Modeling diffusion in white matter in the brain: a composite porous medium

Area of Science:

• Biophysics
• Neuroscience
• Materials Science

Background:

• White matter fascicles are crucial for neural signal transmission.
• Understanding diffusion within these structures is key to diagnosing neurological disorders.
• Current models often simplify the complex microenvironment of white matter.

Purpose of the Study:

• To develop a detailed biophysical model of diffusion within white matter fascicles.
• To investigate the impact of myelin sheath properties on molecular transport.
• To analyze diffusion dynamics in a periodic array of cylindrical tubes representing fascicles.

Main Methods:

• Modeling diffusion as a multi-compartment problem in an array of thick-walled cylindrical tubes.
• Assigning distinct diffusion coefficients and concentrations to inner core, membrane, myelin sheath, and outer medium.
• Simulating molecular transport with an impermeable myelin sheath assumption.

Main Results:

• Demonstrated complete restriction of diffusion within the inner core of the tubes.
• Showcased hindered diffusion in the outer medium due to the tortuosity of the tube array.
• Quantified the influence of varying diffusion coefficients and concentrations across compartments.

Conclusions:

• The model accurately represents diffusion barriers and pathways in white matter fascicles.
• Myelin sheath impermeability significantly impacts molecular diffusion dynamics.
• The findings provide a foundation for more accurate modeling of white matter.