Hemodynamic variability in soldiers with trauma: Implications for functional MRI connectivity studies.

Area of Science:

• Neuroimaging
• Cognitive Neuroscience
• Psychiatry

Background:

• Functional MRI (fMRI) measures neural activity indirectly via the hemodynamic response function (HRF).
• HRF exhibits significant spatial and inter-subject variability, potentially compromising fMRI study reliability.
• Previous research links neurochemical alterations in PTSD to HRF shape modifications.

Purpose of the Study:

• To investigate the impact of mental disorders, specifically PTSD and mTBI, on HRF variability.
• To assess the influence of HRF variability on functional connectivity (FC) findings in clinical populations.
• To introduce voxel-level HRF estimation and its implications for rs-fMRI analysis.

Main Methods:

• Whole-brain resting-state fMRI (rs-fMRI) data from soldiers with PTSD/mTBI (N=87) and combat controls.
• Hemodynamic deconvolution to estimate voxel-wise HRF and identify regional HRF aberrations.
• Seed-based FC analysis using regions-of-interest (ROIs) with differing HRFs between groups.

Main Results:

• Significant HRF aberrations were identified in subcortical and default-mode regions in PTSD and mTBI groups.
• A portion of group differences in FC analysis (without deconvolution) was attributable to HRF variability.
• This study provides the first evidence of voxel-level HRF alterations in PTSD and mTBI and their impact on FC.

Conclusions:

• HRF variability significantly impacts rs-fMRI findings, particularly in psychiatric populations like PTSD and mTBI.
• Conventional rs-fMRI analyses may yield unreliable results due to unaddressed HRF variability.
• Incorporating hemodynamic deconvolution into preprocessing is recommended to enhance the reliability of rs-fMRI connectivity studies.