The role of the striatum and hippocampus in planning - A PET activation study in Parkinson's disease

Previous work has identified the prefrontal cortex (PFC) and striatum as pa rticipating in the planning and selection of movements. We compared the bra in activation patterns during planning in Parkinson's disease patients and age-matched controls using (H2O)-O-15- PET and the Tower of London (TOL) ta sk. In this study, our mildly affected Parkinson's disease group performed as well as the control group but showed a different pattern of neuronal act ivation. In the two groups, overlapping areas of the PFC were activated but , whereas the right caudate nucleus was activated in the control group, thi s was not evident in the Parkinson's disease patients. This suggests that n ormal normal frontal lobe activation can occur in Parkinson's disease despi te abnormal processing within the basal ganglia. Moreover, right hippocampu s activity was suppressed in the controls and enhanced in the Parkinson's d isease patients. This could represent a shift to the declarative memory sys tem in Parkinson's disease during performance of the TOL task, possibly res ulting from insufficient working memory capacity within the frontostriatal system.