Hippocampal Functional Connectivity and Cognitive Stability in Parasellar Meningiomas (Studied by the "Virtually Implanted Electrode" Method).

Abstract

Adaptive reactions of the brain ensure cognitive stability of the individual in a fairly wide range of pathological impacts, but the mechanisms for the implementation of such compensatory changes have been poorly studied. The aim of the study was to describe changes in the functional connections of the hippocampus subject to a mild unilateral compression in a sample of patients with parasellar meningiomas.

Materials and methods: A homogeneous sample of 28 patients with parasellar meningiomas adjacent to the hippocampus has been studied. In 16 patients, the tumor was diagnosed on the left side, in 12 patients on the right side. These two groups were comparable in terms of tumor morphometric characteristics and the degree of hemispheric compression. The control group consisted of 31 healthy subjects. All three groups were comparable in age and gender. The "Virtually Implanted Electrode" method was used to describe changes in brain network connectivity. The method allows for the reconstruction of electrical activity in any brain voxel based on its coordinates relative to scalp electrodes. To describe the functional connectivity of the brain, correlation coefficients between all pairs of the selected areas of interest were sequentially calculated.

Results: The comparison of functional connections of the hippocampus in clinical groups and in a group of healthy participants made it possible to identify the following types of dynamics. The first type involves strong and stable hippocampal connections that have not been affected by the pathological process. These are the connections of the hippocampus with the deep stem formations, amygdala, putamen, globus pallidus, and insula. The second type in the clinical groups is characterized by weakening of functional connections of the hippocampus with the structures that transform afferent information flows. Hypothetically, such a weakening could lead to a change in the thresholds of the hippocampal "marking the degree of novelty" of external information flows, being an important way to save individual's resources. The third type is characterized by enhanced functional connections of the hippocampus with the structures supporting executive functions in clinical groups, which is consistent with the facts of increased voluntariness in the implementation of cognitive actions. Compensatory processes of the brain are not symmetrical. The left and right hippocampi differentially alter functional connectivity under adverse conditions. Restructuring of the interhemispheric interaction may also be considered as a factor ensuring cognitive stability.

Conclusion: Changes in the hippocampal functional connections, identified in the clinical groups by the "Virtual Implanted Electrode" method, can be considered as an adaptive brain reaction aimed at maintaining cognitive stability in parasellar meningiomas.