Dynamic tractography: Integrating cortico-cortical evoked potentials and diffusion imaging.

Area of Science:

• Neuroscience
• Medical Imaging
• Computational Biology

Background:

• Cortico-cortical evoked potentials (CCEPs) are used to map human brain networks by measuring electrical responses between cortical areas.
• CCEPs alone cannot visualize white matter pathways or predict signal characteristics at downstream sites.
• Diffusion-weighted imaging (DWI) provides information about white matter but lacks direct electrophysiological correlation.

Purpose of the Study:

• To develop and validate a novel "dynamic tractography" approach integrating CCEP and DWI data.
• To investigate the relationship between white matter properties (path length, fractional anisotropy) and CCEP N1 characteristics (latency, voltage, velocity).
• To enhance the understanding of large-scale brain networks supporting cognitive functions.

Main Methods:

• Twenty-three epilepsy patients underwent extraoperative CCEP recordings and preoperative DWI scans.
• CCEPs were elicited using single-pulse electrical stimulation and recorded with subdural grids.
• DWI data and electrode locations were coregistered to quantify white matter pathways and their properties.

Main Results:

• DWI-based path length significantly predicted CCEP N1 latency (R²=0.81) and negatively predicted N1 voltage (R²=0.79).
• Fractional anisotropy (FA) along white matter tracts predicted N1 propagation velocity (R²=0.35).
• Clinical variables did not influence the observed relationships, allowing for pooled group-level analysis.

Conclusions:

• The strength and timing of CCEP N1 responses are significantly dependent on the underlying white matter network's properties.
• Dynamic tractography effectively integrates electrophysiological and imaging data for robust localization of axonal pathways.
• This integrated approach improves the understanding of cortico-cortical connectivity and large-scale brain network function.