Comparing Stop Signal Reaction Times in Alzheimer's and Parkinson's Disease

To investigate the relative contributions of cerebral cortex and basal ganglia to movement stopping, we tested the optimum combination Stop Signal Reaction Time (ocSSRT) and median visual reaction time (RT) in patients with Alzheimer's disease (AD) and Parkinson's disease (PD) and compared values with data from healthy controls.

Thirty-five PD patients, 22 AD patients, and 29 healthy controls were recruited to this study. RT and ocSSRT were measured using a hand-held battery-operated electronic box through a stop signal paradigm.

The mean ocSSRT was found to be 309 ms, 368 ms, and 265 ms in AD, PD, and healthy controls, respectively, and significantly prolonged in PD compared to healthy controls (p = 0.001). The ocSSRT but not RT could separate AD from PD patients (p = 0.022).

Our data suggest that subcortical networks encompassing dopaminergic pathways in the basal ganglia play a more important role than cortical networks in movement-stopping. Combining ocSSRT with other putative indices or biomarkers of AD (and other dementias) could increase the accuracy of early diagnosis.