The elephant in the room

I open my Neuroscience Research Methods course at DePaul University by showing a picture of this sculpture, a depiction of a classic Indian parable.

Surrounding an elephant are several blind men, each of them reaching to feel this new animal they know nothing about. One of them feels the tail and says “Hm, this animal must be like a long frayed rope.” The second touches the tusk and deduces “Oh, this is a dangerous animal, covered in sharp spears.” The third, feeling the trunk says “Wait, this animal must be a very large snake!”

The researchers who published this 2022 study in the journal Current Biology called “Trigeminal ganglion and sensory nerves suggest tactile specialization of elephants” are most likely the ones who felt the trunk. 

The story they tell is fascinating, especially to neuroscientists.

The elephant trunk is well known to be a complex organ. Probably their main way of interacting with their surroundings, the trunk is flexible, strong, and versatile. Watching elephant babies trying to control their trunk will make you baby crazy. And with more than 40,000 muscles in their trunk, it’s no surprise that it’s wildly uncoordinated for a good part of their early lives. 

For all of those muscles to move the way they are supposed to, each one needs to receive motor neuron innervation. These descending, downward projections are a part of the animal’s peripheral nervous system, specifically, the efferent branch of their somatic nervous system.

But what about the other process, the afferent, upwards going signals that transmits feeling information from the trunk to the brain? These neurons and connections are the focus of the study. 

The research group was in a very fortunate position to ask some interesting questions about the elephants, examining the nerve bundles that pass information towards the brain. The most interesting picture shows the massive diameter of one branch of their trigeminal nerve and how it completely dwarfs the spinal cord. 

In other words, there is more nerve volume to transmit sensory information from the trunk than the whole massive body!