Squeeze it like toothpaste: The flexible brain of marsupial mammals

January 27, 2021

Being stretchy and squeezable may be the key to finding space for the brain in mammals, including humans.

An international study, co-led by Flinders University's Vera Weisbecker, has revealed that marsupial mammals like possums, kangaroos, and wombats appear to have a lot of flexibility when it comes to accommodating their brains into their skulls.

"The brain is one of the heaviest parts of the head, particularly in smaller mammals. But it needs to be placed in a way that doesn't interfere with the many vital functions of the head, such as seeing, hearing, smelling and of course feeding," says Dr. Weisbecker.

"Stowing" a large brain into the head is a general challenge for mammals, which have much larger brains relative to their body size compared to their reptile-like ancestors. It is also a particularly intriguing issue in humans and their primate relatives, which tend to have extremely large relative brain sizes compared to other mammals."

"We wanted to use a diverse group of mammals to assess if there is general pattern of brain shape variation to explain the ability of mammals to fit their brains into the great diversity of head shapes without interfering with head function. Marsupial mammals fit the bill perfectly because they are a well-understood group of mammals with diverse head sizes and functions."

The team used CT scanning and 3D visualisation to extract the shape of the brain cavity in the diverse group of Australian marsupial mammals with the results published in the International Journal Of Organic Evolution.

"These so-called "endocasts" give us a good idea of what the brain itself looks like", says Dr. Weisbecker.

"I then placed landmarks - which work a bit like a coordinate system for shape - all over the endocasts of just under 60 marsupial species, including some really cool fossils like the marsupial lion."

When co-author Dr. Emma Sherratt from The University of Adelaide analysed the data, the team were in for a surprise:

"The biggest difference between the brains is basically whether they are more cylindrical or more globular. We were struck by how extreme this stretch-compress pattern was - we saw brains that look like marbles, and others that nearly look like tubes!" says Dr. Sherratt.

"Intriguingly, this matches the characteristically rounded shape of the human brain, which is sometimes thought to arise from the need to "stack" all the brain tissue into the skull efficiently," says Dr. Weisbecker.

"It is therefore possible that human brain shape arises from an ancient general tendency of the brain to assume a range of shapes from rounded to elongate."

Another interesting find was the many unusual brain shapes the team saw.

"Within the general pattern of spherical versus stretched-out, we saw some outlandish endocast shapes. For example, some species had totally flat brains, while others seemed to have parts of the brain "squished aside" by the bone around the middle ear."

The researchers say that the Tasmanian tiger has enormous olfactory bulbs, which are responsible for smell, and some unusually compact and rounded cerebral hemispheres.

"We believe that a round-to-cylindrical brain shapes are probably the most easily achieved evolutionary pathway of fitting the brain into the skull. However, within this overall pattern, the brain seems incredibly flexible, nearly as if it was toothpaste than can be squeezed into any mould," says Dr. Weisbecker.

"This might also explain why we saw substantially different brain shapes in individuals of the same species."

The teams find matches well with evidence that the brain of some mammals can change size and shape during an animals' lifetime.

"We suspect that a flexible brain is the key to success in other animals as well. For example, some crocodiles and ancient coelacanth fishes have extremely long brains; and birds have their eyes imprinted on their brain shape. It appears that the brain is capable of functioning regardless of where it goes in the skull."

The research shows brain function might not be easy to determine from brain shape.

"We found no correspondence of brain shape with movement patterns, for example if animals a species climbs trees, glides, hops, or walks on all fours."

"We suspect that the overall shape of the mammalian brain is strongly determined by the requirements of the skull. Understanding specific adaptations of the brain probably require investigation of finer detail than overall brain shape."
-end-


Flinders University

Related Brain Articles from Brightsurf:

Glioblastoma nanomedicine crosses into brain in mice, eradicates recurring brain cancer
A new synthetic protein nanoparticle capable of slipping past the nearly impermeable blood-brain barrier in mice could deliver cancer-killing drugs directly to malignant brain tumors, new research from the University of Michigan shows.

Children with asymptomatic brain bleeds as newborns show normal brain development at age 2
A study by UNC researchers finds that neurodevelopmental scores and gray matter volumes at age two years did not differ between children who had MRI-confirmed asymptomatic subdural hemorrhages when they were neonates, compared to children with no history of subdural hemorrhage.

New model of human brain 'conversations' could inform research on brain disease, cognition
A team of Indiana University neuroscientists has built a new model of human brain networks that sheds light on how the brain functions.

Human brain size gene triggers bigger brain in monkeys
Dresden and Japanese researchers show that a human-specific gene causes a larger neocortex in the common marmoset, a non-human primate.

Unique insight into development of the human brain: Model of the early embryonic brain
Stem cell researchers from the University of Copenhagen have designed a model of an early embryonic brain.

An optical brain-to-brain interface supports information exchange for locomotion control
Chinese researchers established an optical BtBI that supports rapid information transmission for precise locomotion control, thus providing a proof-of-principle demonstration of fast BtBI for real-time behavioral control.

Transplanting human nerve cells into a mouse brain reveals how they wire into brain circuits
A team of researchers led by Pierre Vanderhaeghen and Vincent Bonin (VIB-KU Leuven, Université libre de Bruxelles and NERF) showed how human nerve cells can develop at their own pace, and form highly precise connections with the surrounding mouse brain cells.

Brain scans reveal how the human brain compensates when one hemisphere is removed
Researchers studying six adults who had one of their brain hemispheres removed during childhood to reduce epileptic seizures found that the remaining half of the brain formed unusually strong connections between different functional brain networks, which potentially help the body to function as if the brain were intact.

Alcohol byproduct contributes to brain chemistry changes in specific brain regions
Study of mouse models provides clear implications for new targets to treat alcohol use disorder and fetal alcohol syndrome.

Scientists predict the areas of the brain to stimulate transitions between different brain states
Using a computer model of the brain, Gustavo Deco, director of the Center for Brain and Cognition, and Josephine Cruzat, a member of his team, together with a group of international collaborators, have developed an innovative method published in Proceedings of the National Academy of Sciences on Sept.

Read More: Brain News and Brain Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.