Slowed cognitive processing and high workload in Parkinson's disease

It is suggested that cognitive slowing in Parkinson's disease (PD) may be evident on a task with high cognitive load. This hypothesis was tested using a workload design with a progressive increase in task difficulty, on a group of Parkinson patients and normal controls. Using measures of Reaction Time (RT) and Event Related Potentials (ERP), results showed that RT and ERP waveforms increased in line with task difficulty. The RT data was not significantly different between groups but the ERP showed a much reduced P300 in the patient group. These results are indicative of cognitive slowing in PD, at the stage of stimulus evaluation but not for response selection. An interpretation of the literature in terms of reduced activation in relation to cognitive slowing is discussed.