Longitudinal surface-based spatial Bayesian GLM reveals complex trajectories of motor neurodegeneration in ALS

TL;DR

This study introduces a novel longitudinal surface-based Bayesian GLM to analyze fMRI data in ALS, revealing complex activation trajectories related to disease progression and highlighting the importance of individualized analysis.

Contribution

The paper presents a new longitudinal extension of the surface-based spatial Bayesian GLM, enabling precise detection of brain activation changes in ALS patients over time.

Findings

Identified an inverted U-shaped activation trajectory in ALS progression.

Faster disease progressors show more extreme hyper- and hypo-activation.

Surface-based Bayesian modeling enhances understanding of neurodegenerative dynamics.

Abstract

Longitudinal fMRI datasets hold great promise for the study of neurodegenerative diseases, but realizing their potential depends on extracting accurate fMRI-based brain measures in individuals over time. This is especially true for rare, heterogeneous and/or rapidly progressing diseases, which often involve small samples whose functional features may vary dramatically across subjects and over time, making traditional group-difference analyses of limited utility. One such disease is ALS, which results in extreme motor function loss and eventual death. Here, we analyze a rich longitudinal dataset containing 190 motor task fMRI scans from 16 ALS patients and 22 age-matched HCs. We propose a novel longitudinal extension to our cortical surface-based spatial Bayesian GLM, which has high power and precision to detect activations in individuals. Using a series of longitudinal mixed-effects models to subsequently study the relationship between activation and disease progression, we observe an inverted U-shaped trajectory: at relatively mild disability we observe enlarging activations, while at higher disability we observe severely diminished activation, reflecting progression toward complete motor function loss. We observe distinct trajectories depending on clinical progression rate, with faster progressors exhibiting more extreme hyper-activation and subsequent hypo-activation. These differential trajectories suggest that initial hyper-activation is likely attributable to loss of inhibitory neurons. By contrast, earlier studies employing more limited sampling designs and using traditional group-difference analysis approaches were only able to observe the initial hyper-activation, which was assumed to be due to a compensatory process. This study provides a first example of how surface-based spatial Bayesian modeling furthers scientific understanding of neurodegenerative disease.