Motor disturbance and brain functional imaging in Parkinson's disease.

18F-Dopa positron emission tomography (PET) provides a sensitive means of quantitating the loss of nigrostriatal dopaminergic fibres in Parkinson's disease and so can be used to diagnose its presence and to objectively follow the rate of disease progression. It can also be used, in principle, to determine the efficacy of putative neuroprotective agents and has already been extensively used to monitor the viability of striatal transplants of fetal mesencephalic tissue. Loss of dopaminergic projections produces significant changes in the patterns of both resting and activated cortical function. H2(15)O PET activation studies have suggested that the akinesia of Parkinson's disease is associated with failure to activate the supplementary motor and dorsal prefrontal areas, brain regions particularly involved in motor preparation and decision making. Activation of these cortical areas can be restored by administering dopaminergic medication, implanting the striatum with fetal mesencephalic tissue, and by pallidotomy. This article reviews the insight that PET studies have provided into the pathophysiology of Parkinson's disease.