Colour play: the 3D-PLI image shows the course of the nerve fibres, here in the human hippocampus, where memory is located.
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Research
So much for “birdbrain”!
Research
So much for “birdbrain”!
Skilled craftsmen: straight-billed crows build tools which they use to fish for tasty tidbits in rotten tree trunks.
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The bird brain was previously considered unstructured. A method developed at Jülich has now proven otherwise, which could explain the smart behaviour of some types of birds. According to the journal Science, the finding is one of the ten most important breakthroughs of 2020.
It beats its European relatives by a beak: the straight-billed crow of the Pacific island of New Caledonia. This crow builds tools from branches and twigs to reach its favourite food – larvae and maggots in rotten wood. Even more amazing: it makes the tool not only to get at the food, but also to fish for even better tool-building materials. Science sees the use of tools that do not directly serve to obtain food as a typical characteristic of intelligence. No wonder, then, that behavioural scientists consider the straight-billed crow to be one of the most intelligent birds. However, fellow species are also considered cunning and astute: corvids, for example, deceive their competitors by hiding and stealing food; grey parrots have a talent for mimicking human speech; and magpies recognise their own reflection – all amazingly intelligent feats.
Picture above: Skilled craftsmen: straight-billed crows build tools which they use to fish for tasty tidbits in rotten tree trunks.
But how do our feathered friends succeed in thinking in such a complex way? After all, their brain is no larger than a walnut at most, and researchers have previously searched in vain for a structured cerebral cortex like that of mammals. A part of the cerebral cortex referred to as the neocortex is, in a sense, the control centre of human intelligence. This unique structure is responsible for our ability to dream, speak or think in complex ways.
An answer has now been found by a team led by Prof. Katrin Amunts and Prof. Markus Axer from the Institute of Neuroscience and Medicine (INM- 1) in collaboration with researchers from the universities of Düsseldorf, Aachen and Bochum: they were the first to discover structures in the bird brain that resemble the cerebral cortex of mammals. As in the neocortex, the birds’ nerve cells form horizontal layers and vertical columns. The team published their findings in the journal Science – and these findings ended up as one of the magazine’s top ten most important findings in 2020.
Markus Axer uses the 3D-PLI method to make nerve networks in the brain visible. Making brain structure visible
The Jülich researchers used a special type of light microscopy to make larger areas of the bird brain visible (see infobox): “We brought together the techniques of polarized light microscopy with the efficient data analysis of supercomputing. The result is the so-called ‘3D Polarized Light Imaging,’ or 3D-PLI for short,” explains Axer, who heads a research group on the method at Forschungszentrum Jülich. The images taken with 3D-PLI show how brain regions are connected via nerve fibres, making their position, course and orientation visible – that is, the paths along which signals are transmitted. Axer sums their research up: “Our results suggest that bird and primate brains, despite all their obvious differences, show strong similarities when observed in high-resolution detail – which also suggests similar thinking abilities.”
“Our results suggest that bird and primate brains show strong similarities when observed in high-resolution detail.”
Markus Axer
Grey parrots have a strong gift for speaking and help their fellow parrots without immediate reciprocation. Axer has been working on polarized light microscopy imaging in Jülich since 2006. The physicist established the 3D-PLI method at Forschungszentrum Jülich and continually advanced it. He had previously adopted it from his older brother Hubertus, who is a specialist in neurology and anatomy. “The method has become somewhat of a family affair,” says Axer. Back then, however, his big brother had lacked the means to improve the technology.
The researchers have now already used the method to analyse three complete pigeon brains at a resolution of 1.3 thousandths of a millimetre. In each case, 250 wafer-thin sections were scanned at high resolution and reconstructed three-dimensionally. In the near future, these will be the basis of the first bird brain atlases, which Axer and his team want to make available to the community via the Human Brain Project’s EBRAINS brain research. Prof. Katrin Amunts, director of the participating institutes in Jülich and Düsseldorf, also shares their enthusiasm: “3D-PLI contributes significantly to a deeper understanding of the brain’s connectivity structure. The method also makes it possible to detect similarities and differences in the structure of neuronal networks across species.”
Axer assumes that the method will shine the “right polarization light” onto other brain regions. One thing is certain: “For the bird brain, it has definitely been a breakthrough.”
Katja Lüers
Magpies recognise themselves in the mirror. What is 3D-PLI?
The famous German neuroanatomist and brain mapper Korbinian Brodmann (1868–1918) already observed that light refracts differently in brain tissue than in other body tissue. Science speaks of birefringence. This is caused by the myelin sheath, which covers many nerve fibres like an insulation. Researchers measure this birefringence using a special light microscopy technique: polarized light microscopy. A microscope of this kind has special filters that only allow certain light to pass through, called polarized light.
“We measure how this polarized light changes when we shine it through brain tissue. With the help of supercomputers and efficient data analysis, we calculate the paths of the nerve fibres,” explains Axer. With this “3D Polarized Light Imaging” method, 3D-PLI for short, the researchers are able to visualise the orientation, position and course of nerve fibres for the entire brain.
Course of nerve fibres; as well, in the human hippocampus in another sectional plane.
Course of nerve fibres in the cerebellum of a guenon (primate)
Nerve fibres in the brain of a rat
Nerve fibres in the brain of a pigeon; for comparison, a human brain is about 500 times larger than a pigeon brain.
The method fills a gap that other methods overlook: they either provide a very detailed view of the brain using tissue samples that show individual cells and their connections, which is time-consuming, or, as with MRI images, they make whole brain regions visible quickly, but in low resolution.
“3D-PLI is a go-between,” says the deputy director of INM-1. That is precisely its advantage and thus, Axer is convinced: “We can look at the whole brain – not at every single cell, but in more detail than in an MRI, and we can do so in a reasonable amount of time. That’s a good compromise!” It is a compromise that makes findings possible which are as groundbreaking as in the case of the bird brain.
How 3D-PLI makes paths visible
PHOTOS: Forschungszentrum Jülich/Markus Axer, Katrin Amunts, Forschungszentrum Jülich/Ralf-Uwe Limbach, John Gerrard Keulemans, DRAWaDREAM/shutterstock.com, Piotr Krzeslak/shutterstock.com, VIDEO: Forschungszentrum Jülich