How Dolphins 'hear' a sound

Unlike most mammals that primarily process sound in a single area, two areas of the dolphin brain are associated with the auditory system, a new research says.

"Dolphins are incredibly intelligent, social animals and yet very little is known about how their brains function, so they have remained relatively mysterious," said lead author of the study Gregory Berns, neuroscientist at Emory University in the US.

For the study, the researcher mapped for the first time the sensory and motor systems in the brains of dolphins.

"We now have the first picture of the entire dolphin brain and all of the white matter connections inside of it," Berns said.

The researchers applied a novel technique of diffusion tensor imaging (DTI) on the preserved brains of two dolphins who died after being stranded on a beach in North Carolina more than a decade ago.

The method for using DTI on a non-living brain was developed relatively recently and had previously only been used for research on deceased humans, primates and rats.

The study focused on the dolphin auditory system, since dolphins - along with several other animals, such as bats - use echolocation to sense their environments.

"We found that there are probably multiple areas in the dolphin brain associated with auditory information, and the neural pathways look similar to those of a bat," Berns said.

"This is surprising because dolphins and bats are far apart on the evolutionary tree. They diverged tens of millions of years ago but their brains may have evolved similar mechanisms for using sound not just to hear, but to also create mental images," Berns added.

"For decades, we've thought of the dolphin brain as having one primary auditory region," said study co-author Lori Marino, a neuroscientist specialising in the brains of dolphins, whales and other cetaceans.

"This research shows that the dolphin brain is even more complex than we realized," Marino said.

The study was published in the journal Proceedings of the Royal Society B.