STN-DBS Increases Proactive but Not Retroactive Interference During Verbal Learning in PD

Patterns of proactive interference in CVLT-II: evidence of a low-organized, disorganized, and highly organized learning style

OBJECTIVE

Previous studies have interpreted proactive interference (PI) either as indicating executive dysfunction or a normal process indicating deep level encoding. We investigated these competing models of PI in a large clinical sample using cluster analyses. We expected to find clusters defined by high PI but otherwise characterized by either EF impairment or of good memory performance.

METHOD

File records of 731 patients with neurological or psychiatric disorders were analyzed. PI-scores, false positive recognition errors, and semantic organization scores on the California Verbal Learning Test-II (CVLT-II) were subjected to cluster analyses. Clusters were compared regarding buildup and release from PI, memory performance and strategy measures, measures of intelligence, EF, and processing speed.

RESULTS

The analyses revealed six analyzable clusters. Two clusters showed no buildup of PI and normal release from PI. Discriminability was impaired both in List A and B. Learning acquisition and speeded measures of EF were reduced. One cluster showed both buildup of PI and problems with releasing from PI, and particularly impaired discriminability of List B. Semantic organization was low. Learning consolidation and EF speeded measures were impaired. Two other clusters showed buildup of PI, but no problem with release. Learning was highly organized, and they showed good memory and normal neuropsychological performance.

CONCLUSIONS

Results shows differentiation between a low organized EF dysfunction pattern with no PI, a disorganized PI pattern also indicating EF dysfunction and a highly organized pattern where PI seems to be the price to pay for high effort put into the learning process.

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.