The bundle of nerves that controls the elephant’s trunk contains 400,000 neurons – far more than we expected – suggesting the trunk is incredibly sensitive
January 20, 2022
The trunk of elephants is perhaps 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 of the animals had lived in zoos and either died of natural causes or were euthanized due to serious health issues.
These dissections are rare because the procedure is difficult. “An elephant’s head with trunk and everything weighs about 600 kilograms,” Brecht explains. “Dissecting them requires specialized 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. “We found that it weighed around 50 grams,” says Brecht. “The human retina weighs about 0.3 grams – so it’s really, really 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. The optic nerves generally have many more neurons than the nerves related to touch, because the visual system is generally much more complicated.
The team also found that the trunk nerve related to touch was three times thicker than the optic nerve leading to the elephant’s eye. Brecht says that this thickness indicates the amount of information that can be carried by neurons and the accuracy of the trunk’s tactile system.
“Elephants constantly touch objects with their trunks,” Brecht explains. “They handle things with the trunk, they grab things – a trunk for an elephant is like having a hand.”
He says this study suggests elephants’ trunks may be one of the most sensitive body parts in the animal kingdom.
“But, of course, we can’t say that for sure based on a single experience,” Brecht says.
“The tactile nature of the elephant trunk has been largely overlooked compared to other tactile systems – such as the fingertips of primates and the whiskers of rodents,” says Robyn Grant at Manchester Metropolitan University, UK. “It makes sense that the trunk is really tactile.”
“While we often think of the trunk as mobile and intended 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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