The Effects of Subthalamic Nucleus Deep Brain Stimulation in Parkinson's Disease on Associative Learning of Verbal and Non-Verbal Information by Trial and Error or with Corrective Feedback.

BACKGROUND: Parkinson's disease (PD) and subthalamic nucleus deep brain stimulation (STN-DBS) are both known to induce cognitive changes. OBJECTIVE: The aim of our study was to investigate the impact of STN-DBS on two forms of conditional associative learning (CAL), trial and error or corrective feedback learning, which differed in difficulty to test the load-dependency hypothesis of the cognitive effects of STN-DBS in PD. METHODS: We recruited two groups of PD patients, those who had STN-DBS surgery bilaterally (n = 24) and a second unoperated group (n = 9) who were assessed on two versions of a task of visual CAL involving either a more difficult trial and error learning or a relatively easier corrective feedback learning. Each task was completed twice by both groups, On and Off STN-DBS for the operated group and a first and second time by the unoperated group. RESULTS: With STN-DBS Off, corrective feedback learning was superior to trial and error CAL, but not with STN-DBS On. The unoperated PD group had improved performance during the second assessment. To control for the improvement observed with repeated assessment in the PD control group, we split the STN-DBS group into two subgroups based on the condition of the first assessment (Off first vs. On first). While we found no STN-DBS effects for the Off first subgroup (N = 14), we observed improved performance during the second STN-DBS Off session for the On first subgroup (N = 10). CONCLUSION: The findings suggest that in PD, STN-DBS interferes with use of corrective feedback and its integration in the conditional associative learning process. Also STN stimulation affected the ability of operated patients to resolve proactive interference during learning of the arbitrary visual associations by trial and error or with corrective feedback.