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P20-13 Neuromodulation with paired-pulse TMS at interpulse intervals of 1.5 ms but not 2 ms increases corticospinal excitability
S222 association cortex (MAC) modifies excitability of the primary motor (M1) and somatosensory (S1) cortices via neuronal connectivity. Methods: Anodal, cathodal and sham tDCS over the left premotor areas to ten healthy adult subjects for 15 min on separate days. Both motor evoked potentials (MEPs) and somatosensory evoked potentials (SEPs) were recorded before, immediately after, and 15 min after tDCS. Anodal and cathodal tDCS were conducted using two sizes of stimulating electrodes (large: 4×4.5 cm/small: 3×3 cm). The accuracy of the electrode positions for the stimulated sites in the brain was evaluated in two of ten subjects. The electrode positions were overlaid on MRI anatomical surface images of each individual. Results: Following anodal tDCS by a large electrode, the amplitudes of MEPs significantly decreased, while those of SEP components (N20 and P25) were enhanced. The opposite effect on MEPs and N20 and P25 of SEPs was seen following cathodal tDCS stimulation. However, a small electrode did not significantly affect both M1 and S1 irrespective of the polarity. Both the large and the small electrodes covered mainly dorsal premotor area (PMd). Only the large electrode included the supplementary motor area (SMA), but did not reach to the ventral premotor area and the contralateral hemisphere. Conclusions: These results suggested that anodal tDCS over the MAC enhanced the inhibitory input to M1 and excitatory input to S1, but cathdal tDCS might lead to opposite behavior. The finding that only the large electrode modulated M1 and S1 implies that PMd activation along with SMA could be important to influence over primary sensori-motor areas. P20-12 Contextual interference benefits in motor sequence learning is associated with short and long-term changes in intracortical excitability A.D. Wu1,2 , P. Udompholkul1 , B.J. Knowlton3 , M. Iacoboni2,4 , C.J. Lin1 1 Department of Neurology, University of California Los Angeles, Los Angeles, California, USA, 2 Ahmanson-Lovelace Brain Mapping Center, UCLA, CA, USA, 3 Dept of Psychology, UCLA, CA, USA, 4 Dept of Psychiatry and Biobehavioral Sciences, UCLA, CA, UCLA Objective: To determine changes in short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) excitability associated with the contextual-interference (CI) effect, where practice of different tasks in random order results in superior retention learning compared to practice in blocked order. Methods:12 adults practiced serial reaction time tasks with three sets of 4-element sequences arranged in block or random order on Day 1 and Day 2 (acquisition). On Day 5 (retention), subjects were tested with practiced sequences. Each subject practiced under both blocked and random conditions in separate weeks in a within-subjects design. Pairedpulse TMS was applied over motor cortex with interstimulus intervals (ISI) of 2 5 msec (for SICI) and 10 15 msec (for ICF). Short-term effects of practice were assessed by comparing SICI/ICF before vs after each session of practice on Day 1 and 2. Long-term effects of practice were assessed by comparing pre-test SICI/ICF on Day 5 with pre-practice SICI/ICF on Day 1 and 2. Results: Consistent with the CI effect, random-practice reaction times (RT) were slower than blocked-practice RT during acquisition (effect size (ES) = 0.8), but random-retention RT was faster than blocked-retention RT on Day 5 (ES = 0.9). Short-term practice effects showed significant interaction with practice order for ICF (ISI = 15 ms) (p = 0.001); post-hoc testing showed that random practice increased ICF (p = 0.016) while block practice decreased ICF (p = 0.020) on Day 1. Long-term practice effects showed significant interaction with practice order for SICI (ISI = 4 ms) (p = 0.023) and ICF (ISI = 15 ms) (p = 0.001); post-hoc testing showed that random practice reduced SICI (p = 0.04) and increased ICF (p = 0.001) on Day 5. Conclusions: Immediate short-term effects of random-order practice increased ICF while block-order practice reduced ICF. However, improved retention learning, specific to random-practice, was associated with reduced SICI and increased ICF. Findings suggest that sequence learning may be supported by short-term and long-term changes to separate intracortical circuits.
Posters P20-13 Neuromodulation with paired-pulse TMS at interpulse intervals of 1.5 ms but not 2 ms increases corticospinal excitability R. Cash1 , F. Mastaglia1 , G. Thickbroom1 1 Centre for Neuromuscular and Neurological Disorders, University of Western Australia, Perth, Australia Objective: Repeated paired pulse TMS at 1.5 ms inter pulse interval (IPI), corresponding to indirect (I)-wave dynamics, has been shown to increase corticospinal excitability in the post-stimulation period (Cash et al., 2009). This is thought to operate via I wave facilitation, and to be analogous to spike timing dependent mechanisms of long-term potentiation (LTP) in which timing of pre and post synaptic events is critical. We hypothesised that an IPI that did not follow these events would either be ineffective or lead to a reduction in corticospinal excitability analogous to long term depression (LTD). Methods: Motor evoked potentials (MEPs) were recorded from the right first dorsal interosseous (FDI) muscle in six right handed subjects (21 27 years of age). The intervention comprised the delivery of paired pulse stimuli at an IPI of 2 ms every 5 s for 15 min (180 pairs). Cortico spinal excitability was measured using groups of ten single pulse (SP) stimuli delivered at baseline and post intervention for up to 20 mins. Results: At baseline, paired pulse MEP amplitude was 0.96±0.05 mV and 0.41±0.05 mV for IPIs of 1.5 and 2 ms respectively. For the period 2 10 minutes post intervention, SP MEP amplitude was reduced by 28% compared to baseline (1.09±0.14 mV vs. 0.76±0.13 mV; p < 0.05), but returned to baseline (0.99±0.12 mV) during the 10 20 min post period. Conclusion: A paired pulse TMS intervention delivered at a non I wave interval does not increase cortico spinal excitability, and may lead to a reduction in excitability in keeping with spike timing models of LTD. P20-14 Observation of healthy and pathological actions in the dystonic motor system: a TMS study M. Fiorio1 , W. Zhang2 , M.C. Bresciani1 , G. Rodi1 , L. Bertolasi1 , M. Gambarin1 , M. Tinazzi1,3 1 Department of Neurological, Neuropsychological, Morphological and Movement Sciences, University of Verona, Verona, Italy, 2 Tianjin Medical University General Hospital, Tianjin, China, 3 Neurology Unit, Borgo Trento Hospital, Verona, Italy Objectives: Observation of actions performed by other individuals activates the onlooker’s motor system in a way similar to real movement execution. The role of this mechanism in the neurorehabilitative setting is currently under investigation. The aim of this study was to explore whether action observation might facilitate the motor system of patients affected by a movement disorder, like focal-hand dystonia. Methods: To our purpose, we applied Transcranial Magnetic Stimulation on the primary motor cortex during observation of static images (a hand) and of actions (grasping, healthy writing and dystonic writing) in patients affected by writer’s cramp and in control subjects. Results: Results showed that patients, as well as control subjects, have higher corticospinal activation during the observation of writing actions compared to the observation of a static hand, suggesting that their motor system correctly resonates during action observation. Moreover, observation of healthy and dystonic writing actions equally activates the motor system of patients, whereas control subjects had higher activation during observation of dystonic compared to healthy actions. Conclusions: The corticospinal facilitation found in writer’s cramp patients during action observation might work as breeding ground to specifically modulate the motor system. Future research should tackle the issue of creating new motor memories in the dystonic primary motor cortex by means of an observational training in order to produce a favorable outcome on patients’ performance.
Posters P20-13 Neuromodulation with paired-pulse TMS at interpulse intervals of 1.5 ms but not 2 ms increases corticospinal excitability R. Cash1 , F. Mastaglia1 , G. Thickbroom1 1 Centre for Neuromuscular and Neurological Disorders, University of Western Australia, Perth, Australia Objective: Repeated paired pulse TMS at 1.5 ms inter pulse interval (IPI), corresponding to indirect (I)-wave dynamics, has been shown to increase corticospinal excitability in the post-stimulation period (Cash et al., 2009). This is thought to operate via I wave facilitation, and to be analogous to spike timing dependent mechanisms of long-term potentiation (LTP) in which timing of pre and post synaptic events is critical. We hypothesised that an IPI that did not follow these events would either be ineffective or lead to a reduction in corticospinal excitability analogous to long term depression (LTD). Methods: Motor evoked potentials (MEPs) were recorded from the right first dorsal interosseous (FDI) muscle in six right handed subjects (21 27 years of age). The intervention comprised the delivery of paired pulse stimuli at an IPI of 2 ms every 5 s for 15 min (180 pairs). Cortico spinal excitability was measured using groups of ten single pulse (SP) stimuli delivered at baseline and post intervention for up to 20 mins. Results: At baseline, paired pulse MEP amplitude was 0.96±0.05 mV and 0.41±0.05 mV for IPIs of 1.5 and 2 ms respectively. For the period 2 10 minutes post intervention, SP MEP amplitude was reduced by 28% compared to baseline (1.09±0.14 mV vs. 0.76±0.13 mV; p < 0.05), but returned to baseline (0.99±0.12 mV) during the 10 20 min post period. Conclusion: A paired pulse TMS intervention delivered at a non I wave interval does not increase cortico spinal excitability, and may lead to a reduction in excitability in keeping with spike timing models of LTD. P20-14 Observation of healthy and pathological actions in the dystonic motor system: a TMS study M. Fiorio1 , W. Zhang2 , M.C. Bresciani1 , G. Rodi1 , L. Bertolasi1 , M. Gambarin1 , M. Tinazzi1,3 1 Department of Neurological, Neuropsychological, Morphological and Movement Sciences, University of Verona, Verona, Italy, 2 Tianjin Medical University General Hospital, Tianjin, China, 3 Neurology Unit, Borgo Trento Hospital, Verona, Italy Objectives: Observation of actions performed by other individuals activates the onlooker’s motor system in a way similar to real movement execution. The role of this mechanism in the neurorehabilitative setting is currently under investigation. The aim of this study was to explore whether action observation might facilitate the motor system of patients affected by a movement disorder, like focal-hand dystonia. Methods: To our purpose, we applied Transcranial Magnetic Stimulation on the primary motor cortex during observation of static images (a hand) and of actions (grasping, healthy writing and dystonic writing) in patients affected by writer’s cramp and in control subjects. Results: Results showed that patients, as well as control subjects, have higher corticospinal activation during the observation of writing actions compared to the observation of a static hand, suggesting that their motor system correctly resonates during action observation. Moreover, observation of healthy and dystonic writing actions equally activates the motor system of patients, whereas control subjects had higher activation during observation of dystonic compared to healthy actions. Conclusions: The corticospinal facilitation found in writer’s cramp patients during action observation might work as breeding ground to specifically modulate the motor system. Future research should tackle the issue of creating new motor memories in the dystonic primary motor cortex by means of an observational training in order to produce a favorable outcome on patients’ performance.