The bundle of nerves that controls the elephant’s trunk contains 400,000 neurons – a lot more than we expected – suggesting the trunk is incredibly sensitive
Elephant trunks may be one of the most sensitive body parts in the animal kingdom.
Michael Brecht at the Bernstein Center for Computational Neuroscience in Berlin and his colleagues dissected the heads of three Asian elephants (Elephas maximus) and five African bush elephants (Loxodonta africana). All the animals had lived in zoos and died of natural causes or had been euthanised because of severe health problems.
These dissections are rare because the procedure is difficult. “The head of an elephant with the trunk and everything is about 600 kilograms,” Brecht says. “Dissecting them requires specialised machinery.”
The researchers wanted to take a closer look at a trigeminal ganglion, a bundle of nerve neurons involved in sensing in an elephant’s trunk and face. Each elephant has two of them. “We found that it weighs about 50 grams,” Brecht says. “The human retina weighs about 0.3 grams – so this is really very big.”
The researchers also counted around 400,000 neurons in the main nerve coming out of the trigeminal ganglion. This was far more than they expected and only slightly less than the number of neurons they found in the elephant’s optic nerve. Optic nerves usually have far more neurons than nerves related to touch because the visual system is typically a lot more complicated.
The team also found that the nerve in the trunk relating to touch was three times as thick as the optic nerve leading to the elephant’s eye. Brecht says this thickness points to how much information can be carried by the neurons and how precise the trunk’s touch system may be.
“Elephants constantly touch things with their trunk,” Brecht says. “They manipulate things with the trunk, they grasp things – a trunk for an elephant is like having a hand.”
He says this study suggests that elephant trunks may be one of the most sensitive body parts anywhere in the animal kingdom.
“But, of course, we can’t say this for certain based on just one experiment,” says Brecht.
“The tactile nature of the elephant trunk has been largely overlooked compared to other tactile systems – such as primate fingertips and rodent whiskers,” says Robyn Grant at Manchester Metropolitan University, UK. “It makes sense that the trunk is really tactile.”
“While we often think about the trunk being moveable and for manipulation, all movement and manipulation is guided by sensation,” says Grant.
Journal reference: Current Biology, DOI: 10.1016/j.cub.2021.12.051
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