The purpose of this research study is to test the safety and effectiveness of the study drug, Talampanel, when used to treat patients with involuntary movements known as dyskinesias, as a result of treatment to Parkinson's disease.

It is not clear why people with Parkinson's disease develop involuntary movements (dyskinesias) but studies show that blocking receptors in the brain for a chemical called glutamate decreases these movements. Talampanel is a drug which blocks these receptors.

Inclusion Criteria:

• Troublesome on-period dyskinesias as defined by a Unified Parkinson's Disease Rating Scale (UPDRS) dyskinesia sub-score >25% of Duration of dyskinesia during waking hours and 33 must have moderate disability
• Lang-Fahn dyskinesia rating score more than 2 for at least two of the 5 tasks
• Must have Dyskinesia on average 25% of waking hours/day based on Patient Diaries
• Have been diagnosed with Parkinson's disease > 5 years at Screening

Exclusion Criteria:

• Previous surgical therapies for PD
• Isolated or predominantly diphasic dyskinesias
• Moderate Dementia
• On disallowed concomitant medications including CYP3A4 inhibitors and inducers, amantadine, etc.