The Characteristics of Sequence Effect in de Novo and Advanced Parkinson's Disease

This study will explore sequence effect, a fatigue or tiredness commonly seen in patients with Parkinson's disease after they have been doing the same thing for a while. The study will use a new device called a modified peg board test (see description below) to measure whether antiparkinsonian medications (levodopa/carbidopa or dopamine) and repetitive transcranial magnetic stimulation (rTMS, see description below) of the brain can improve the symptoms of sequence effect.

Patients with early-stage Parkinson's disease who have never taken antiparkinsonian medications and patients with advanced disease may be eligible for this study. Candidates must be 18 years of age or older and right-handed.

Participants have five visits to the NIH Clinical Center as follows:

• Visit 1 (baseline): Patients have a neurological examination, including brief cognitive function tests, a rating for depression, and two types of ratings for fatigue severity.
• Visits 2 through 5 (experimental sessions): Patients who have been taking antiparkinson medication for a long time are asked to not take their medication for about 12 hours (overnight withdrawal) before visits 2 through 5. They are off medication for about 14 hours total (until after the experiments are done). Patients may be admitted to the NIH Clinical Center for the overnight drug withdrawal if necessary. At the start of each session, participants are given either levodopa/carbidopa tablets or placebo (tablets identical in appearance but with no active medication). They perform the modified pegboard test before medication, after medication, and after brain stimulation with rTMS. During two of the sessions, they receive actual brain stimulation, and during the other two sessions they receive sham stimulation, which does not actually stimulate the brain.

The modified pegboard test is a computer-based machine with eight pegs. Subjects transfer each peg from a line of holes on the right side to a line of holes on the left side using their right hand and moving as quickly as possible. After they finish moving all pegs to the left line of holes, they wait for a beep and then transfer the pegs from left line to right line of holes. They do this six times, three times with their right hand and three times with their left.

rTMS involves repeated magnetic pulses delivered in trains or short bursts of impulses. A brief electrical current is passed through a wire coil held on the scalp. The current creates a magnetic pulse that stimulates the brain. The subject hears a click and may feel a pulling sensation on the skin under the coil. There may be a twitch in muscles of the face, arm or leg. During the stimulation, the subject may be asked to tense certain muscles slightly or perform other simple actions. The effect of TMS on the muscles is detected with small metal disk electrodes taped onto the skin of the right hand. Subjects receive four rTMS blocks per 10 minutes. Each block consists of a total of 375 pulses.