Orbital and ventromedial prefrontal cortex functioning in Parkinson's disease: neuropsychological evidence

A recent paper (Zald & Andreotti, 2010) reviewed neuropsychological tasks that assess the function of the orbital and ventromedial portions of the prefrontal cortex (OMPFC). Neuropathological studies have shown that the function of the OMPFC should be preserved in the early stages of Parkinson's disease (PD) but becomes affected in the advanced stages of PD. This pattern has also been suggested by studies that have shown that dopaminergic drugs impair the performance of early PD patients in OMPFC tasks that involve reinforcement learning but enhance the performance of advanced PD patients. Based on these empirical findings, we reviewed the neuropsychological evidence of OMPFC functions in PD patients to test two hypotheses regarding the following: (1) OMPFC functions at different stages of PD; (2) different effects of dopaminergic drugs on OMPFC functions based on PD stage and task demand. We focused our review only on the neuropsychological tasks that were specific and sensitive to the functions of the OMPFC and that were adopted at different stages of PD, such as reversal learning tasks, the Iowa Gambling Task and the affective Theory of Mind task. We found robust empirical evidence that in early PD, OMPFC functions are preserved and dopaminergic drugs result in a detrimental effect when the task involves reinforcement learning. Further studies are needed to verify the status of OMPFC functions in non-demented, advanced PD and to describe the longitudinal course of OMPFC functions in this clinical population.