Summary: Exposing crocodiles to a variety of auditory and visual stimuli while in an MRI, researchers discover their brain processing patterns resemble that of other mammals and birds. The researchers speculate the fundamental mechanisms of sensory processing were formed at an early evolutionary stage.
What happens in a crocodile’s brain when it hears complex sounds? An international research team headed by Dr Felix Ströckens from the Department of Biopsychology at Ruhr-Universität Bochum (RUB) has provided the answer to this question. In a first, the researchers examined a cold-blooded reptile using functional MRI. They were thus able to determine that complex stimuli triggered activation patterns in the crocodile’s brain that are similar to those in birds and mammals – a deep insight into evolution. The results were published in the journal Proceedings of the Royal Society B: Biological Sciences on April 25, 2018.
Link to dinosaurs
Crocodiles count among the most ancient species of vertebrates and have barely changed over the space of more than 200 million years. Accordingly, they constitute a link between dinosaurs and bird species today. “Analyses of crocodile brains thus provide deep insights into the evolution of the nervous system in mammals and may help us understand at which point certain brain structures and behaviours associated therewith were formed,” explains Felix Ströckens.
Overcoming technical obstacles
The objective pursued by the team of researchers from the Iran, South Africa, France, and Germany was to study Nile crocodiles and to ascertain the way sensory information is processed in their brain. To this end, they deployed functional MRI (fMRI) – a method that is routinely used in clinical diagnostics and research, but which has never yet been utilised to study a cold-blooded reptile. “In the first step, we had to overcome a number of technical obstacles,” says research team member Mehdi Behroozi. “For example, we had to adjust the scanner to the crocodile’s physiology, which differs massively from that of mammals in several aspects.”
Astonishing similarity of patterns
Subsequently, the researchers exposed the animals to various visual and auditory stimuli, including classical music by Johann Sebastian Bach. At the same time, they measured the animals’ brain activity. The results have shown that additional brain areas are activated during exposure to complex stimuli such as classical music – as opposed to exposure to simple sounds. The processing patterns strongly resemble the patterns identified in mammals and birds in similar studies.
Processing patterns formed at an early stage
Consequently, the researchers assume that fundamental neuronal processing mechanisms of sensory stimuli formed at an early evolutionary stage and that they can be traced back to the same origins in all vertebrates.
By successfully deploying fMRI for the examination of a reptile for the first time worldwide, the researchers, moreover, demonstrated that the method does work for poikilothermic organisms. This non-invasive technology can thus be used for many other species that have not yet been studied in depth.
Funding: Funded by the National Research Foundation of South Africa, Thuthuka Grant (TTK14051567366), the German Research Foundation (Gu227/16-1) and the Collaborative Research Centre 874.
Source: Felix Ströckens – RUB
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is in the public domain.
Original Research: Abstract for “Functional MRI in the Nile crocodile: a new avenue for evolutionary neurobiology” by Mehdi Behroozi, Brendon K. Billings, Xavier Helluy, Paul R. Manger, Onur Güntürkün, Felix Ströckens in Proceedings of the Royal Society B. Published April 25 2018.
Functional MRI in the Nile crocodile: a new avenue for evolutionary neurobiology
Crocodilians are important for understanding the evolutionary history of amniote neural systems as they are the nearest extant relatives of modern birds and share a stem amniote ancestor with mammals. Although the crocodilian brain has been investigated anatomically, functional studies are rare. Here, we employed functional magnetic resonance imaging (fMRI), never tested in poikilotherms, to investigate crocodilian telencephalic sensory processing. Juvenile Crocodylus niloticus were placed in a 7 T MRI scanner to record blood oxygenation level-dependent (BOLD) signal changes during the presentation of visual and auditory stimuli. Visual stimulation increased BOLD signals in rostral to mid-caudal portions of the dorso-lateral anterior dorsal ventricular ridge (ADVR). Simple auditory stimuli led to signal increase in the rostromedial and caudocentral ADVR. These activation patterns are in line with previously described projection fields of diencephalic sensory fibres. Furthermore, complex auditory stimuli activated additional regions of the caudomedial ADVR. The recruitment of these additional, presumably higher-order, sensory areas reflects observations made in birds and mammals. Our results indicate that structural and functional aspects of sensory processing have been likely conserved during the evolution of sauropsids. In addition, our study shows that fMRI can be used to investigate neural processing in poikilotherms, providing a new avenue for neurobiological research in these critical species.