Most scientific research is, by its nature, rather boring. Research projects that reshape the way we think about fundamental topics are rare by definition, which means most progress happens piecewise, built up by a series of papers and articles, which then spawn more papers and articles, which collectively lead to advances in the field. Every now and then, however, you hear about projects that sound rather interesting — including one experiment in which scientists drugged crocodiles and shoved them into MRI machines to find out how they’d respond to classical music.
This is rather less ridiculous than it might seem at first glance. The team in question was investigating the evolution of complex stimulus processing. Crocodiles have remained phenotypically similar for tens of millions of years; crocodilians like Deinosuchus that lived 80-73 million years ago look quite similar (if much larger) than crocodiles today. The last common ancestor between crocodiles and birds lived 240 million years ago, which makes modern crocodiles an interesting comparison case for both mammals and birds. And one of the interesting things about mammals and birds is that we handle complex audio processing in areas of our brains that are functionally similar, even if the regions themselves are quite physiologically distinct. The question was, would reptiles show similar functional similarity, or did they evolve an entirely different method of processing this information? The only way to find the problem was to chuck a crocodile in an MRI and make sweet lo play it some music.
This is easier said than done. “The difficulty in scanning crocodiles—beside being a little bit dangerous for the experimenter—is that they are cold-blooded reptiles,”” lead researcher Dr. Felix Ströckens, from the Department of Biopsychology at Ruhr University Bochum, told Gizmodo. “We thus had to find a temperature which allowed us to pick up a good signal and was comfortable for the animal. We also had to keep this temperature stable within the scanner which is relatively difficult since the coils used for scanning also emit heat.”
The crocodiles were tested with a wide range of stimuli, including various colors, simple sounds, and complex audio, with the latter provided by Johan Sebastian Bach’s Brandenburg Concerto No. 4. The team found that there are areas of the crocodilian brain that respond to complex audio stimuli that don’t light up in the same fashion when visual stimuli or simple audio stimuli were provided, but that did respond to more complex audio signals. This subdivision of capability, in which certain brain regions are activated in response to complex audio that are not activated by simple tones, appears to echo the design of the mammalian and bird brain, despite hundreds of millions of years of evolution between the three groups.
This finding suggests that hierarchical signal processing is a strongly conserved trait in evolutionary history. A conserved trait is a trait that has remained more or less unchanged since it first evolved, suggesting that it offers a strong evolutionary advantage. The team hasn’t proved the hypothesis yet, as more data is needed on higher-order visual processing in reptiles. But the team’s findings suggest that this basic method of processing information was already present in the brains of the last common ancestor between birds, reptiles, and mammals — a creature that likely lived more than 300 million years ago.