Biomedical Imaging and Instrumentation
Thalamic Structural Connectivity Alterations in Patients with Epilepsy
Sarah E. Gatti
Undergraduate Student
Vanderbilt University
Bossier City, United States
Lucas Sainburg
PhD Student
Department of Biomedical Engineering, Vanderbilt University, United States
Victoria Morgan
Principle Investigator
Vanderbilt University Institute of Imaging Science, Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, United States
Behnaz Akbarian
PhD Student
Department of Biomedical Engineering, Vanderbilt University, United States
Liliana Martinez
Undergraduate Researcher
Department of Biomedical Engineering, University of Louisville, United States
Andrew Janson
Post Doctorate
Department of Biomedical Engineering, Vanderbilt University, United States
Dario Englot
Principle Investigator
Department of Neurological Surgery, Vanderbilt University Medical Center, United States
Sub-Track: Magnetic Resonance Imaging and Applications (MRI)
There are multiple complications paired with the presence of epilepsy, including a higher risk for self-harm1, memory impairments2, learning disorders3, and sudden unexpected death4. Epileptic seizures involve widespread network interactions between cortical and subcortical structures where there has been a disruption of the normal balance of excitation and inhibition5,6. Temporal lobe epilepsy (TLE) is a form of focal epilepsy in which seizures are generated within the temporal lobe. Electrical stimulation of the thalamus, a deep brain region, can reduce seizure frequency in TLE due to the connectivity between the thalamus and other brain regions7. The white matter tracts providing connections from the thalamus can be estimated noninvasively using diffusion-weighted MRI (DWI), which quantifies the diffusivity of water in the brain. DWI can be used to obtain measures of structural connectivity, the strength of these connections between brain regions8. Previous studies have shown how large-scale brain networks are altered in TLE9,10, however, here we aim to investigate the effects of TLE on structural brain networks of thalamic sub regions. We hypothesized that thalamic structural connectivity, measured with DWI, is altered in TLE compared to healthy controls.
This study included 30 right TLE patients and 105 healthy controls. Subjects underwent a T1-weighted scan (1x1x1 mm3) and diffusion-weighted imaging (2.5x2.5x2.5 mm3, 92 directions, b = 1600 s/mm2) on a 3T MRI scanner. 115 cortical and subcortical regions of interest and 12 thalamic subregions (6 on each side) were segmented from the T1-weighted scan.
Spherical deconvolution was used to estimate fiber orientation distributions from the DWI data11. The thalamus was then seeded for probabilistic tractography with a minimum streamline length of 20 mm and 2500 streamlines per voxel in controls and patients (Fig 1). Structural connectivity was computed as the number of streamlines between two regions weighted by streamline length and the inverse of region size. Structural connectivity was obtained between each thalamic subregion and all other brain regions to obtain a 12 x 127 structural connectome for each participant.
A two-sample t-test was used to compare the structural connectivity between patients and controls at each connection in the connectome. MATLAB 2021a and MRtrix were used for processing and statistics.
Our results show that 347 connections out of 1524 were different between patients and controls (puncorrected < 0.05; Fig 2). More than 56% of these were connections from the right thalamus. This is expected given these patients’ epileptic foci are on the right side.
All thalamic subregions had some connections that were different between patients and controls, however, the anterior nuclei had the most, with over 50% of the connections different between patients and controls. These altered connections from the anterior nucleus were also primarily increases in structural connectivity in patients. Both the right and left anterior thalamus nuclei were also affected given that more than 25% of the connections from these regions had a significant change, which mostly increase in structural connectivity. This aligns with previous research that shows medial and anterior nuclei are impacted by TLE12,13 The lateral dorsal posterior and pulvinar regions had a generally lower connectivity in patients than in controls while anterior, medial, and central median lateral regions had a generally higher connectivity in patients than in controls (Fig 2). The ventral regions had more varied connectivity differences between patients and controls (Fig 2).
Here we found that the structural networks of the thalamus are altered in TLE. These findings may contribute to a better understanding of the role of the thalamus in TLE, potentially leading to improved treatment for those with epilepsy.