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Evolutionary biologists report that they have combined PET scans of modern pigeons with studies of dinosaur fossils to answer a perennial question in biology: How did birds’ brains evolve to allow them to fly? can be enabled.
Answer There appears to be an adaptive increase in the size of the cerebellum in some fossil vertebrates. The cerebellum is a region at the back of the bird’s brain that is responsible for movement and motor control.
The research findings have been published in the journal Proceedings of the Royal Society B.
“We found that circuits in the cerebellum were more active than in any other part of the brain when birds transitioned from rest to flight,” said the study’s co-author. Paul Gignacan associate professor at the University of Arizona College of Medicine – Tucson, the study of neuroanatomy and evolution. He is also a research associate at the American Museum of Natural History.
“We then looked at skulls matching this region in dinosaur and bird fossils to determine when the cerebellum grew,” Gignac said. “The first pulse of extension occurred before dinosaurs took wing, suggesting that avian flight uses an ancient and well-conserved neural relay, but with a unique level of activity.”
Scientists have long thought that the cerebellum should be important in bird flight, but they did not have direct evidence. To demonstrate its value, the new study combined modern PET scan imaging data from common pigeons with the fossil record, examining the brain regions of birds in flight and the brain regions of ancient dinosaurs. A PET scan shows how organs and tissues are working.
“Powered flight among amphibians is a rare event in evolutionary history,” said lead author Amy Balanov of the Johns Hopkins University School of Medicine.
In fact, only three groups of vertebrates evolved to fly: the extinct pterosaurs — the terror of the skies during the Mesozoic Era, which ended 65 million years ago — bats and birds, Balanov said. The three flight groups are not closely related on the evolutionary tree, and the key factors enabling flight in all three are still unclear.
In addition to the apparent physical adaptations for flight, such as long upper limbs, specific types of wings, a streamlined body and other features, the team researched to find features that created a flight-ready brain.
To do this, the team enlisted biomedical engineers from New York’s Stony Brook University to compare the brain activity of modern pigeons before and after flight.
The researchers performed PET scans to compare activity in 26 brain regions while the bird was resting and immediately after flying from one perch to another for 10 minutes. They scanned eight birds on different days. A PET scan uses a compound similar to glucose to detect which is most absorbed by brain cells, indicating increased energy use and thus activity. The tracer is excreted from the body within a day or two.
One of the 26 regions – the cerebellum – showed a statistically significant increase in activity levels between resting and flying in all eight birds. Overall, the level of increased activity in the cerebellum was significantly different compared to other brain regions.
The researchers also detected increased brain activity in the so-called optic flow pathways, a network of brain cells that connect the retina in the eye to the cerebellum. These pathways move across the visual field.
Balanov said the team’s findings of increased activity in the cerebral and optic flow pathways were not necessarily surprising, since these regions are hypothesized to play a role in flight.
What was new in their research was linking findings from the cerebellum of flight-capable brains in modern birds to the fossil record, which showed that bird-like dinosaur brains had the brain conditions for powered flight. How did you start preparing?
To do this, the team used a digitized database of endocasts, or molds of the interior of dinosaur skulls, which resemble brains when filled.
They then identified and traced a massive increase in cerebellum volume in some of the earliest species of maniraptoran dinosaurs, which preceded the first appearance of powerful flight among primitive bird relatives, including Archeopteryxa winged dinosaur.
The researchers, led by Balanov, also found evidence in endocasts of increased tissue folding in the cerebellum of early miniraptorans, indicating increased brain complexity.
The researchers caution that these are preliminary findings, and changes in brain activity during powered flight may also occur during other behaviors, such as gliding. They also note that their tests involved straight flight, with no obstacles and a smooth flight path, and that other brain regions may be more active during complex flight maneuvers.
The research team plans ahead to identify the precise regions of the cerebellum that enable the flight-ready brain and neural connections between these structures.
Co-author Gabriel Beaver of the Johns Hopkins University School of Medicine said scientific theories for why the brain gets bigger include the need to cross new and different landscapes in evolutionary history, setting the stage for flight and other locomotor styles. Setting up
Other authors of the study include Elizabeth Ferrer of the American Museum of Natural History and Samuel Merritt of the University. Lemez Saleh and Paul Waska of Stony Brook University. Eugenia Gould of the American Museum of Natural History and Suffolk University; Jesuss MargOnn-lobeof the Autonomous University of Madrid; Mark Norrell of the American Museum of Natural History; David Ouellette of Weill Cornell Medical College; Michael Salerno of the University of Pennsylvania; Akinobu Watanabe of the American Museum of Natural History, the New York Institute of Technology College of Osteopathic Medicine and the Natural History Museum of London; and Shui Wei of the New York Proton Center.
This research was funded by the National Science Foundation.
Source: University of Arizona
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