This study will examine the effects of transcranial direct current stimulation (tDCS) on gait (walking) problems and rigidity in patients with Parkinson's disease. tDCS is a method of brain stimulation that may be able to change the electrical activity of the nerves of the brain, possibly causing Parkinson's disease symptoms to improve.

Patients between 40 and 80 years of age with moderately severe Parkinson's disease whose main symptoms are problems with walking, including freezing, or rigidity, may be eligible for this study. Candidates must be taking Sinemet or another L-DOPA drug and not have too much tremor.

Participants will be assigned to receive either real or sham (placebo) tDCS. Both groups will have eight treatments over 3-1/2 weeks. For the tDCS, electrodes are placed on wet pads on the scalp. An electrical current passes through the electrodes, travels through the scalp and skull, and causes small electrical currents in the cortex-the outer part of the brain. Participants will have a neurological examination, including an evaluation of walking, just before and just after each tDCS session. Patients' motor function will be re-evaluated at 1, 3, and 6 months after the last tDCS treatment.

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The treatment of Parkinson's disease (PD) needs further improvement, particularly in the areas of gait and freezing. Transcranial direct current stimulation (tDCS) which passes weak direct current (DC) current through the skull and across the cortex has been done for many years with numerous effects described in healthy subjects and patients with mental illness. Recently, it has been shown by objective means, in controlled experiments, that this type of treatment has robust and lasting effects on the excitability of the motor cortex in healthy humans. We hypothesize that tDCS will have a beneficial effect on gait and freezing in medicated patients, and we propose to test this in a controlled trial. Specifically, we propose to look at the effect of 1-2 mA tDCS with anode position over the frontal poles and/or premotor and primary motor cortex, and cathode over mastoid process. Over a one-year period, we will enroll 42 adults with PD and evaluate the acute tDCS effects over a period of four weeks (eight tDCS sessions, nine visits). Additional ratings will be done at one and three months after the end of tDCS sessions. Symptoms will be evaluated with standard tests of motor function, including the Unified Parkinson's Disease Rating Scale (UPDRS) and specific tests of gait and freezing. We will also look for cumulative, long-lasting effects over the three-month period.

• INCLUSION CRITERIA:

Patients with PD corresponding to inclusion criteria will be recruited from the Human Motor Control Section Clinic (HMCS).

Subjects will be men and women aged 40-80 years with DOPA-responsive, akinetic-rigid PD.

Patients who have never participated in HMCS protocols for PD will be interviewed and examined by either the principal investigator or a physician from the Brain Stimulation Unit or HMCS in order to establish the diagnosis of PD and rule out any neurological condition. Only patients with a Hoehm and Yahr grade of 2 to 4 while "off" will be accepted.

Patients must be on a regimen including levodopa. The total dose of levodopa and dopamine agonists (using dopamine equivalents) has to be equal to or more than 375 milligrams per day. Other anti-parkinsonian medications are also acceptable.

Patients should have problems with walking, including freezing, so that their gait time for a 10-meter distance will be six seconds or more.

EXCLUSION CRITERIA:

Exclusion criteria are any significant medical or psychiatric illnesses (except those symptoms often associated with PD or levodopa therapy, such as sundowning and benign hallucination), pallidotomy, implanted electrodes and generator for deep brain stimulation, pregnancy.

Persons with surgically or traumatically implanted foreign bodies such as a pacemaker, implanted medical pump, implanted hearing aids, metal plate in the skull, or metal implant in the skull or eyes (other than dental appliances or fillings) that may pose a physical hazard during TEP will also be excluded. Most of these exclusions also come under the category of significant medical illness.

Patients for whom participation in the study would, in the opinion of the investigators, cause undue risk or stress for reasons such as tendency to fall, excessive fatigue, general frailty, or excessive apprehensiveness will also be excluded.

Patients unable to walk a 10-meter distance will be excluded.

Mentally impaired patients having no capacity to provide their own consent will be excluded from the study.