Inclusion Criteria:  PD as defined by the UK Brain Bank Criteria Disease duration between 2-13 years Aged 35-68 years Hoehn & Yahr stage 3 or less when in the levodopa-"ON" state  Exclusion Criteria:  Atypical parkinsonism including 18F-dopa PET patterns consistent with this MMSE score of < 24 or evidence for dementia using DSM-IV criteria Unable to do normal copying of interlocking pentagons and semantic fluency score <20 over 90 secs Ongoing major medical or psychiatric disorder including depression and psychosis Other concomitant treatment with neuroleptics Significant drug induced dyskinesias (>2 for any body part on the AIMS scale) Previous neurosurgery Unable to be imaged using MRI