# Voxel-based morphometry and functional connectivity changes are associated with cognitive function in herpes simplex virus encephalitis

## TL;DR

This study shows that brain structure and connectivity changes in herpes encephalitis patients are linked to cognitive decline and inflammation.

## Contribution

The study identifies specific brain regions and inflammatory markers associated with cognitive impairment in herpes simplex encephalitis patients.

## Key findings

- HSE patients had reduced grey matter volume in the hippocampal gyrus, precuneus, and posterior cingulate gyrus.
- Cognitive scores were positively correlated with grey matter volume and functional connectivity metrics in HSE patients.
- Elevated IL-6 levels were negatively associated with brain metrics and cognitive outcomes.

## Abstract

Herpes simplex encephalitis (HSE) is a severe neurological condition associated with significant cognitive impairment and structural brain changes. This study aimed to investigate microstructural and functional connectivity (FC) alterations in HSE patients and their association with cognitive function, cerebrospinal fluid (CSF) parameters, and inflammatory markers.

A single-center cohort study was conducted with 73 HSE patients and 76 cognitively unimpaired controls. Voxel-based morphometry (VBM) and resting-state functional MRI (rs-fMRI) were used to assess VBM grey matter volume (GMV) and FC. Cognitive function was evaluated using the Montreal Cognitive Assessment (MoCA). CSF pressure, protein levels, and proinflammatory cytokines (IL-6, IL-1β, IL-2, IL-4, IL-5, IL-10) were measured. Statistical analyses included group comparisons and multivariable regression adjusted for age, gender, and hypertension.

HSE patients exhibited significant GMV reductions in the right hippocampal gyrus, left precuneus, and left posterior cingulate gyrus (all p < 0.001). Enhanced FC was observed between the left hippocampus and medial prefrontal cortex (mPFC), while weakened connectivity was noted between the left precuneus, posterior cingulate gyrus, and mPFC in controls. Cognitive scores (MoCA) were lower in HSE patients (p < 0.001) and positively correlated with GMV and FC metrics (p < 0.05). Elevated CSF pressure, protein, and proinflammatory cytokines (particularly IL-6) were negatively associated with cerebral metrics (p < 0.001). A significant interaction between IL-6 and cerebral metrics further influenced cognitive outcomes (p < 0.05).

HSE is associated with distinct microstructural and functional connectivity changes that are correlated with cognitive impairment and neuroinflammation. Our findings suggest a potential interaction between IL-6 levels, cerebral alterations, and cognitive dysfunction, which may inform the exploration of neuroimaging and inflammatory biomarkers in personalized therapeutic strategies. However, these represent observational associations, and further prospective studies are needed to validate these findings and establish causal relationships.