Cortical excitability depends on inhibitory mechanisms efficiency among which long latency intracortical inhibition (LICI) can be studied by paired pulses transcranial magnetic stimulation (TMS). Some recent evidences suggest that LICI may be one of the mechanisms by which the motor comment is adapted to the ongoing motor task with LICI strength being dependent on task complexity. In writer cramp and musician cramp, two forms of dystonia, the cortical excitability is not correctly modulated in some complex gestures. the hypothesis is that this task dependent perturbation of excitability in writer cramp could be due to a lack of LICI efficiency.

Inclusion Criteria:

• Patient with hand dystonia : writers cramp
• Subject affiliated to social security regimen.

For healthy volunteers :

• Healthy volunteer without neurological disorders based on sensorimotor examination.
• Subject affiliated to social security regimen.

Exclusion Criteria :

• Subject unable to receive informed consent (dementia).
• Contraindication to Transcranial Magnetic Stimulation(TMS) (epilepsia, intracranial metalic foreign object, hearing device, cochlear implant).
• Patient using a psychotrope treatment.
• Patient under guardianship or curatorship.
• Pregnant or nursing women.
• Patient with a cardiac stimulator.

For healthy volunteers only :

• Abnormal neurological evaluation based on sensorimotor examination or neurological history ( epilepsy, stroke ; brain or spinal cord surgery ; history of neurological disease affective sensitive and motor control)