Structural coarse-graining enables noise-robust functional connectivity and reveals hidden inter-subject variability

TL;DR

This paper presents a novel framework combining structural coarse-graining and spectral noise filtering to improve the reliability of functional connectivity estimates from limited fMRI data, revealing hidden inter-subject variability.

Contribution

The authors introduce a new method that reduces network dimensionality and filters noise, enabling more accurate functional connectivity analysis with fewer time points.

Findings

Improved detection of inter-subject variability in functional networks.

Standard pipelines are heavily influenced by non-stationary fluctuations.

The proposed method reveals broader variability patterns obscured by traditional approaches.

Abstract

Functional connectivity estimates are highly sensitive to analysis choices and can be dominated by noise when the number of sampled time points is small relative to network dimensionality. This issue is particularly acute in fMRI, where scan resolution is limited. Because scan duration is constrained by practical factors (e.g., motion and fatigue), many datasets remain statistically underpowered for high-dimensional correlation estimation. We introduce a framework that combines diffusion-based structural coarse-graining with spectral noise filtering to recover statistically reliable functional networks from temporally limited data. The method reduces network dimensionality by grouping regions according to diffusion-defined communication. This produces coarse-grained networks with dimensions compatible with available time points, enabling random matrix filtering of noise-dominated modes. We benchmark three common FC pipelines against our approach. We find that raw-signal correlations are strongly influenced by non-stationary fluctuations that can reduce apparent inter-subject variability under limited sampling conditions. In contrast, our pipeline reveals a broader, multimodal landscape of inter-subject variability. These large-scale organization patterns are largely obscured by standard pipelines. Together, these results provide a practical route to reliable functional networks under realistic sampling constraints. This strategy helps separate noise-driven artifacts from reproducible patterns of human brain variability.