In a nutshell:

The first high-resolution 3D map of white matter in marmosets brings us a step closer to understanding brain connectivity in humans.

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Most of the human brain is made up of white matter – the tissue underneath the surface that contains brain cells and their long protruding nerve fibres. Like a public transport network covering a big city, the white matter contains many intersecting pathways that connect cells in different parts of the brain. This connectivity allows us to handle complex learning, memory and cognitive tasks.

Despite the importance of white matter to brain activity in primates, researchers didn’t have a clear picture of its overall structure or individual pathways. A better understanding of its connectivity could help to explain symptoms in human diseases such as depression and schizophrenia.

Thanks to research from the Brain Function CoE and the US National Institutes of Health, we now have the first complete high-resolution 3D map of white matter in marmosets. The research team included Brain Function CoE investigators Marcello Rosa from Monash University and Piotr Majkafrom the Nencki Institute in Poland, and partner investigator David Leopold from the National Institute of Mental Health (NIMH) in the USA.

The NIMH researchers developed a method to scan marmoset brains at much higher resolution than ever before. These small primates were used because their brain is organized in a similar way to that of larger primates like humans. Their brains are also small enough to fit into the most powerful high-resolution scanners.

The researchers combined imaging data with information from the Brain Function CoE’s Marmoset Brain Connectivity Atlas, which maps the connections between different areas of the cortex – the part of the brain that covers the white matter.

The resulting map of white matter organization reveals a structure that is even more complex than previously suspected. The unprecedented resolution of the map also uncovered features that hadn’t been seen before and allowed the researchers to correctly identify features that had been misidentified in previous maps.

This map opens the way to a precise understanding of the changes in brain connectivity that are related to diseases. When similar data are obtained for other primates, the marmoset white matter map will also be a useful resource for comparing the structures and evolution of primate brains.

To encourage use of this resource, the researchers have made the map and its associated data freely available online through the Marmoset Brain Mapping Project.

Next steps:
The researchers are continuing their work on the Marmoset Brain Mapping Project by examining how brains differ within the marmoset population. They have scanned the brains of many more marmosets, and are combining this imaging data with the the brain connectivity and white matter maps to analyse how brain and head size and shape – and brain connectivity – vary between individuals within a population.

Liu, C., Ye, F. Q., Newman, J. D., Szczupak, D., Tian, X., Yen, C. C., Majka, P., Glen, D., Rosa, M. G. P., Leopold, D. A., & Silva, A. C. (2020). A resource for detailed 3D mapping of white matter pathways in the marmoset brain. Nature Neuroscience. doi: 10.1038/s41593-019-0575-0

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