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Neurologists Lost Track of Part of the Human Brain And Just Re-Discovered It

The major pathway in the brain wasn’t exactly missing, but science literature appeared to have forgotten about it until now

Early images of the vertical occipital fasciculus, a brain region involved in processing visual information (Jason Yeatman/University of Washington)
smithsonian.com

A disagreement between a teacher and his student may have pushed an important brain tract to the margins of science. Theodor Meynert, a German-Austrian neuro-anatomist had spent years and built his career describing the twists and turns of nerve fiber bundles running through the brain. He was a pioneer in recognizing that mental illnesses are diseases rooted in the biology of the brain. But when his student made a discovery that literally ran counter to his conceptions, he did not publish the finding. 

The student was Carl Wernicke, who would become famous in his own right for discovering a part of the brain important for understanding written and spoken language. Shortly after earning his medical degree, Wernicke was working in Meynert’s lab. There he saw a bundle of fibers in monkey brains that he called the senkrechte occipitalbündel, or "vertical occipital bundle."

The problem was, this bundle ran vertically, and Maynert had already "arrived at the general principle that [nerve bundles] are oriented horizontally, running mostly from front to back within each hemisphere," writes Mo Costandi for the Guardian. Maynert refused to acknowledge the bundle. Or he just wasn’t interested, writes Laura Geggel for Livescience. 

For whatever reason, the nerve tract was only mentioned occasionally in studies over the next century. It fell into such obscurity that a research scientist at the University of Washington’s Institute for Learning and Brain Sciences didn’t recognize the region at all. "It was this massive bundle of fibers, visible in every brain I examined," Jason Yeatman said in a press release, via Loony Labs. He had stumbled upon the bundle while looking at MRI scans of human brains.

"[We] couldn’t find it in any atlas," he told Livescience.com. "We’d thought we had discovered a new pathway that no one else had noticed before." 

But a little more digging revealed the story of Wernicke and the possible disagreement. Yeatman and his colleagues published their rediscovery of the area in Proceedings of the National Academy of Sciences.

Additional scans on 74 volunteers show what this brain region does. It appears to be important in the processing of visual information. The vertical occipital fasciculus or VOF, as it is now known, has been fully measured and described. The Guardian reports:

The new measurements delineate the full extent of the VOF, revealing it as a flat sheet of white matter tracts that extends up through the brain for a distance of 5.5cm, connecting the ‘lower’ and ‘upper’ streams of the visual pathway. These run in parallel, and are sometimes called the ‘What’ and ‘Where’ pathways, for the type of information they carry: the lower stream, connects brain regions involved in processes such as object recognition, including the fusiform gyrus, and the upper stream connects the angular gyrus to other areas involved in attention, motion detection, and visually-guided behavior.

A couple of case studies from the 1970s do mention the region—in both cases women with damage to the VOF could no longer read, though they could understand and write words. The new research also notes that the pathway has unusual myelination—the fatty covering on nerves that insulates and speeds along the passage of electrical signals. Why, the scientists can’t say yet. But at least the nerve tract has at last been found.

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