Effect of interstimulus interval on visual P300 in Parkinson's disease

Objective-Visual event related potentials (ERPs) were studied during an odd ball paradigm, to testify whether cognitive slowing in Parkinson's disease exists and to investigate whether cognitive information processing can be i nfluenced by different interstimulus intervals (ISIs) of an oddball task in patients with Parkinson's disease and normal subjects. Methods-ERPs and reaction time were measured in 38 non-demented patients wi th Parkinson's disease and 24 healthy elderly subjects. A visual oddball pa radigm was employed to evoke ERPs, at three different interstimulus (ISI) i ntervals: ISI(S), 1600 ms; ISI(M), 3100 ms; and ISI(L), 5100 ms. The effect of ISIs on ERPs and reaction time was investigated. Results-Compared with the normal subjects, P300 latency at Cz and Pz was si gnificantly delayed after rare target stimuli in patients with Parkinson's disease only at ISI(L). Reaction time was prolonged in patients at all the three ISIs, compared with the normal controls. There was also significantly delayed N200 and reduced P300 amplitude at Cz and/or Pz to rare non-target stimuli in patients at the three ISIs, compared with the normal controls. During rare target visual stimulation, P300 latency and reaction time in th e patients with Parkinson's disease and reaction time in the normal subject s were gradually prolonged as the ISI increased. Conclusion-Prolonged N200 latency to rare non-target stimuli might indicate that automatic cognitive processing was slowed in Parkinson's disease. Cog nitive processing reflected by P300 latency to rare target stimuli was infl uenced by longer ISI in patients with Parkinson's disease.