Lack of neuropsychological effects following short-term subcallosal cingulate gyrus deep brain stimulation in treatment-resistant depression: a randomised crossover study.

Background: The subcallosal cingulate gyrus (SCG) is integral to cognitive function and mood regulation. Open-label SCG deep brain stimulation (DBS) studies demonstrate improvement or stabilisation of cognitive function in treatment-resistant depression (TRD).

Objective: This randomised controlled study aims to evaluate the neuropsychological effects of SCG-DBS.

Methods: 35 participants with TRD received active or sham stimulation over two 3-month periods. A neuropsychological battery was administered to assess processing speed, learning and memory, and cognitive flexibility. Composite measures were derived for each domain after Period I. A mixed model for repeated measures analysis was performed for each test, with further analysis of significant measures to determine sustainability after Period II.

Results: No significant differences in changes in depression scores were observed between groups. There were no significant deteriorations in cognitive performance following active SCG-DBS. Category Fluency Test performance improved after 3 months of active SCG-DBS (p=0.002); however, this was non-significant after correcting for multiple comparisons and was not observed after Period II (p=0.615).

Conclusions: While no cognitive deterioration was observed following SCG-DBS, significant improvements in cognitive function were not evident. There may be a transient enhancement in processing speed; however, this effect is not fully understood. Future studies should include larger cohorts and extended stimulation periods to explore the long-term effects of SCG-DBS in TRD and the sustainability of improvements in cognitive domains.