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ABSTRACT
Objective
To examine the roles of the default mode network (DMN) and executive control network (ECN) in prolonged recovery after mild traumatic brain injury (mTBI), and relationships with indices of white matter microstructural injury.
Methods
Seventeen mTBI patients with persistent symptoms were imaged an average of 21.5 months post-injury, along with 23 healthy controls. Resting-state functional magnetic resonance imaging (rs-fMRI) was used to evaluate functional connectivity (FC) of the DMN and ECN. Diffusion tensor imaging (DTI) quantified fractional anisotropy, along with mean, axial and radial diffusivity of white matter tracts.
Results
Compared to controls, patients with mTBI had increased functional connectivity of the DMN and ECN to brain regions implicated in salience and frontoparietal networks, and increased white matter diffusivity within the cerebrum and brainstem. Among the patients, FC was correlated with better neurocognitive test scores, while diffusivity was correlated with more severe self-reported symptoms. The FC and diffusivity values within abnormal brain regions were not significantly correlated.
Conclusion
For female mTBI patients with prolonged symptoms, hyper-connectivity may represent a compensatory response that helps to mitigate the effects of mTBI on cognition. These effects are unrelated to indices of microstructural injury, which are correlated with symptom severity, suggesting that rs-fMRI and DTI may capture distinct aspects of pathophysiology.
Biographical note
Mr. Jimmy Wong was a graduate student in the Institute of Biomedical Engineering (BME) at the University of Toronto under the supervision of Dr. Tom Schweizer.
Dr. Nathan Churchill is a researcher in the Keenan Research Centre for Biomedical Science at St. Michael’s Hospital. His research focus is on functional imaging of the brain, and the use of statistical techniques to optimize the correction of noise and artifacts, with an emphasis on functional Magnetic Resonance Imaging (fMRI).
Dr. Simon Graham is a medical physicist and biomedical engineer with diverse interests in the development of MRI technology for clinical applications involving the brain. Dr. Graham is a Professor in the Department of Medical Biophysics at the University of Toronto.
Dr. Andrew Baker is the Chief of the Department of Critical Care and the Medical Director of the Trauma and Neurosurgery Program at St. Michael’s Hospital. Dr. Baker is the inaugural Cara Phelan Chair of Critical Care Medicine and a Professor in the Departments of Anesthesia and Surgery at the University of Toronto.
Dr. Tom Schweizer is a cognitive neuroscientist with diverse interests in neuroimaging and neuropsychology. Dr. Schweizer is an Associate Professor in the Faculty of Medicine (Neurosurgery) at University of Toronto and the interim director of the Keenan Research Centre for Biomedical Science.
Supplemental data
Supplemental data for this article can be accessed online at https://doi.org/10.1080/02699052.2022.2163290
List of Abbreviations
AD Axial Diffusivity
AFNI Analysis of Functional Neuroimages
BOLD Blood Oxygen Level-Dependent
BSRs Bootstrap Ratios
BW Bandwidth
DKI Diffusion Kurtosis Imaging
DLPFC Dorsolateral Prefrontal Cortices
DMN Default Mode Network
DSS Digit Symbol Substitution Test
DST Digit Span Test
DTI Diffusion Tensor Imaging
DTI-TK Diffusion Tensor Imaging ToolKit
DVARS Temporal Derivative’s Root-mean-square Variance over Voxels
ECN Executive Control Network
EPI Echo Planar Imaging
FA Fractional Anisotropy
FC Functional Connectivity
FD Framewise Displacement
FDR False Discovery Rate
fMRI Functional Magnetic Resonance Imaging
FOV Field of View
FSL FMRIB Software Library
FWHM Full Width at Half Maximum
GCS Glasgow Coma Scale
GSC Graded Symptom Scale
ICBM International Consortium for Brain Mapping
IIT Illinois Institute of Technology
MD Mean Diffusivity
MFG Middle Frontal Gyrus
MNI Montreal Neurological Institute
MPFC Medial Prefrontal Cortex
MPRAGE Magnetization-Prepared Rapid Gradient Echo
mTBI Mild Traumatic Brain Injury
NODDI Neurite Orientation Dispersion and Density Imaging
PC Principal Component
PCA Principal Component Analysis
PCC Posterior Cingulate Cortex
RD Radial Diffusivity
RMS Root-mean-square
RMSD Root-mean-square Displacement
rs-fMRI Resting-state Functional Magnetic Resonance Imaging
SAC Standardized Assessment of Concussion
SLF Superior Longitudinal Fasciculus
SMA Supplementary Motor Area
SMG Supramarginal Gyrus
SN Salience Network
TE Echo Time
TI Inversion Time
TMT Trail Making Test
TR Repetition Time
VFT Verbal Fluency Test
Disclosure statement
No potential conflict of interest was reported by the authors.