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For the first time, scientists have mapped the entire sensory and motor systems of the dolphin brain.
Studying the brains of a deceased common dolphin and pantropical dolphin, researchers found at least two areas linked to hearing — unlike most mammals, which only have one. That makes dolphin brains similar to those of bats — something that is probably related to their use of echolocation to "see" their environments.
"This is surprising because dolphins and bats are far apart on the evolutionary tree," Gregory Berns, lead author of the study and neuroscientist at Emory University, said in a statement. "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."
The study was published on Wednesday in the journal Proceedings of the Royal Society B.
Why did it take so long to get a complete picture of the dolphin brain? Many animals are examined with tracer studies, which involve injecting the animal with a tracer, euthanizing it and sectioning up its brain.
Doing that to a dolphin carries moral complications. With humans and chimps, researchers use something called diffusion tensor imaging (DTI) to map the white matter in their brains. Because dolphins live underwater, putting them in an MRI machine isn't an option, and the brains of recently deceased animals are difficult to find.
The dolphin researchers solved this problem by employing a novel DTI technique that's used to examine post-mortem human brains. This gave them a more complete picture of the white matter pathways in the dolphin brain, which is large compared to most animals, about the size of a football.