Pathophysiological Insights Into STN DBS for Primary Cervical Dystonia

Subjects will participate in 1-3 visits, based on eligibility, as described below:

Study Visit 1: Baseline

• This visit applies to subjects with cervical dystonia who are planning DBS surgery in the next 1-4 weeks
• This visit applies to subjects with cervical dystonia who are not planning DBS surgery
• This visit (except #3) applies to healthy control subjects; this is the only visit for healthy control subjects

1. A neurological examination with special attention to the sensory system will be performed. The sensory system is the system by which the brain receives and perceives feelings from different parts of the body.
2. Women of child-bearing potential will be given a urine pregnancy test to evaluate pregnancy status.
3. DYSTONIA SUBJECTS ONLY: Clinical assessment of dystonia will be performed by administering several scales and measures, including: the Toronto Western Cervical Dystonia Rating Scale (TWSTRS), the Short Form (SF-36) scale for quality of life assessment, Visual Analog Scale (VAS) for assessment of dystonia and pain severity, the Mini Mental Status Examination (MMSE) for cognitive testing, and the Beck Depression Inventory (BDI II), for evaluation of mood.
4. We will determine your individual motor evoked potential (MEP) threshold before beginning the study treatment. Your MEP will be recorded from a muscle located between the right thumb and index finger on your right hand, and then on your left hand. MEP threshold refers to the amount of stimulation to the brain that is required to activate muscle cells enough to appear on an electromyography (EMG), which records electrical potential in muscle through electrodes placed on the skin.
5. We will test your sensory system and its interaction with the motor cortex by using transcranial magnetic Stimulation (TMS). For these tests, you will sit in a chair that looks like one you would find at the dentist's office. A nerve stimulator will be placed at the wrist of your right hand to stimulate the median and ulnar nerves. The intensity of the nerve stimulator will be gradually increased until the right thumb begins to twitch. A magnetic coil will be placed on the scalp on the left side of your head, overlying the brain's motor cortex, to stimulate the brain's output to the muscles in the opposite hand. This procedure will be repeated using the left wrist and the right side of your head.
6. We will spend an additional 30 minutes performing a protocol that allows for testing of plasticity changes in the brain. This protocol is called paired associative stimulation (PAS). The median nerve in your wrist and the TMS coil over your head undergo repeated paired stimulation. Such repeated pairing builds plasticity effect in the motor cortex. MEP, as explained earlier, is recorded before and after this protocol.
7. Subjects who have provided consent will be videotaped during this visit.

Study Visit 2: