# Default Mode Network Resting State Connectivity Derived From Task‐Based fMRI: A Validation Study in People With Epilepsy

## TL;DR

This study validates a new method to measure brain connectivity in people with epilepsy using task-based fMRI rest periods instead of separate resting scans.

## Contribution

The intermittent resting state method is validated in a clinical epilepsy cohort for measuring functional connectivity.

## Key findings

- ICA-derived topography of DMN and SMN was similar between standard and intermittent resting state methods.
- Within-network connectivity and hippocampal seed-based analyses showed comparable results across both methods.
- The intermittent resting state method is efficient for studying functional connectivity in epilepsy without additional scans.

## Abstract

Resting state functional connectivity can be measured using resting state functional MRI (fMRI), but also task‐dependent fMRI in blocked designs. The latter has been demonstrated in healthy participants but not yet validated in clinical cohorts. Since functional connectivity of resting state networks (e.g., default mode network [DMN] and somatomotor network [SMN]) is altered in people with epilepsy, and the impact of the disease on the quality of the intermittent resting state data is unclear, we aimed to validate the method using a clinical fMRI in people with epilepsy.

We compared functional connectivity derived from a standard resting state with rest periods of a clinical language fMRI (intermittent resting state) of 92 people with focal epilepsy. Both methods were analyzed across different aspects of functional connectivity: topography, within‐network connectivity, and group‐level comparisons. Therefore, we conducted independent component analyses (ICAs), similarity‐, regions of interest (ROI)‐to‐ROI‐, and second‐level seed‐based analyses.

Results indicated similar ICA‐derived topography of DMN and SMN from both methods. Within‐network connectivity also yielded comparable results. Seed‐based analyses of left and right hippocampal connectivity in people with left and right temporal lobe epilepsy also revealed analogous results, with minor restrictions in right hippocampal connectivity.

The intermittent resting state method produces highly similar results to a standard resting state method in people with epilepsy across different aspects of functional connectivity. It is, therefore, an efficient approach to gain insights into functional connectivity networks in a clinical cohort without performing an additional resting state fMRI.