Applied strategy in the Iowa Gambling Task: Comparison of individuals with Parkinson's disease to healthy controls.

Introduction: Decision-making impairments in Parkinson's disease (PD) have frequently been measured using the Iowa Gambling Task (IGT), though results have been inconsistent. At present, task performance has primarily been evaluated based on the total IGT score, and there is a need for further analysis of the strategy of older individuals with PD and healthy control (HC) participants in IGT.

Objective: The present study aims to explore possible impairments in IGT performance in individuals with PD compared to healthy controls using strategy analysis, extending previous results on this subject, and to discuss potential effects of medication on task performance.

Methods: 67 individuals with PD and 29 HC participants completed the IGT. Results were analyzed to evaluate impairments, applied strategies, presence of subgroups, and potential effects of medication on performance.

Results: Both groups obtained a low overall IGT score and individuals with PD had significantly lower total IGT scores compared to HC participants. Regression analysis showed a small, but significant relationship between levodopa and dopamine agonist dosage and total IGT score, indicating that medication level could be a marker of level of executive functions. Subgroups of advantageous and disadvantageous choosers differed significantly in deck preferences for both groups.

Conclusion: Individuals with PD were significantly impaired in IGT performance, both in overall scores and in detailed analyses, and they utilized an inefficient strategy during task performance. However, HC participants also presented with a suboptimal strategy and results suggest the presence of subgroups in both individuals with PD and HC participants, which may reflect age-related changes. These results are in line with previous research on performance of older individuals and alternative deck preferences in the IGT and underline the importance of considering the applied strategy in the evaluation of IGT performance.