Movement Disorders Poster Only 206 Joint coordination studied by TMS in focal hand dystonia Boyadjian A, Tyc F, Allam N, Brasil-Neto JP, Laboratoire plasticite ´& physio-patholog (Marseille Cedex, FR) Writer’s cramp belongs to a group of focal task-specific dystonias affecting fine manual skills and is characterized by excessive muscular activation during writing. Different TMS protocols have shown that the functional characteristics of cortical networks in motor areas were different in dystonic patients than control subjects. Furthermore, cortical activity during the movement preparation is different in dystonic patients, which could be responsible for a modification of the response of cells to afferent inputs and then the production of movement. The properties of neural excitability have to be considered in the context of muscle coordination. Our work focused on the integrated neural networks linking proximal and distal muscles that move the shoulder, the wrist and the finger. Such networks linking shoulder and wrist were observed in control subjects. We wanted to observe in dystonic patients the properties of response in different coordination condition to know how muscles are linked. Motor evoked potentials (MEPs) were recorded from medial deltoid (MD), extensor carpi radialis (ECR) and the first dorsal interosseus (FDI) muscles in 10 patients with focal hand dystonia and six healthy subjects. The subjects had to maintain a ring in order to do not touch a wire passing through this ring. The first condition was to maintain the ring using only the arm (ECR Alone), the elbow rested on an armrest. The second condition was to maintain the ring using the whole upper limb (ECR and MD co-activated). The TMS was done on the hot spot of the ECR with seven increasing intensities of stimulation, determined as percentages of the ECR active motor threshold (aMT). At each intensity, four stimulations were done and the corresponding MEPs averaged to compute excitability curves for the three muscles. Each group exhibited MEPs facilitation of ECR during the voluntary activation of MD as showed by plateau and slope of sigmoid regression. Interestingly only the patient group showed facilitation of FDI when MD was activated. Then, in dystonic patients, even the ‘‘most’’ distal part of muscle chain could be facilitated by the ‘‘most’’ proximal part of the upper limb. The generalization of neural pathways though to allow the coordi- nation between each joint could be responsible of an excess in tonic activity resulting in an inadequate pattern of coordination observed in dystonic patients during writing. Clinical Studies Poster Only 207 Cortico-cortical properties in Parsonage-Turner Syndrome: a TMS case study Rossi-Durand C, Boyadjian A, Devanne H, Tyc F, Laboratoire plasticite ´ & physio-patholog (Marseille Cedex, FR) We report the long-term effects of one unilateral Parsonage-Turner Syndrome case (PTS) on motor cortex representation of a proximal upper limb muscle. The subject suffered from a sporadic painful episode of weakness of the shoulder girdle muscles seven years earlier. At this time, needle EMG recordings showed only few MUs in the left anterior deltoid muscle (AD), while nerve conduction was found normal. Arthroscanner examination was unremarkable confirming the absence of joint lesion. The episode lasted for one year. Currently, the PTS-subject uses his left arm without any limitation in strength and accuracy. Bilateral transcranial magnetic stimulation mapping of proximal AD and distal First Dorsal Interosseus muscles (FDI) during low-level voluntary contraction showed that cortical representation of both the left AD and FDI muscles were smaller than the right ones and than those obtained in control subjects. Single motor unit potential analysis of AD muscle have shown a decrease in the probability of response to the single pulse TMS. Macro motor-unit potential analysis did not show any difference between right and left AD, suggesting an absence of motoneu- ron death. A decrease of single MU excitability associated with the absence of macro-MUP size variation has been considered as an index of dysfunction in cortico-spinal pathways in neurodegenerative pathology like amyotrophic lateral sclerosis. We hypothesized that seven years later, despite complete motor recovery, a functional modification of cortico- spinal pathway still persists. To test whether long-term modifications of cortico-cortical properties have occurred, we applied intermittent and continuous thetaburst stimulation (iTBS and cTBS) on each hemisphere. We have tested ECR and FDI. The data obtained with iTBS and cTBS showed that cortical mechanisms were different between pathological and non-pathological side. This suggests altered plasticity processes, which could explain the absence of recovery in muscle representation size. Finally, we have tested the influence of AD activity on ECR excitability to understand the normal coordination observed in the patient. ECR excitability curves were similar in both hemispheres showing that the cortical interaction between the AD and the ECR muscles. These results showed that cortical networks underlying muscle coordinations were preserved, which could explain the normal coordination observed in the PTS-subject, despite the small AD representation. Physiology Poster Only 208 The effects of two different repetitive TMS stimulation protocols on muscle fatigue associated changes in excitability of motor cortex in man Ljubisavljevic M 1 , Dhanasekaran S 1 , Maric J 2 , Blesic S 2 , Filipovic S 3 , 1 FMHS, UAE University (Al Ain, AE); 2 Institute for Medical research (Belgrade, RS); 3 Institute of Neurology CCS (Belgrade, RS) Objective: Muscle fatigue involves processes at all levels of the motor pathway between the brain and the muscle. Central fatigue represents the failure of the nervous system to drive the muscle optimally. When measured by transcranial magnetic stimulation (TMS) central fatigue appear as a decrease in corticospinal excitability after exercise. Repetitive transcranial magnetic stimulation (rTMS) can produce effects on cortico- spinal excitability that outlast the duration of the stimulation. The direction, magnitude and duration of effects critically depend on stimu- lation variables. We applied two rTMS protocols over M1 to test their influence on fatigue associated behavioral correlates (endurance time) and cortical excitability. Method: Low frequency [LF] (1 Hz for 20 min) and High frequency rTMS stimulation [HF] (5 Hz for 20 min) were applied in order to induce lasting decrease and increase in cortical excitability before fatigue, respectively. In the LF the TMS intensity was set to 95% of the first dorsal interosseous muscle (FDI) resting motor threshold (RMT) and in the HF protocol the TMS intensity was set to 110% of the RMT. Changes in cortical excitability after fatigue induced by continuous isometric abduction of the index finger against elastic resistance maintained at 50% of maximal voluntary contraction until endurance point were examined in 6 men. Result: Fatigue induced lasting decrease in cortical excitability. HF applied alone evoked lasting increase in MI excitability, while when applied before fatiguing contraction it reversed fatigue induced reduction in cortical excitability but had no effects on endurance time. LF applied alone decreased cortical excitability but when applied before fatigue it did not further influence fatigue related decrease in excitability. However, in 4 subjects the endurance time decreased by approximately 10%. Abstracts 305