Large-scale network mechanisms underlying postoperative cognitive improvement after spine surgery

Background: The outcome of major surgery is determined not only by the success of the procedure itself but also by its neurocognitive effects. We previously reported improved cognition following spine surgery (Müller et al. 2023 Spine), but the mechanisms underlying these changes remain unknown.

Materials and methods: We analyzed resting-state (rs) functional magnetic resonance images of 79 patients (mean/SD age: 71/7 years) acquired at baseline in this previously published trial. For 26 patients, data was additionally available at 3-months follow-up visits. To delineate large-scale connectivity, we calculated functional connectivity (FC) within and between three core neural networks, the central executive network (CEN), the salience network (SAL), and the default mode network (DMN).

Results: FC between CEN and SAL predicted cognitive improvement (beta = 0.36, 95%-CI 0.28 to 0.45, P = 0.033). Average FC between all nodes of the CEN showed changes towards an increase after surgery (beta = 0.057, 95%-CI - 0.01 to 0.123, P = 0.086). Further seed-based FC analyses revealed that this increase was most pronounced in the functional coupling between left dorsolateral prefrontal and right posterior parietal cortex (beta = 0.10, T(24) = 2.73, Punc = 0.012, PFDR = 0.035). The increase of CEN-FC correlated with individual enhancements of executive scores (beta = 0.34, 95%-CI 0.32 to 0.36, P = 0.034).

Conclusion: Integration of activity between the CEN and SAL networks predicted postoperative cognitive improvements, suggesting that less segregated large-scale functional networks may facilitate beneficial cognitive changes following surgery. Postoperative increases in functional coupling may serve as a biomarker for individual improvements in executive functions. These results indicate that surgery should not be routinely deferred in elderly patients due to concerns about postoperative neurocognitive complications. Moreover, our findings highlight potential targets for non-invasive brain stimulation interventions aimed at preventing neurocognitive complications.