Cervical dystonia (CD) is a common movement disorder. Despite the optimization of botulinum toxin injection (BoNT-A) parameters including muscle selection and dosing, a significant proportion of patients report low levels of satisfaction, and a few of them develop resistance to therapy. The only options for such patients would be invasive therapy such as pallidotomy or pallidal deep brain stimulation. Currently, studies are going on the effectiveness of noninvasive neurostimulation in different neurological disorders. Transcranial Direct Current Stimulation (tDCS) or transcranial pulsed current stimulation (tPCS) are known to be safe non-invasive intervention with almost no side effects that can be used to provide complementary treatment. To detect the dysfunctional regions five min resting state quantitative EEG (qEEG) eyes closed will be recorded and analyzed each time before and after noninvasive stimulation. The investigators will evaluate the efficacy of acute noninvasive stimulation in those CD patients who are already on 3 monthly BoNT-A therapy but the effect of BoNT-A is wearing off in 8 weeks. Kinematics (static and dynamic movements) of neck movements will be recorded using established technology before and after stimulation.

Cervical dystonia (CD) is the most common adult onset dystonia. Abnormal sensorimotor integration and maladaptive plasticity have been proposed as possible mechanisms. Currently, there is no definite way to assess and modify this dysfunctional network. Deep brain stimulation (DBS) is one possible way, but it is invasive and being used in highly selected patients. Intramuscular injections of botulinum toxin injection (BoNT-A) are successful. However, 30% patients discontinue due to lack of efficacy, side effects like muscle atrophy and dysphagia and the effect may wear off by week 8. Importantly, injections don't change the abnormal networks, as patients need life-long treatment.

Noninvasive brain stimulation (NIBS) is an evolving therapeutic option. Repetitive transcranial magnetic stimulation (rTMS) has already been used in network modulation in CD. Although effective, cost, lack of portability and side effects remain issues of rTMS. Portable, better tolerated and cheaper options using transcranial direct current stimulation (tDCS) in Parkinson's disease, dystonia, tremor, ataxia and transcranial pulsed current stimulation (tPCS) in Parkinson's disease are exciting new options. However, with these methods of NIS, many challenges remain - dysfunctional network localization, selecting parameters to use, providing adequate stimulation to alter the network consistently, maintain the therapeutic benefit chronically and have consistent adoption by the patient and clinician community. These variables make this exciting approach high risk, yet high yield if successful.

In this study, the investigators will use a new quantitative electroencephalography (qEEG) technique to first localize global network dysfunction in CD. Kinematic analysis of the biomechanics of CD will be recorded. The efficacy of acute NIBS will be evaluated in those CD patients who are already on 3 monthly BoNT-A therapy but the effect of BoNT-A is wearing off in 8 weeks.The effect will be measured using qEEG and kinematics pre and post stimulation.

Noninvasive stimulation will be delivered through a pair of saline-soaked (0.9% NaCl) surface sponge electrodes. Stimulation will be given for 20 mins, single session. For the sham condition, the electrode placement will be same, but the electric current will be ramped down in 5 seconds after the beginning of the stimulation.

Neurophysiological EEG signals will be recorded, eyes-closed, no-task, using g.Nautilus g.tec wireless system. The g.tech system uses earclip reference sensors. The subject will be in a quiet place with less light or electromagnetic perturbations. During the resting state recordings, patients are seated in a comfortable arm chair and will be instructed to keep relaxed, with their eyes closed for 5 mins.

A paired t test will be used to compare baseline data and post tPCS data. Descriptive analysis of the neurological examination findings will be provided.

Inclusion Criteria:

• Patients with cervical dystonia who are already on 3 monthly BoNT-A therapy but the effect of BoNT-A is wearing off in 8 weeks.

Exclusion Criteria:

• Patients who have other issues like known structural etiology, that can aggravate cervical dystonia
• Patients who are not able to provide informed consent