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Angelo Quartarone,1 Sergio Bagnato,1 Vincenzo Rizzo,1 Hartwig R. Siebner,2 Vincenzo Dattola,1 Antonio Scalfari,1 Francesca Morgante,1 Fortunato Battaglia,1 Marcello Romano1 and Paolo Girlanda1

1Department of Neurosciences, Psychiatric and Anaesthesiological Sciences University of Messina, Italy and 2Department of Neurology, Christian-Albrechts- University, Kiel, Germany

Low-frequency median nerve stimulation, paired with suprathreshold transcranial magnetic stimulation (TMS) over the optimal site for activation of the abduc- tor pollicis brevis (APB) muscle induces a long-lasting increase in the excitability of corticospinal output neu- rons, if median nerve stimulation is given 25 ms before TMS. Here we employed this protocol of stimulation to assess associative plasticity of the primary motor hand area in 10 patients with writer’s cramp and 10 age- matched controls. Motor evoked potentials (MEPs) were recorded from right APB muscle and right ®rst dorsal interosseus (FDI) muscle. Resting and active motor threshold, mean MEP amplitude at rest, short- latency intracortical inhibition (SICI) at an interstimu- lus interval of 2 ms and the duration of the cortical silent period (CSP) were assessed immediately before and after associative stimulation. In both groups, asso- ciative stimulation led to an increase in resting MEP amplitudes which was more pronounced in the right.