The Role of Prefrontal and Posterior Parietal Cortex in Generating Multiple Step Saccades.

While multiple step saccades (MSS) are occasionally reported in the healthy population, they are more evident in patients with Parkinson's disease (PD). Therefore, MSS has been suggested as a biological marker for the diagnosis of PD. However, the lack of clarity on the neural mechanism underlying the generation of MSS largely impedes their application in the clinic. We have proposed recently that MSS are triggered by the discrepancy between desired and executed saccades. Accordingly, brain regions involved in saccadic planning and execution might play a role in the generation of MSS. To test this hypothesis, we explored the role of the prefrontal (PFC) and posterior parietal cortex (PPC) in generating MSS by conducting two experiments: electroencephalographic recording and single-pulse transcranial magnetic stimulation in the PFC or PPC of humans while participants were performing a gap saccade task. We found that the PFC and PPC are involved in the generation of MSS.