Nerve fibers in the brain of a rat (left) and a pigeon (left), imaged with 3D polarized light imaging. Copyright: Axer et al., Forschungszentrum Jülich
Innovative microscopy reveals unexpected similarities between mammals and birds.
Some birds can achieve exceptional cognitive performance – but their brains were thought to be quite disorganized compared to mammals. Scientists from Bochum (RUB), Düsseldorf (HHU), Jülich (FZJ) and Aachen (RWTH) show for the first time remarkable similarities between the neocortex of mammals and sensory brain regions of birds: Both are wired in horizontal layers and vertical columns. The finding refutes 150-year-old assumptions. A method developed by brain researchers from Jülich and Düsseldorf provided decisive findings. The results were recently published in the journal science.
Birds and mammals have the largest brains for their size. Otherwise, they have little in common, so the assumption of scientists for more than a hundred years: Mammalian brains have a cerebral cortex that consists of six horizontal layers and columns that run perpendicular to these layers. In contrast, the bird’s brain appears to be poorly organized at first glance and only shows clusters of cells with more or less density.
“Given the amazing cognitive performance that birds can achieve, however, it was assumed that their brains are better organized than previously thought,” says Prof. Dr. Onur Güntürkün, head of the biopsychology work unit at the Faculty of Psychology at RUB and an expert in bird recognition.
In fact, researchers led by Dr. Christina Herold (C. and O. Vogt Institute for Brain Research, HHU) and Dr. Martin Stacho (RUB) has now succeeded in proving that the brains of birds and mammals look surprisingly similar in their organization.
The fibers in the avian brain run horizontally and vertically, just like in the mammalian neocortex.
The fiber structure of pigeons and different mammals in comparison. The 3D PLI method shows the directions of the nerve fibers color-coded. The representations shown here do not reflect the true size – a human brain is about 500 times larger than a pigeon’s brain. Copyright: HHU Düsseldorf / Herold et al.
So far it has not been possible to map the fiber structure of larger areas of the bird’s brain with the necessary information accuracy. Commonly used techniques are either limited to small tissue samples or lack the resolution and sensitivity to uncover the microstructural features that define the neural organization of the brain. The level in between therefore remained in the dark.
“3D-PLI has a slightly lower resolution than tracing methods, but can analyze large volumes of tissue in a reasonable amount of time – a decisive advantage,” explains Dr. Markus Axer, head of the fiber architecture group at Forschungszentrum Jülich. Using this method, the researchers were able to analyze three complete pigeon brains with a resolution of 1.3 micrometers (millionths of a millimeter). 250 sections per brain were scanned with high resolution and reconstructed in 3D.
“3D-PLI is a technology that contributes significantly to a deeper understanding of the connectivity of the brain and makes it possible to identify similarities and differences in neural networks between species”, emphasizes Prof. Katrin Amunts, director of the two institutes in Jülich and Düsseldorf.
Since the method is computationally intensive, the researchers use the FENIX supercomputer platform to process the data. FENIX is a European network of high-performance computing centers, to which the Jülich Supercomputing Center also belongs. It is part of the new EBRAINS infrastructure developed by the Human Brain Project. EBRAINS offers neuroscientists around the world a number of advanced new methods and resources, including the 3D atlases of the human brain, BigBrain and Julich-Brain, which were created in Jülich and Düsseldorf.
Further tracing experiments in Bochum made it possible to examine the networking of cells in the bird’s brain in detail. The technique uses tiny crystals that spread into the smallest branches of nerve cells in brain slices. “In a similar way, it was shown that the structure consists of columns in which signals are transmitted from top to bottom and vice versa, and long fibers that run horizontally,” explains Onur Güntürkün. However, this structure is only found in the sensory areas of the bird’s brain. Other areas, such as B. Associative areas are organized differently.
Reference: “A cortex-like canonical circuit in the forebrain of the bird” by Martin Stacho, Christina Herold, Noemi Rook, Hermann Wagner, Markus Axer, Katrin Amunts and Onur Güntürkün, September 20, 2020, science.
DOI: 10.1126 / science.abc5534
