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Fascinating fibre images
To gain a better understanding of the brain, researchers need to untangle its vast labyrinth of nerve fibres. Jülich is developing new methods to do just that. A novel imaging technique is now expanding existing approaches.
For her doctoral thesis, Miriam Menzel had intended to further develop an established technique known as polarized light imaging (PLI). This method uses special light, known as polarised light, to visualize the pathways of nerve fibres in brain sections (see infobox). It helps improve our understanding of brain functions as well as diseases such as Alzheimer’s.
Bringing things to light: Polarized light imaging uses light that only oscillates in a single plane. This polarised light is passed through a sample and analysed on the other side. At Jülich, researchers use this method to examine brain sections. The key aspect here is that when the polarized light encounters a nerve fibre as it passes through the sample, its polarization changes in a characteristic way. This change can be measured and used to infer the orientation of the nerve fibres. However, if multiple fibres cross and overlap, the signal becomes ambiguous. Conventional light microscopy cannot visualize fibre orientations in dense fibrous tissue at all.
To analyse PLI and the underlying processes, Menzel simulated them using high-performance computers in close collaboration with the Jülich Supercomputing Centre. In doing so, she discovered unexpected information in the scattered light within the virtually generated images. “Until then, scattered light was regarded as an undesirable by-product in PLI. But the pattern of the scattered light clearly revealed how nerve fibres cross each other,” explains Menzel. This came as a surprise to her, as crossing fibre pathways have posed a major challenge for imaging techniques for many years.
Menzel had an idea: why not use scattered light for a completely new microscopy technique? She illuminated brain sections from many different directions and recorded the scattered light with a camera. From the measured light intensities, she was able to calculate the individual orientations of the nerve fibres – including in areas with densely interwoven fibres. This can be achieved with simple equipment: “We even obtained good measurement results using a rotating torch light and a camera,” she explains. Together with colleagues at the Institute of Neuroscience and Medicine (INM-1), Menzel went on to develop a fully automated method which she named “computational scattered light imaging” (ComSLI). “The method allows the position and orientation of fibre pathways to be reconstructed with high precision,” says the physicist, who now leads a research group as Assistant Professor at TU Delft in the Netherlands, where she continues to develop the technique.
Analysing historical brain sections: To produce ultra-thin, high-quality brain sections, brains are often embedded in wax before being cut. In the process, the regular structure of the nerve fibre sheaths, which is essential for PLI measurements, is destroyed. With ComSLI, however, the directions of fibre pathways can still be determined. This makes the method particularly valuable for large archives containing many thousands of prepared brain sections, such as those held at Jülich. The resulting data can, among other things, complement the BigBrain dataset, a high-resolution three-dimensional reconstruction of the human brain.
At Jülich, the scientists are now combining the established PLI technique with the new ComSLI technique in a targeted way to identify brain regions and fibre pathways affected by neurodegeneration. “Damaged fibre pathways alter the optical properties of brain tissue, which can be visualized using PLI. ComSLI, in turn, allows the course of fibre pathways to be determined independently of disease. By combining the two methods, affected neural connections can be localised with great precision,” says Prof. Markus Axer, head of the “Fibre Architecture” research group at INM-1.
A look into the future: ComSLI can be used not only to analyse brain sections but also other types of biological tissue. Fibrous structures are found throughout the body – for example, muscle fibres and collagen fibres, the latter of which occur, among others, in tendons, cartilage, and bone. The arrangement of collagen fibres can serve as a tumour marker, as its structure is altered by the presence of a tumour. Using ComSLI, it may even be possible to visualize fibre architectures during an operation – without having to cut the tissue. Miriam Menzel and her team in Delft are currently working on this.
This text is taken from the 1/26 issue of effzett. Text: Janosch Deeg, Pictures Infobox: Forschungszentrum Jülich / Sascha Kreklau
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Last Modified: 18.08.2026