Plasticity in Cervical Dystonia

Objectives The main objective of this proposal is to evaluate plasticity in patients with cervical dystonia. Neither abnormal Hebbian nor non-Hebbian plasticity has been studied for cervical dystonia. Our specific objectives are to show that: 1. In patients with cervical dystonia, Hebbian plasticity can be induced by using paired associative stimulation (PAS) of the dystonic sternocleidomastoid muscle (SCM) muscle and will be enhanced compared to that of healthy subjects. 2. In patients with cervical dystonia, non-Hebbian plasticity can be induced by using transcutaneous electrical nerve stimulation (TENS) of the dystonic SCM muscle and will be enhanced compared to that of healthy subjects. 3. In patients with cervical dystonia, Hebbian and non-Hebbian plasticity can be induced by dual stimulation (DS) of the dystonic SCM muscle, this effect will be greater than PAS or TENS alone, and it will be enhanced compared to that of healthy subjects. Study Population We will study 22 patients with cervical dystonia and 22 healthy subjects for a total of 44 subjects. Study Design Subjects will participate in 4 different sessions: Visit 1: clinical screening (1 hour) and sensory evoked potential (SEP) assessment (2 hours, total of 3 hours). Visit 2: PAS session of the target muscle and monitoring of cortical excitability before (T0), immediately after (T1), 45 minutes after (T2) and 90 minutes after T(3) (Total of 4 hours). Visit 3: TENS session of the target muscle and monitoring of cortical excitability before (T0), immediately after (T1), 45 minutes after (T2) and 90 minutes after T(3) (Total of 4 hours). Visit 4: DS session of the target and monitoring of cortical excitability before (T0), immediately after (T1), 45 minutes after (T2) and 90 minutes after T(3) (Total of 4 hours). Outcome Measures The electrophysiological effects of the interventions will be assessed by the size of motor evoked potentials (MEP), resting and active motor threshold (RMT and AMT), and a transcranial magnetic stimulation (TMS) input-output curve. The activity of intracortical interneurons mediating long intracortical inhibition (LICI) will be assessed by paired-pulse TMS. The effect of afferent input on intracortical processes (long afferent inhibition, LAI) will be assessed by stimulating the skin overlying the sternocleidomastoid muscle (SCM).