Objective: Examine the effect of task difficulty on event-related potentials (ERPs) in an oddball task in patients with PD.

Background: In three-stimulus oddball tasks, some studies have found a decrease in P300 latency for PD patients compared to HC, but others have reported an increased P300 latency. Similarly, there are mixed findings for P300 amplitude. This variability could be due to methodological differences. Studies in HC have shown that increasing task difficulty leads to prolonged P300 latency and reduced amplitude, but the effect of task difficulty on P300 latency in PD is not known.

Method: Nine PD patients were recruited who had relatively normal cognitive status (non-MCI). Twelve age-matched HC were also recruited. Two levels of difficulty of a three-stimulus visual oddball task were used and test order counterbalanced across participants. In one version, the target stimuli (8% of trials) was 60% of the standard (84 % of trials) and distractor (8% of trials) stimulus size, and stimulus duration was 300 ms; in the second version, the target stimuli was 82% of the standard and distractor stimuli, using 80 ms stimulus duration. A button press was required for the target. The primary outcome measure was the P300 ERP at the Cz electrode.

Results: The PD group was on average 70 ms slower than the HC group to respond to the target (p=0.013), but response latency was not associated with task difficulty (main effect and interaction, p>0.5). P300 latencies were shorter for PD patients than HC for both target (by 50 ms, p<0.04) and distractor (66 ms, p<0.01), irrespective of task difficulty (Group x difficulty; p=0.17 and p>0.5). No effects were found, however, for P300 amplitude.

Conclusion: PD patients with relatively intact cognition have shorter P300 latencies to the infrequent target and distracter stimuli in a three-stimulus oddball task irrespective of difficulty in terms of relative stimulus size and duration. This may reflect the use of more focused attention to compensate for their reduced motor skills in these cognitively intact patients. Other factors, such as the inclusion of patients with mild or severe cognitive impairment, stimulus modality[JD1] or other task demands, may explain the variable ERP findings for PD patients in previous 3-stimulus oddball tasks.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/task-difficulty-and-the-three-stimulus-oddball-task-in-patients-with-pd/