditioning stimulus: 80% MT, test stimulus: 120% MT). The first dorsal interosseous muscle (FDI) served as control. Changes in tongue-training success rate from the first 3 min to the last 3 min were calculated. Absolute (single MEPs) and normalized (ppTMS) data were analyzed with repeated measurement ANOVAs. Correlation analyses were performed between changes in success rate and changes in MEP, SICI, and ICF. Results: No differences in single MEPs were found between sides but a tendency towards lower amplitudes on the ipsilateral side was seen (P 5 0.11). In tongue motor cortex, no significant SICI (P . 0.466) but clear ICF was detected before and after training (P , 0.031). There were no effects of training on single MEPs, SICI, or ICF in tongue or FDI motor cortex (P . 0.151). The success rate improved significantly from 16 1 2% to 26 1 2% during training (P , 0.001) and changes in success rate were positively correlated to changes in single MEP-amplitude (P , 0.014) but not to SICI/ICF (P . 0.194). Conclusion: This first study of bilateral SICI/ICF after a tongue-training task showed no changes in intracortical inhibitory or facilitatory networks. However, there was an association between task performance and changes in corticomotor excitability assessed by single-TMS supporting previous observations of short-term plasticity in corticomotor control of tongue muscles. Clinical Studies Poster Only 102 Cortical excitability and interhemispheric inhibition in subcortical pediatric stroke: Chronic reorganization and effects of contralesional inhibitory rTMS Kirton A 1 , deVeber G 2 , Gunraj C 3 , Friefeld S 2 , Chen R 3 , 1 Alberta Children’s Hospital (Calgary, CA); 2 Hospital for Sick Children (Toronto, CA); 3 Toronto Western Research Institute (Toronto, CA) Objective: Arterial ischemic stroke (AIS) causes neurological disability in children. Subcortical lesions are common but TMS studies of their plastic reorganization have not been done. Imbalance of interhemispheric inhibi- tion (IHI) is associated with poor motor outcome in adult subcortical stroke and represents a potential therapeutic target. We hypothesized that IHI from normal to stroke hemisphere (IHINS) is excessive in children with chronic subcortical stroke and can be reduced by daily inhibitory rTMS. Methods: Eligible SickKids Children’s Stroke Program patients included: (1) subcortical AIS with transcallosal pathway sparing, (2) age .7years and post-stroke interval .2yrs, (3) hand motor impairment, and (4) no seizures, dyskinesia, or medications. TMS was performed using figure- eight coils with surface electromyography recorded from the first dorsal interosseous (FDI) muscle bilaterally. Baseline measures included rest and 1mV motor thresholds and a stimulus response curve (SRC) from 100- 150% RMT. A paired-pulse method with interstimulus intervals (ISI) of 10 and 40ms studied bidirectional IHI. Children were matched for age and weakness and randomized to contralesional inhibitory rTMS (1Hz, 20min, 1200 stimuli) or sham for 8 days after which neurophysiological measures were repeated. Results: Ten children were enrolled (median 12.4yrs, 4 female) with unilateral hand weakness of mild (4), moderate (2), or severe (4) intensity. Motor thresholds were increased over the stroked hemisphere (RMT 76.1 vs 54.1, p , 0.01) and decreased with age (r2 5 0.892). Baseline IHINS was evident at both 10ms (-17%) and 40ms (-46%). IHISN was signifi- cantly less at both 10ms (14%, p 5 0.02) and 40 ms (-28%, p 5 0.05). Following inhibitory rTMS, motor thresholds were unaltered but maximal stroke side MEP amplitudes increased in treated patients (11.52 versus 10.09 mV, p 5 0.01). SRC slope increased in rTMS patients (0.82 from 0.48, p 5 0.02). IHINS appeared to decrease from baseline in treated chil- dren at 10 (114%) and 40 ms (-15%) while IHISN appeared increased (10ms -13%, 40ms -40%). In the sham group, IHINS and IHISN were comparable to baseline but changes did not significantly differ from the rTMS group (p . 0.15). Conclusion: TMS measurement of plastic reorganization is feasible in children with chronic stroke. Preliminary evidence supports the IHI imbal- ance model in children and offers a potential target for neurorehabilitation. TMS Poster Only 103 Task-dependent modulation of short-latency intracortical inhibition and TMS-evoked EMG suppression Zuur AT 1 , Perez MA 2 , Sinkjær T 1 , Nielsen JB 2 , Grey MJ 2 , 1 Aalborg University (Aalborg, DK); 2 University of Copenhagen (København, DK) Objective: Transcranial Magnetic Stimulation (TMS) applied over the motor cortex can evoke excitatory and inhibitory effects. Short-latency intracortical inhibition (SICI; Kujirai et al.,1993) and TMS-evoked EMG suppression (Davey et al.,1994) are both thought to be related to the excitability of intracortical interneurons projecting to corticospinal neu- rons. The objective of this study was to describe the modulation of these two inhibitory effects during different tasks. Methods: Subjects performed three different tasks during this experiment: seated isometric soleus(SOL) contraction, walking and standing. TMS was Abstracts 271