In the realm of weird things that scientists are prone to doing, putting crocodiles in an MRI machine and playing them classical music has to be pretty high up on the list. But that is exactly what a team of scientists recently did, and it could help us understand how animals evolved to process complex sounds.
The researchers wanted to understand how the brain signals of reptiles differed from those of birds and mammals. To find this out they placed them in functional MRI machines to take a peek inside their skulls. This is highly unusual, not only because of the obvious danger of placing Nile crocodiles inside such a machine, but also because it has never been done for cold-blooded animals before.
“In the first step, we had to overcome a number of technical obstacles,” explained Mehdi Behroozi, who co-authored the study now published in the Proceedings of the Royal Society B. “For example, we had to adjust the scanner to the crocodile’s physiology, which differs massively from that of mammals in several aspects.”
The biggest problem to contend with was the temperature. When reading an animal’s brain signal, the machine is looking out for regions of the brain in which the oxygen levels in the blood drop, as this indicates that those parts are active. This process is influenced by the animal’s body temperature, meaning that there is a clear problem if the animal in which you’re scanning is cold-blooded.
The researchers had to experiment to find a room temperature that was not only adequate for the crocodile, but also one that allowed the machine to detect signals. This was further complicated somewhat by the fact that the coils within the scanner also emit heat as they work, and so that also needed to be taken into consideration. The other aspect that also needed to be taken into account was the difference in breathing patterns of the reptiles.
With that all figured out, the researchers could now examine how the crocodiles' brains responded to simple and complex sounds, such as Bach’s Brandenburg Concerto No 4. Having been used in other experiments to test the brains of mammals, the classical tune was a perfect choice for the scaly subjects.
While we know that birds and mammals respond the same way, testing crocodiles would give us an even better understanding of when brains evolved to deal with such complex noises as they sit on a completely separate branch of the evolutionary tree, separated by hundreds of millions of years.
It turns out that their brains respond in a strikingly similar way. This suggests that the ability for creatures to process such complicated noises evolved early on in animals, and can likely be traced back to the same origin in all vertebrates, including those now long extinct.
The work may also pave the way to putting other cold-blooded animals through the similar tests.